I'm a title. Click here to edit me.
10 Reasons Why a Mini-Split Ductless Flare May Leak Refrigerant!
On a mini-split ductless system, two copper tubes are needed to transport the refrigerant. These copper tubes are referred to as the line set and they connect the indoor head unit to the outdoor heat pump or condensing unit. Two flare connections are needed at the indoor head unit and two flare connections are needed at the outdoor mini-split unit. Things to consider: · A standard system has four flare connections while a multi-zone system has more flare connections for the additional indoor head units. · The pressure of the refrigerant in the system will be anywhere from approximately 100-400 PSI depending on whether the unit is in heating or air conditioning mode. Therefore, it is essential to have all the flare connections correctly sealed so that refrigerant does not leak out of the system. Listed below are the ten most common reasons mini-split flares may leak. Problem #1: The Flare Size is too Small · At the end of the copper tube, the surface on the flare face must be big enough to take up the full amount of space inside the flare nut. The reason for this is so that the tube's flare face entirely covers over the seat of the flare adapter. This will give you the best chance at sealing this connection point. · If the tube flare is not very wide, it will only cover half of the connection point and will barely seal the joint. · The flare may accidentally be made too small if the flare block is not tight enough. If the block is not tight enough, the copper tube will slide while you are trying to make the flare. Use the rod that comes with the flare block to tighten the block as hand tightening may not be sufficient. Problem #2: Over-Tightening the Flare Connection · This could be caused by using adjustable wrenches that are too large. If the wrenches are too large, you will not feel when the joint is tight and you will easily over-tighten the joint. · Over-tightening can cause the threads of the flare nut and adapter to become stripped/dethreaded. · This causes the flare face inside the nut to be crushed or cracked. · Over-tightening may cause the tubing inside the flare nut to spin, which scratches the flare seat or flare face so that it no longer has a good seal. · Always use a torque wrench when connecting mini-split lines. The mini-split manufacturer’s installation literature should list the correct amount of foot-pounds that the connections need to be tightened to. Each manufacturer's required foot-pounds may be different. Eight Head Mini-Split Torque Wrench: Problem #3: The Cone is Scarring up the Flares · This may be due to the fact that refrigerant oil was not added to the cone of the tool before flaring the copper. · It could be because the cone itself is bad or rough. · An eccentric flaring tool would likely be the best tool to avoid scarring the flare face. This is because the cone of this tool has the least amount of surface contact while forming the flare out of any tool. Eccentric flaring tool: Problem #4: No Refrigerant Oil on the Flare Face · A small amount of refrigerant oil or Nylog Blue (which is compatible with all refrigerants) should be applied to the flare face before tightening the connection. · Make sure that oil or Nylog does not get onto the threads of the flare as this will act like a lubricant. This may cause you to accidentally over-tighten the flare or to strip the threads on the nut or the flare adapter. · You don’t want to get the Nylog Blue inside the tubing as it may clog strainers if it is pushed into the system by the refrigerant. · Carry a small container of POE oil, PVE oil, mineral oil, or other comparable oils with you if you choose not to use Nylog. Small Nylog Blue: Problem #5: An Incorrect Flare Nut is Being Used · When working on a mini-split system, be sure to only use flares nuts that have been specifically manufactured for mini-split ductless units. · A flare nut could crack over time if it is not designed to handle the pressure of R-410A or other refrigerants. · A flare nut could crack if it is not designed to be exposed to the outdoor environment. Problem #6: A Scratch on the Flare Face or Flare Adapter · If there is a scratch on either the flare face or the flare seat of the adapter, it may be enough to allow refrigerant to leak out of the system. Problem #7: Preparation of the Copper Tubing · If the copper tubing is squished while it is being cut, it usually cannot be used no matter how much you deburr the inside of the tube or re-round the outside of the tube. · Using a stick reamer or a unibit to ream the hole in the end of the copper tubing may not be a good idea. It could result in the inside of the tube being scarred, which you don’t want to happen. This could cause your flare face to be scarred before you even make the flare! · Deburr the hole at the end of the copper tubing well before starting to flare. Problem #8: Using an Improper Flaring Tool · The correct flaring angle to use for HVAC and plumbing is one with a 45 degree flare. There are flaring tools out there that have different angles such as 37 degrees, which you don't want for flaring refrigerant tubing. · A standard flaring tool, a process flaring tool, or an eccentric flaring tool will create the correct 45 degree angle needed for a refrigerant tube flare. · A spin flare will create a smaller angle flare but while the copper tube is still hot, it can be tightened to the flare adapter which will stretch the flare face to 45 degrees. Spin Flares: Here is a video I made using spin flaring and spin swaging bits: Problem #9: Improperly Torqued Flares · Read the manufacturer’s literature to learn the recommended foot-pound torque. Some manufacturers data will only be in metric. Make sure to have a torque wrench with heads that include standard and metric. Eight head torque wrench: · Remember that the torque value may vary from manufacturer to manufacturer and it will vary depending on the size of the copper tube, flare adapter, and flare nut size. · An adjustable head torque wrench can be used when working on systems with many flare nut sizes. This allows you to speedily adjust your torque wrench. Adjustable head torque wrench: Problem #10: The Pressure Test · If you pressure test the system at a low PSI, a leak may not show up until you run the system in heating mode. · When using a compound manifold gauge set, you may have to let the pressure test sit on there longer because the incremental changes in a compound gauge are very small. · A leak shows up quicker when using a digital manifold gauge compared to a compound manifold gauge set because the digital display indicates changes in tenths of a PSI. · You want to pressure test the system below the max design pressure of the unit. Follow the manufacturer’s installation literature for pressure testing so that you do not over-pressurize a system. · If a leak is detected, use a non-corrosive bubble leak detector on the exposed joints in order to find the leak or use an ultrasonic leak detector. Bubble leak detector spray bottle: 8-ounce bubble leak detector with dabber: Ultrasonic leak detector: · Do a pressure test before doing the vacuum procedure, otherwise if there is a leak, you will pull in the humid air surrounding the outside of the leak spot into the tubing. · When performing a vacuum, pull the vacuum down below 500 microns and perform a standing vacuum test. Try to target at least 200-300 microns while the vacuum pump is running, before performing the standing vacuum test. Here is a video on vacuuming a mini-split ductless unit and breaking the vacuum with refrigerant from the bottle: Here is a video showing the 10 reasons why mini-split flares may leak: Check out our Quizzes to test your knowledge here! Follow us on Facebook for Quick Tips and Updates here! Published: 5/20/2020 Author: Craig Migliaccio About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at & &
20 Causes of Low Indoor Airflow on Ducted HVAC Units!
In this HVAC training article, I discuss 20 AIRFLOW Problems that you may find on ducted gas furnaces, air conditioners, heat pumps, air handlers, and packaged units. Some problems happen over time due to lack of maintenance while others may have occurred during the initial installation. Low air flow is a big deal, so it is important to figure out what is causing this issue. For a furnace it could overheat. For an air conditioning system, the evaporator coil could freeze. If the problem isn’t that bad, you can still have longer run times, lower capacity and lower electrical efficiency. The system's lifespan can also be reduced. Let's be aware of what these problems are in order to fix them. Below, I discuss each of the 20 problems. Problem #1 Dirty Indoor Air Filter It is important to change out the air filters, so that they don’t get clogged with dust. Keep in mind, while most systems have one air filter, some systems may have multiple filters. You need to look at the interior walls and the ceiling in each room of the building to see if there are multiple FRAG's (filter return air grilles) and change the filters in each one. Remember, you could find more than one filter in a row in the main return duct. This usually happens on accident when the occupant doesn't know the location of the original filter and adds another because they think that the system is not currently equipped with one. Take your time, investigate, look for filter racks cut into the duct, in the return near the furnace/air handler, inside the unit, and at the grilles. After you initially investigate, you will know for future service. Problem #2 Air Handling Cabinet – Loose Insulation This area may be overlooked. Inspect the inside of the air handler, furnace, or packaged unit cabinet. The glue that holds the insulation in place may come undone. This happens more often then you may think. Be aware because when the blower motor shuts off, the insulation may fall back into it's normal spot but while the system runs, the insulation sticks to the side of the blower motor squirrel cage and restricts the airflow. Problem #3 Dirty Blower Wheel When doing a preventative maintenance, clean off the blower wheel fins inside the blower squirrel cage. Make sure that they are as smooth as possible. You can use a brush and shop vac to clean them off. The blower wheel becomes less effective at moving air as dust accumulates on the blower wheel. Problem #4 Dip Switches Never Set Properly If the airflow dip switches or pin connector on the main control board were never set properly, this will cause an incorrect airflow speed. The system's control board determines what speed the ECM blower motor should run at. Set the airflow speed based on the unit's BTU/HR heat removal or heat gain capacity. For air conditioning, refer to the outdoor unit rating plate for the BTU/HR size. Problem #5 Find The Supply Registers You will need to find all of the supply registers. This may require you to move around furniture etc. to ensure that they are all exposed and fully open. Problem #6 Return Grill and Supply Registers: Too Small and/or Not Enough Be sure to consider the size and number of the return grilles and supply registers for the system size. This is an initial design mistake that we find when servicing existing units. Problem #7 Filter Is Too Restrictive If the air filter is too restrictive, you can go with a less restrictive type. The filter manufacturer should have the pressure drop noted on either the packaging or in the service literature. The higher the pressure drop, the more restrictive to the airflow. There are different types of filters available with varying pressure drops. A pleated filter that is 3” or 4” wide may be a good choice if there is room for a wide filter rack to be installed. Wide filters are often used to lower the pressure drop while still filtering the air because more surface area equals less restriction. Problem #8 Secondary Heat Exchanger Clogged With Dust When noticing low airflow, the issue could be the secondary heat exchanger on a 90% efficient furnace. This is the first coil downstream of the blower motor that could get clogged with dust and block the airflow. Problem #9 Airflow Going Unchecked It is important to measure the airflow going across the coil. You can do this by using the Temp Rise formula, a Hot Wire Anemometer, or by measuring the total external static pressure and comparing it to the manufacturer's guidelines. Check out these videos related to this process using the Temp Rise Formula, External Static Pressure and Hot Wire Anemometer. Problem #10 Supply Flex Not Installed Properly On The Collar Look at the supply flexes to see how they are installed. Issues with incorrect installation will cause it to fall off over time, especially if it gets kicked in the attic or there are no hangers holding it in place in the crawl space. The flex could also fall off due to it's weight over time or as a result of the air pressure in the duct. The supply air could be flowing right into the crawl space. Make sure flexes are installed properly and tightly onto the collar with zip ties, screws and/or tape. Problem #11 Clogged Evaporator Coil The evaporator coil could be clogged with dust. This happens as a result of not having a filter installed on the system. This is often an overlooked airflow blockage because it is not easily seen. A significant static pressure drop across the indoor evaporator coil signals a clogged coil. Problem #12 Frozen Evaporator Coil This can happen due to 1 of the 3 following issues: (1) Low refrigerant charge (2) Liquid line restriction (3) Low indoor air flow With a frozen coil, the air cannot pass through to the supply ducts. We have an additional article which covers “Troubleshooting an Air Conditioning System with a Frozen Evaporator” . This article differentiates between a low refrigerant charge, low airflow and a liquid line restriction. Problem #13 Acoustical Liner Blocking Air Flow A duct that has internal acoustical liner may have some of the liner pulled off of the interior wall, partially blocking the duct. Liner is glued and buttoned in place. If the glue or buttons let go, the liner can get sucked back into return and block the airflow. The acoustical liner may have been used as duct insulation instead of installing insulation on the outside of the duct. The real use of an acoustical liner is to quiet the noise in a short return duct. Make sure that the interior of the duct is clear of obstructions. Problem #14 Leaky Joints In Duct Work Check to make sure that all joints are sealed up well. We don’t recommend using tape directly on the metal because the metal has oil on it so the tape will not seal properly. Seal the joints with Duct Sealant (Mastic). This can be purchased in a caulk tube or tub. We have links below: Duct Mastic in the Caulk Tube: Duct Mastic Tube: Problem #15 Improper Size for Supply / Return Trunk Ducts The internal duct size and static pressure may not be sufficient to allow the correct amount of airflow needed across the indoor evaporator coil. In order to find the BTU/HR size of the outdoor unit, look at the rating plate of the outdoor unit. The BTU size is usually incorporated into the model number. Design or improve the existing duct work to accommodate the BTU size by using Manual D for residential systems. Problem #16 Squished Duct Look over the ductwork to locate improperly installed and squished ducts. Some ducts may not be squished but have too many turns or be too long. In this case, airflow will not make it to the supply register at full capacity. Problem #17 Too Many 90 Degree Turns In the Main Trunk Duct Keep turns to a minimum when designing ducts. Remember every time you add a 90 degree turn, it isn’t just the length of the turn that is added to the total length of the duct. The turn is adding a significant equivalent length of duct to the system. Problem #18 Supply Trunk Duct Is Reduced Too Far too Soon I often find that the main trunk duct is reduced too small in size before the last supply runs are added to the main trunk. This results in low airflow to each of the supply registers that these flexes or round ducts are connected to. Problem #19 An Animal Has Made A Nest with the Return or Supply Air Flex A collapsed flex may be found in an unsealed crawl space, such as under a mobile home. If the return flex has been ripped open by an animal, the flex will collapse in on itself when the system turns on. It is very important to make sure that the crawl space is sealed up. Problem #20 Duct Touching the Concrete Floor or Ground A duct making direct contact with a concrete floor or the ground in a crawlspace will eventually rot out and leak. I have seen this quite a bit where a downflow furnace has the supply duct under the home and the supply duct lowers down too far and is in direct contact with the wet ground. Other times, the concrete is continually wet and the duct rusts. The duct eventually rots out and the building owner calls the service tech out on a low airflow call. I hope this review was helpful with solving your airflow issues. Check out our video on this topic. If you want to learn about refrigerants and how they work in a system, check out our “Refrigerant Charging and Service Procedures for Air Conditioning” book . Test your knowledge with our 1,000 question workbook along with the answer key! We also have quick reference cards for use out in the field! Bundle Packs are a great way to save and get faster shipping! Check out Check out our free Quizzes to test your knowledge here! Check out our Free Calculators here! Tools that we use: Follow us on Facebook for Quick Tips and Updates here! Published: 04/14/2021 Author: Craig Migliaccio About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 16 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at & &
40 Vacuum Tips for HVACR Technicians! Avoid Frustration!
I put this list together to make sure that HVACR technicians don’t have to undergo the same frustrations, loss of time, and expenses that I did when trying to figure out solutions to vacuum problems! I am happy to say that I no longer have issues with my vacuums and if there is a problem, I can usually figure out the solution quickly without frustration! Below are my top 40 tips for techs when pulling a vacuum! Hoses 1. Hoses may be rated for vacuum or just for positive pressure. Those rated only for positive pressure may not work well compared to vacuum rated hoses. Positive pressure rated hoses may leak some of the vacuum! 2. Replace your hose end gaskets because they break down and are torn over time! Gaskets are inexpensive and it doesn’t take a long time to replace them! These are obvious, potential leak spots if not taken care of! Also, adding a drop of refrigerant oil or Nylog on the gasket can help seal the gasket to the port of the unit. Gaskets: Nylog: 3. Remember, the less hoses included in your vacuum setup, the less chances for vacuum leaks! 4. To attain a fast vacuum, use short, large diameter, vacuum rated hoses! 5. Vacuum hoses do not need to be expensive ones. I usually use two hoses total, one 3/8” hose for the vapor line port and one ¼” hose for the liquid line port. The 3/8” hose has a 3/8” hose end on one side and a ¼” hose end on the other side. The hose I use for the liquid line is 1’ long with ¼” connectors on the ends. 3/8” vacuum hose with a 1/4" connector and a 3/8" connector: ¼” vacuum hose 1’ long: Sometimes on the liquid line, I use a 3/8" hose with 1/4" connectors on both ends: 6. Don’t trust hoses to hold the vacuum when performing a ten-minute standing vacuum test! Hoses and/or hose ends may leak! Depending on the setup used, you can avoid including the hoses during the "standing vacuum test". The standing vacuum test is also known as the decay test. It is when the vacuum pump is off and isolated while the vacuum gauge still reads the vacuum level in the system. To learn more about the step by step procedures, check out our Book! Our full outline and sample pages are here! 7. Don’t trust valves on hoses to be rated for deep vacuum. Often times, these valves will leak and the vacuum level will be lost. Only trust the vacuum rated valve on the valve core removal tools. 8. Set aside certain hoses specifically for doing vacuums only and not recovery or normal service. This way, you will always know that your vacuum hoses are in good condition.
9. If you use valve core removal tools in your vacuum setup, you will never get refrigerant oil into your dedicated vacuum hoses. This will keep your hoses in good condition for the next vacuum because you won’t have old oil that has absorbed moisture from the air, in your hoses. Example: After I break the vacuum with refrigerant, I re-install the valve core and remove the valve core removal tool from the port. Then I attach my normal service hoses for checking the charge. Because of this, my vacuum hoses are only used for vacuums and no refrigerant oil enters them. Video: 10. When using valve core removal tools, a valve core depressor is not needed on the end of the vacuum hoses. Make sure to remove the valve core depressor at the end of the vacuum hose because it will act like a restriction for your vacuum. Valve Cores and Valve Core Removal Tools 11. Some people refer to these as “Schrader valves” instead of “valve cores” and vice versa. Some may never even hear them referred to as the other name so keep this in mind when you are communicating with techs! 25 pk of replacement valve cores: 12. If valve cores are left in the ports during the vacuum process, they will act like restrictions and prolong the time it takes to attain a deep vacuum. 13. If valve cores are removed with valve core removal tools prior to performing the vacuum, don’t try to put the valve cores back in until after there is positive refrigerant pressure inside the tubing, otherwise you will lose part of your vacuum! 1/4" valve core removal tool: 14. If valve core removal tools are connected at the system ports during a vacuum setup, mount the vacuum gauge to the side of the valve core removal tool to get the most accurate vacuum level reading. 15. When vacuuming from two ports, attach the vacuum gauge to the valve core removal tool mounted to the larger of the two line-set tubes, the vapor tube. This will give you a more accurate vacuum than on the smaller liquid line. If the vacuum gauge were attached to the valve core removal tool on the liquid line, the vacuum level may read lower than what the rest of the system is currently at. 16. When vacuuming from two ports, include a 3rd valve core removal tool in the setup. This one will be mounted to the side of the valve core removal tool on the vapor line and the vacuum gauge can be mounted to this third tool. This third tool is used exclusively to valve off the vacuum gauge prior to adding positive refrigerant pressure in the lines. Remember that if the service valves are opened to break a vacuum, both refrigerant and oil will travel up into the vacuum gauge sensor. This oil may contaminate the sensor. (Also, make sure to remove the valve core from the side of the valve core removal tool, which is mounted to the large vapor line. This is where the third tool is mounted so you don’t want this section closed off by the valve core.) 17. After vacuuming, don’t remove the vacuum gauge prior to adding refrigerant into the system’s tubing to break the vacuum, otherwise air could enter the tubing during the removal. If a third valve core removal tool is used, simply turn the valve to the off position to protect the vacuum gauge. 18. When reinstalling your valve cores, make sure that the front of your valve core removal tool is not squishing the inner rubber gasket, or it will partially close off the section that the valve core needs to be inserted through. 19. After re-installing the valve cores, leak checking can be done very easily by using a cap with a small hole drilled in the end and bubble leak detector applied to the cap end. Using the cap with a hole in the end will not allow any bubble leak detector to enter the port and valve core area. If there is leak at the valve core, the technician will see a bubble being blown very quickly. Add the correct cap to the port when leak testing is complete. Small bottle of bubble leak detector: Spray bottle of bubble leak detector: Related video: 20. On a Mini-split, where only one port is available, two valve core removal tools can be mounted at this one port location. One valve core removal tool is used to remove the valve core from the port and the other tool can be used to valve off the vacuum gauge prior to breaking the vacuum inside the tubing with refrigerant. One vacuum hose can be used to connect from the tool to the vacuum pump 1/4" valve core removal tool: 5/16" valve core removal tool: Video: Manifolds 21. Some techs include their manifold gauge set in the vacuum setup. They may work well for a while but over time, they tend to leak. I had several gauge sets leak the vacuum and they caused me frustration and time trying to figure out what the problem was! The manifold gauge set may work fine for positive pressure but they may not work well for vacuums! 22. Adding a manifold to your vacuum setup will increase the amount of hoses needed to pull a vacuum. The more hoses, the more chances for leaks in your setup. 23. On a two port system, you can vacuum from both ports using a two hose setup without attaching the manifold gauge set. The removal of the manifold gauge set from the vacuum setup will reduce the potential for leaks and speed up the vacuum process because there are less restrictions, turns, and hoses. Related video: Vacuum Pumps 24. Use a vacuum pump that has two or three ports to attach the vacuum hoses to instead of using a manifold as a tee. 25. Not all vacuum pumps are created equal. Some cheap version may not be able to pull a deep vacuum. 26. If the vacuum pump oil is not changed regularly, the vacuum pump may not be capable of pulling a deep vacuum. Don’t wait until the vacuum oil changes color. Replace the oil after use, especially after vacuuming an older existing system! Moisture from the system gets trapped in the oil and it doesn’t allow the vacuum pump to perform optimally. 27. Not all vacuum pumps come with a gas ballast. A gas ballast on a vacuum pump can help to reduce the amount of water that gets entrained in the vacuum pump oil. The gas ballast can be open prior to starting the vacuum pump until roughly the 15,000 micron level. After this, close the ballast and let the pump continue to lower the vacuum level. 28. Never mount a vacuum gauge near the vacuum pump because the vacuum gauge will show a much lower vacuum level than is currently within the system’s tubing. Vacuum Gauge 29. Not all vacuum gauges are created equal and not all expensive vacuum gauges work well. Make sure to do your research before buying and check with other techs to see which brand/type seems to work well. Below is the one that I use in my company which is the same model that my students used in the shop at the HVACR school. Vacuum Gauge: 30. Keep the vacuum gauge as close to the unit as possible so that you can read the true vacuum level inside the system, not just the vacuum level in the hose near the vacuum pump. 31. During the vacuum, if the indoor blower motor is running, heat is introduced at the indoor evaporator coil. This reduces the possibility of water freezing in the tubing during the vacuum procedure. This is only needed when vacuuming a system with a high water content in the tubing. Questions and Problems 32. Make sure to perform a pressure test prior to performing a vacuum. If there is a leak when you are trying to vacuum, you will pull the humid air from outside the tubing into the tubing. 33. The EPA 608 required vacuum level is currently 500 microns but most of us shoot for 200-300 microns for our finished vacuum level. 34. After reaching the required vacuum level, perform a 10-minute long standing vacuum test with the vacuum pump isolated from the system to verify that no water, air, nitrogen, or leaks exist in the system. After the 10 minute standing vacuum test, break the vacuum with refrigerant from the bottle or from the system. 35. A triple evacuation does not need to be performed if during the standing vacuum test of a single evacuation, the vacuum level does not rise. For instance, if you vacuum down to 200 microns and the vacuum level does not rise during the standing vacuum test with the vacuum pump off, the system is verified as having no air, nitrogen, water, or leaks. The triple evacuation is only needed if the technician is having a hard time removing the moisture from the empty system. Video of a single and triple evac on a minisplit: 36. If the unit you are vacuuming is used/old and the pressure test holds but the vacuum seems to leak, the leak spot may be at the top of the service valve where the stem O-ring seals up against the brass. This O-ring may be dry or was overheated during a brazing process. If the system is empty, try adding Nylog or refrigerant oil at the top of the valve on the inside and move the inner stem up and down to wet the O-ring! This may seal up the leak. Nylog: Video: 37. If you are vacuuming from both ports on a used system and the vacuum level is jumping around, there may be a problem with one or more oil globs blocking part of the tubing. Be sure to perform an oil blowout before trying to vacuum a used system that has oil throughout the inside of the tubing. The oil blowout procedure does not necessarily blow oil out of the system but will blow the oil onto the inner walls of the tubes to allow you to pull a vacuum through the tubes. Video: same as #36 38. You can pull a vacuum with a one hose setup. With this setup, the vacuum gauge is mounted on the liquid line port and the vacuum is pulled from the vapor line port. However, this setup will take longer to pull a vacuum with than a two-hose setup because the metering device is found halfway down the tubing circuit which will restrict the flow of the vacuum. This is different than on a mini-split/ductless unit because with a mini-split, the metering device is in the outdoor unit, not half way down the refrigerant circuit. Video: 39. If you are concerned about water freezing inside the tubing of an air conditioner, keep a few things in mind. Heat within the tubing will be removed by the vacuum pump but this heat will be replaced with the heat surrounding the outside of the line set tubing. Also, the indoor blower motor can be turned on which will introduce heat from the air at the indoor evaporator coil. This reduces the possibility of water freezing during the vacuum procedure. This is only needed when vacuuming a system with a high water content in the tubing anyway. In most circumstances, when vacuuming AC and heat pump systems, the freezing of water is not something that will occur due to the amount of exposed copper tubing that can allow for an easy absorption of heat. You can prove that there is not a frozen water problem during the standing vacuum test if after 10 minutes with the vacuum pump off, the vacuum level does not rise. 40. With a 10 minute standing vacuum test, you can prove that no leaks, water, air, or nitrogen exist within the tubing and that the system is ready for refrigerant! To learn more about step by step procedures, check out our Book or E-book and test your knowledge with our 1,000 question workbook along with the answer key! We also have quick reference cards for use out in the field! Bundle Packs are a great way to save and get faster shipping! Check out our free quizzes to test your knowledge here! If you want to learn the full Total Superheat Charging Method, check out this article! If you want to learn the full Subcooling Charging Method, check out this article! If you want to learn about Delta T, check out this article! Tools that we use: Follow us on Facebook for Quick Tips and Updates here! Published: 7/22/2020 Author: Craig Migliaccio About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at & &
Adjusting the Airflow Speed on ECM Blower Fan Motors! (Variable & Multi-Speed Types)
In this HVAC training article, we will be discussing how to adjust the fan speeds on an indoor ECM variable speed blower motor and an ECM constant torque/multi-speed blower motor. These blower motor versions can be found in furnaces, air handlers, and packaged units. This is a follow-up to our other article on "Adjusting the Furnace/AC Airflow Speed on a 120v PSC Blower Motor". If you have not read that yet, I would encourage you to do so! To start, ECM stands for Electronically Commutated Motor which means that the motor is capable of electronically controlling it's own speed, and therefore CFM, according to the desired output. However, they are limited based on the total external static pressure (TESP) in the duct. ECM blower motors do not require an external capacitor to operate. Additionally, they can be identified by the presence of a removable module/bell on the end of the motor. The constant torque/multispeed motor will have the smallest module. Remember that CFM stands for Cubic Feet Per Minute. Roughly 400 CFM is needed for every 1 ton (12,000 BTU/HR) of Heat Removal Capacity in Air Conditioning Systems. Example: 1200 CFM is needed for a 3 ton 36,000 BTU/HR system. In humid climates, 350 CFM per ton can be selected in order to remove more moisture from the air. The BTU/HR capacity or tonnage of the air conditioning system should be included within the model number of the outdoor unit. This BTU/HR capacity should be used to set the CFM for the indoor blower motor. The blower speed for a gas heater is selected so that it is comfortable for the building occupant but also so that the Delta T (Temp Rise) does not continue to rise. If the Delta T continues to rise, this is due to low indoor airflow. Usually, gas furnaces have a temp rise of 50°F. Oil Furnaces may have a temp rise of 50-60°F. Remember that a heat pump in heating mode will need to run with roughly the same airflow speed as during AC mode even though it may not be comfortable for the building occupant. This is done so that the maximum amount of heat is gained in the building from the refrigerant. ECM Multi-Speed Blower Motor (Broad Ocean Type) For an ECM blower motor with wires exiting the module (shown above), the speed is changed at the control board by moving the colored wire terminals. Only 3 of the 5 colored wires may be used at a time. These three are connected to the "Cool", "Heat", and "Fan" terminals on the control board. The wires that are used will determine the speed settings that the motor will run at. Note: (High voltage is always going to your blower motor along with the common for the 24 volts. The remaining colored wires are the speed selectors for this blower motor.) On this motor module, the speed wires are red, orange, blue, yellow, and black. You will need to look at what the programmed speed designations are for M1/M2/M3/M4/M5 on the wiring diagram of the HVAC unit. It is important to know that you can’t go by a normal color code to determine the speeds. You need to follow the wiring diagram inside the HVAC unit. These blower motor speeds are programmed at the manufacturer's factory for the specific equipment model number unit it is installed in. The factory may only set two or three of these colors as actual speeds. The remaining colored wires will be default speeds. ECM Multi-Speed Blower Motor (Genteq X-13) The line voltage and 24v common are connected at the top and are labeled as C, L, G, N. The 24v common is C and the ground wire is G. For a 120v unit, the L is the 120v hot and the N is the 120v neutral. For 240v units, both the L and N are hots. These are not switched off but are live all the time. This X-13 model shown above designates the speeds taps as numbers, not as colors, to denote each speed. On the motor, only one of the 5 numbered taps has 24v power at a time based on the speed desired at the control board. When one of the taps is powered with 24v, the motor will turn on and run at the selected speed. In order to determine or change the speed, check the wiring diagram of the furnace/air handler/package unit that the motor is installed in. This will show what speed each numbered tap is programmed as. For example, on a package unit, only taps 3, 4 and 5 may be programmed. In other units, it may be 2, 3, and 4 that are programmed. After understanding what speed each tap is programmed for, we can make proper airflow adjustments. In the pictured example above, if the #5 speed tap is programmed for 1600 CFM and #4 is programmed for 1200 CFM and #5 is presently connected to the "Cool" terminal on the control board via the black wire, we know that the unit is running at around 1600 CFM as long as the TESP across the unit is not too high. If 1600 CFM is too high of an airflow volume and only 1200 CFM is needed because the system is a 36,000 BTU/HR air conditioner, we can swap the yellow with the black wire on the motor module. This will cause the "Cool" terminal on the control board to be connected to to the #4 terminal on the motor module via the black wire. This means that any time cooling is called for by the control board, 24v will be present on the #4 terminal of the motor module to turn the motor on and to run at roughly 1200 CFM. If the terminals are present at the motor module (ECM X-13) you can switch speeds at the blower motor location. If you have a plug instead (ECM Broad Ocean) you can only make the adjustment at the control board or at the plug terminals at the end of the wiring. Make sure power is off when doing any adjustment. You can verify the actual CFM by measuring the TESP of the system and comparing it to the manufacturer's airflow data sheet. Variable Speed Blower Motor ( Genteq 2.3, 16 pin connector) In the example above, an ECM 2.3 16 pin variable speed motor is connected to an air handler control board. Wires from the 16 pin plug are connected to this board. On this control board, there are multiple adjustments for the airflow speeds. These adjustments can be made by pulling the single wire connector and moving it to another single tab positioned horizontally in each row. The airflow adjustments on this board are pictured below. The following list refers to each adjustment starting from the bottom and moving upward. - The "Continuous Fan" refers to when the G terminal is powered for the fan only to run. -The "Blower-on and Blower-off delay" time period can be selected. -The "AC/HP CFM Adjust" is the airflow volume to be set for system, efficiency, comfort. -The "System Type" is the CFM per ton to be adjusted between low, normal and high. -The BTU/HR size is selectable between 48,000 42,000 36,000 or 30,000 BTU/HR -The "AUX Heat" makes sure that there is enough airflow when elect strip heat is called. Variable Speed Blower Motor (Genteq ECM 3.0, 4 pin connector) In the example of an ECM 3.0 with a 4 pin connector, the wires are not switched or moved to adjust the airflow settings. The control board is communicating with the blower module in order to determine the airflow volume needed. This control board is out of a variable speed furnace with a modulating gas valve that has a variable speed inducer motor. In this case, to adjust the blower speeds, move the dip switches (in the red section of the control board) to the positions shown in the manufacturer's installation instructions. The installation instructions for this furnace are needed in order to be able to know how to set these dip switches. If the instructions are not with the furnace, you can look up the model number of the unit and search for the installation manual via a google search. On this board, pins 3, 4, and 5 on the SW1/1 through SW1/8 dip switch block have to do with air flow. The continuous fan is marked SW3. The SW2 indicates the air conditioning size. Upon initial installation, these dip switches need to be adjusted for the particular unit, size, and application. To adjust the dip switches, turn the power off and take a flat head screw driver to lightly push the dip switches to the on/off desired position for each numbered switch. Match the positions to the desired pictures within the manufacturer's installation literature. In order to measure air flow you could use a flow capture hood, a rotating vane anemometer, or a hot wire anemometer. You could also use the Temp Rise Formula which you can learn about in our "HVAC Temp Rise Formula used to Measure Airflow CFM" video. I hope this helps you understand how to adjust the airflow speed on ECM Blower Motors! Be sure to check out our previous article on "Adjusting the Furnace/AC Airflow Speed on a 120v PSC Blower Motor" if you haven't read it yet! Also, if you are looking for a video to better help understand this topic, check out our "Adjusting HVAC Blower Speed CFM on Furnace & AC Units!" video below! If you want to learn about refrigerants and how they work in a system, check out our “Refrigerant Charging and Service Procedures for Air Conditioning” book . Test your knowledge with our 1,000 question workbook along with the answer key! We also have quick reference cards for use out in the field! Bundle Packs are a great way to save and get faster shipping! Check out Check out our free Quizzes to test your knowledge here! Check out our Free Calculators here! Tools that we use: Follow us on Facebook for Quick Tips and Updates here! Published: 05/19/2021 Author: Craig Migliaccio About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 16 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at & &
Adjusting the Furnace/AC Airflow Speed on a 120v PSC Blower Motor!
In this HVAC training article, we will be discussing how to adjust the fan speeds on an indoor PSC blower motor in furnace and air conditioning units. PSC stands for Permanent Split Capacitor and these motors can be easily identified by their direct connection to a capacitor. Remember that CFM stands for Cubic Feet Per Minute. Roughly 400 CFM is needed for every 1 ton (12,000 BTU/HR) of heat removal capacity in air conditioning systems. 350 CFM per ton can be used in humid climates to remove moisture from the air. The BTU/HR capacity or tonnage of the air conditioning system should be included within the model number of the outdoor unit. The blower speed for a gas furnace is selected so that the airflow is comfortable for the building occupant but also so that the Delta T (Temp Rise) does not continue to rise. If the Delta T continues to rise, this is due to low indoor airflow. Usually, gas furnaces have a temp rise of 50 F. Oil Furnaces may have a temp rise of 50-60 F. Remember that a heat pump in heating mode will need to run with roughly the same airflow speed as during AC mode even though it may not be comfortable for the building occupant. This is done so that the maximum amount of heat is gained in the building from the refrigerant. 120v PSC Blower Motor in a Furnace Always turn off power at the furnace or air handler before changing blower motor speeds on the control board. 120v PSC blower motors may come with multiple power wires that are color coded. The white wire is usually the common and the other colors are for separate speeds. You may ask, how do I determine which wire is the highest speed and the lowest speed on a PSC blower motor? This is done by taking electrical resistance measurements using a multimeter. In this example, we will be using a 120v PSC motor from a furnace. First, turn the power off to the furnace. Take a pic of where the blower motor wires are mounted. The white will be mounted to the common/neutral bar. Remove the blower motor wires from the control board or other connections. Place the red multimeter probe on the white common wire of the blower motor. Use the black multimeter probe to touch each of the other color-coded wires, one at a time. The electrical resistance from common to each speed is measured. In this example: The red and white measures 5.3 ohms. The yellow and white measures 4.3 ohms. The blue and white measures 3.3 ohms. The black and white measures 2.6 ohms. The resistance value of each pair changes, depending on the second wire selected. The second wire is the one other than the common in the pair. The color wire with the lowest resistance value is the highest speed. The color wire with the highest resistance value is the lowest speed. In the example above: Red= Lowest speed Yellow= Second from Lowest Blue= Second Highest Black= Highest Now that we have determined the speed of each of the color wires on the motor, we will look at a 120 volt furnace control board. On the board in this example, the white wire is connected to the neutral/common location. The blue wire is connected on the heat terminal. The black wire is on the cooling terminal. The other wires are connected on M1 & M2. The M1 and M2 can be referred to as spare/park and these terminals do not connect to any circuit on the board. They are simply a place to park the unused speed wire terminal ends so that they do not accidentally short against a ground while the system is running. In this example, in cooling mode the unit is running at its highest fan speed selected. If the heat speed needed to be changed to a slower speed, we would simply turn the power off to the unit and switch the blue with the yellow wire. Then we would turn the system on and check the temp rise in heating mode mode to make sure that it does not continually increase. I hope this helps you understand how to adjust the airflow speed on a 120v PSC Blower Motor! Keep an eye out for our article on adjusting airflow speed on ECM Blower Motors! Also, if you are looking for a video to better help understand this topic, check out our "Adjusting HVAC Blower Speed CFM on Furnace & AC Units!" video below! If you want to learn about refrigerants and how they work in a system, check out our “Refrigerant Charging and Service Procedures for Air Conditioning” book . Test your knowledge with our 1,000 question workbook along with the answer key! We also have quick reference cards for use out in the field! Bundle Packs are a great way to save and get faster shipping! Check out Check out our free Quizzes to test your knowledge here! Check out our Free Calculators here! Tools that we use: Follow us on Facebook for Quick Tips and Updates here! Published: 05/12/2021 Author: Craig Migliaccio About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 16 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at & &
An Additional Valve Core Removal Tool for your Vacuum Gauge! (Quick Tip)
Use an additional valve core removal tool in your vacuum setup to valve off and protect the vacuum gauge sensor from oil contamination when refrigerant is added into the tubing. If the sensor gets oil on it, the sensor will not perform correctly and the sensor will need to be cleaned. Often this is accomplished with rubbing alcohol but always follow manufacturers' instructions for cleaning. CPS Vacuum Micron Gauge - 1/4" Appion Valve Core Removal Tool - 5/16" Appion Valve Core Removal Tool -
Can I measure a Negative Subcooling When Checking the Charge? (Quick Tip)
The answer is no because the refrigerant rejects heat in the condenser so the pressure and temperature of the refrigerant should lower. The refrigerant starts off in the condenser as a superheated vapor and after it rejects heat, it changes from a vapor state to saturated. After it rejects enough heat, the refrigerant changes to a subcooled liquid. In this picture, we see a saturated temperature of 105°F and a line temp of 93°F. 105 - 93 = 12°F of Subcooling It is possible for the refrigerant to stay saturated instead of subcooling if the system is extremely low on refrigerant. A system that is very low on refrigerant may read 0-3 degrees of subcooling. Typically, there will be at least a small amount of subcooling measured. If the refrigerant is rejecting heat at the condenser, there is no way for the pressure or temperature of the refrigerant to increase as it makes its way through the condenser. It will either exit the condenser as saturated (saturated is liquid and vapor refrigerant in the same location) in a low refrigerant scenario or the refrigerant will be subcooled (subcooling is the lowering in temperature of the liquid refrigerant). If you are measuring negative subcooling, make sure your measurement locations are correct, otherwise you may want to recalibrate your tools! Be sure to check out the full Subcooling Charging Method Article here! Articles:
Ebook, Book, Workbook, Quick Cards:
Book, Workbook, & Cards:
Can you Braze Mini-Split systems instead of Flaring them?
I have been asked, “Can we braze mini-split systems instead of flaring them?”. The answer, technically, is yes. The only question is in a warranty situation, will the manufacturer accept an indoor unit with the flares cut off? In most cases, they should accept them and the manufacturer reps that I have spoken with have said that it is not a problem. However, technicians should verify this themselves with the manufacturer of the particular equipment that they install. Of course, when we braze copper line set, we make sure to flow nitrogen or another inert gas through the tubes so that oxidation does not occur inside the line set. The technician will still need to flare the connections to the outdoor unit since there are no stubs to braze, only service valves with flare connections. There is usually only one service port at the outdoor unit, and it is on the vapor service valve. This is where the nitrogen will be introduced. Make sure the small, liquid line is not connected to the flare connection on the liquid service valve. The nitrogen will exit out of this small, liquid line tube. Step by Step Process of Brazing Mini-Split Tubing: 1. The technician will begin by flaring the large suction line tube and connecting this to the outdoor unit. The small, line set tube should not be connected at this point but will remain open on the end. (The small line set tube would be referred to as the low pressure liquid tube since the active metering device is usually in the outdoor unit of a mini split system. This means that during cooling mode, the metering device will lower the pressure of the refrigerant before it enters the small line set tube.) 2. The flare connectors will need to be cut off of the indoor unit copper stubs and the copper tubes must be reamed in the downward position so that any small pieces of copper will fall out of the tube. 3. The copper stubs from the indoor unit should be swaged and the large and small line set tubes should be run into place and inserted into the swages. *Video on how to swage copper tube with every type of swaging tool* 4. Next, a flow regulator must be connected onto a nitrogen tank and set to flow at 2-3 CFH (cubic feet per hour). The nitrogen hose will then be connected to the outdoor unit vapor service port. The nitrogen will enter the vapor service port, flow through the large vapor line, through the evaporator coil, and out of the small line set tube near the small low pressure liquid service valve. The nitrogen will not pressurize the tubing but will push any oxygen out of the tubing during the brazing process. This will also help to dehydrate the lines prior to vacuuming. 5. The technician will then braze the swage joints using a small brazing tip and 15% silver brazing rod. The swage joints will either be behind the indoor head unit, inside the building (while the head unit is tilted upward to gain access to the underside of the unit) or outside the building if the stubs penetrate directly through the outside wall. Make sure to use a heat shield when brazing inside the building or outside near the siding. 6. The nitrogen will then be disconnected, and the small, low pressure liquid line will be flared and connected to the outdoor unit flare connection. Make sure to tighten all flare connections to the specified foot/lb torque value. Usually this is 12 ft/lb for ¼” OD copper tube and 27 ft/lb for 3/8” OD copper tube, but always follow manufacturers instructions to avoid future leaks or problems at the connections. 7. The system will then be ready for a pressure test to check for leaks. It’s okay to use flares as connections as long as you are sure they won’t leak. Below is a video on 10 reasons why flares may leak as well as ways to make sure that they won’t. Let me know your experience if you had to warranty an indoor mini-split head unit with cut off flares. I would love to know if anyone is having any trouble with a warranty based on the cut off flares and with which manufacturer. You can comment below or email me at , thanks! Check out our book “Refrigerant Charging and Service Procedures for Air Conditioning”. The full outline is available at If you have already purchased our book, be sure to tell local HVACR Instructors about our book and what you think of it. We would love to get the book into the hands of the next generation of HVACR Technicians! Published: 9/12/2019 Author: Craig Migliaccio About the Author:Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at &
Charging a System in a Dry Climate? Consider a TXV and Accumulator!
In a dry climate, certain considerations must be taken prior to installing or servicing air conditioning systems. A TXV metering device and an accumulator are important factors. In a dry climate, a TXV metering device should be installed instead of a piston metering device. Not only is this important for efficiency, the TXV will help protect the compressor somewhat during low indoor humidity and high outdoor ambient temps. The TXV does this by keeping the superheat steady at around 10-14 degrees instead of allowing the superheat to lower to 0 degrees. A superheat near 0 degrees will allow the compressor to get damaged by liquid refrigerant entering it. The accumulator is an important protection device as well and we will discuss this later in this article. When charging a system with a fixed orifice, the target superheat needs to be determined. The target superheat is a moving number so it will depend on the Indoor Wet Bulb Temp and the Outdoor Dry Bulb Temp. If you were to take an indoor WB and outdoor DB measurement in a dry climate, and line them up on a target superheat chart, you will likely see that the target superheat is not on the chart, meaning that the target superheat number for the system is too low to print (such as 5°F or lower). In that scenario, you must set a fixed orifice system at an inefficiently high superheat just in order to keep the compressor safe from having liquid refrigerant enter the vapor compressor. Liquid refrigerant entering a vapor compressor will damage it. Remember that if a system has superheat, the refrigerant entering the compressor will be in vapor form. If the system has no superheat, the refrigerant will be saturated (Saturated means that both liquid and vapor refrigerant exist in the same location) so the vapor compressor will get damaged by the saturated refrigerant entering it. Check out our full article on the Total Superheat Charging Method. Also, check out our video on the Total Superheat Method. A TXV will keep the superheat in the evaporator steady at a preset amount. Usually this amount is 10-14°F but you may read anywhere from 8-20°F when measuring total superheat on an air conditioning system. The TXV will not allow the superheat to lower unless the heat load is so low that the TXV cannot control the superheat anymore such as in a lower indoor airflow scenario. Remember that heat is stored in the air within a building and the job of the indoor blower motor is to move that heat across the evaporator coil in order for the refrigerant within the coil to absorb the heat from the air. The refrigerant then travels to the outdoor unit where it rejects the heat. To learn more about how air conditioning systems work, how to check the charge, and how to troubleshoot, check out our book (on our website or on Amazon). Sample pages are here! If the blower motor is broken, the TXV will not be able to hold the superheat steady because there is no heat load to work with. The TXV will still allow a small amount of refrigerant through while the system runs because it cannot shut the flow of the refrigerant off completely. However, in circumstances other than low airflow, the TXV can keep the compressor fairly safe from saturated refrigerant entering it as long as it is installed right and correctly working. Regarding efficiency, a TXV can reduce the heat load in a building faster than a system with a fixed orifice, if there is a high heat load in the building. Over average run conditions, a TXV will allow the system to gain a higher electrical efficiency and capacity due to the efficient removal of heat and humidity. This is because the TXV will make better use of the space inside the evaporator coil by varying the amount of refrigerant allowed into the coil. For all these reasons, a TXV metering device is a much better choice to install on a system than a fixed orifice. In locations with a dry climate such as in the state of Arizona, the positives for using a TXV grow even more, especially in terms of compressor safety. I can’t tell you how many times (it’s a lot) that I am asked about circumstances in which the target superheat calculated is 4 degrees or 0 degrees and what to do about it when checking the charge of a fixed orifice system. The answer is if you do not have a protection device such as an accumulator and you only have a fixed orifice, you would need to set the total superheat to a safer (higher) yet less efficient number for the sake of the compressor. Otherwise, the only other options are to switch the metering device to a TXV or to add an accumulator. I try to encourage those that are doing installations in these circumstances to include both the TXV and the accumulator in their new system installations. So what is the accumulator? The accumulator is a tank that stores saturated refrigerant and protects the compressor from liquid refrigerant entering in. If there is no superheat at the indoor coil due to a stuck open TXV or a fixed orifice during a low indoor WB and/or high outdoor DB scenario, the refrigerant will enter the accumulator tank as a saturated refrigerant and exit the tank as a vapor refrigerant. The accumulator is located directly before the compressor so no other change in the refrigerant state occurs after the refrigerant exits the tank or before the refrigerant enters the compressor. Systems that have a rotary compressor will automatically have an accumulator tank installed because a version of the accumulator tank is mounted onto the side of this type of compressor. In the case of a heat pump, these will automatically have an accumulator tank installed in them because of the possibility of the outdoor fins freezing during heating mode. An accumulator tank can be field installed on any system if it is suspected of having the possibility of low to no superheat. The accumulator will keep the compressor safe from saturated refrigerant. I know the addition of a TXV or an accumulator adds cost to a system install but these are crucial components that are needed on a system installed in a dry climate where low indoor WB and high outdoor DB temps are prevalent. The TXV will not only increase the safety for the compressor but for its small cost, it will increase the systems efficiency dramatically. TXV’s are also built much better than the older ones that we may find failing. This is due to the newer design of the stainless steel capillary tubing and stainless steel bulb that connect to the head of the TXV. TXV’s also make it extremely easy to check and set the system for an accurate refrigerant charge by using the subcooling method. To learn about the subcooling charging method click here for a full length article! If you want to learn more about all the fine details on charging methods and troubleshooting, check out our book which is available on our website and on amazon. The full outline and sample pages are available here. We have a 1,000 question workbook with an answer key that you can use to apply your knowledge as well. Check out our free quizzes to test your knowledge here! If you want to learn the full Total Superheat Charging Method, check out this article! If you want to learn the full Subcooling Charging Method, check out this article! If you want to learn about Delta T, check out this article! Tools that we use: Follow us on Facebook for Quick Tips and Updates here! Published: 6/11/2020 Author: Craig Migliaccio About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at & &
Checking the Charge of Air Conditioners without Measuring Pressure!
Can you check the charge on a system without checking pressure? Sure, remember that the only reason we check pressure is to convert it to saturated temperature. For single and two speed compressors systems, we use the subcooling and total superheat charging methods. I will briefly explain these charging methods using pressure before diving into reading temperatures only in order to check the charge. In order to measure subcooling, we measure the saturated temperature in the middle of the condenser coil. Normally, at the outdoor unit, we measure the pressure on the high side liquid port and convert this pressure to saturated temperature. Then we measure the temperature on liquid line within a few inches from the liquid port. Subcooling is the saturated temp minus the liquid line temp. In the example below, the subcooling is 5°F On the red gauge face in the picture above, the pressure measured is 318 PSIG. The pressure needle intersects at 100°F saturated temperature for R-410A. Therefore, the saturated temperature inside the condenser coil is 100°F. Calculate the subcooling based on the picture: Sat Temp - Actual Liquid Line Temp= Subcooling 100°F - 95°F = 5°F of Subcooling In order to measure total superheat, we measure the saturated temperature in the middle of the evaporator coil. Normally, at the outdoor unit, we measure the pressure on the low-side vapor port and convert this pressure to saturated temperature. Then we measure the temperature on vapor line within a few inches from the port. Total superheat is the temp on the line minus the saturated temp. In the example below, the total superheat is 15°F. On the blue gauge face in the picture above, the pressure measured is 118 PSIG. The pressure needle intersects at 40°F saturated temperature for R-410A. Therefore, the saturated temperature inside the evaporator coil is 40°F. Calculate the total superheat based on the picture: Actual Vapor Line Temp – Saturated Temp = Total Superheat 55°F - 40°F = 15°F of Total Superheat There is a difference between a superheat measurement and a total superheat measurement. A total superheat measurement is taken at the outdoor unit, whereas a superheat measurement is taken at the indoor coil. Total superheat includes any change in the superheat from where the refrigerant exits the indoor coil until it enters the outdoor unit. Below are examples of superheat and total superheat. Superheat is shown in the picture below. 54°F - 40°F = 14°F of superheat Total superheat is shown in the picture below. 55°F - 40°F = 15°F of total superheat If you want to learn more about the refrigeration cycle, check out this video: If you want to learn more on the complete total superheat method, read this article. If you want to learn more on the complete subcooling charging method, read this article. Getting on with it! Now that we have covered what is normally done to measure both subcooling and total superheat, let's explain how to measure the saturated temperature without measuring pressure. Let’s start with subcooling. In order to determine the saturated temperature in the middle of the condenser coil, we need to figure out where to take our measurement. We must attach our temp sensor onto the condenser coil tubing in a location where the saturated refrigerant is located and where there is not much air moving through which could affect our temp measurement. The picture below shows the refrigerant changing as it moves through the outdoor coil. As the refrigerant enters the condenser coil, it is a high temp superheated vapor. As it moves through the tubing, the refrigerant changes to being saturated. Next, the refrigerant subcools. In the example below, the high temp superheated vapor is 170°F. The saturated refrigerant is 105°F, and the subcooled liquid exiting the condenser is 93°F. In the example above, you see that the refrigerant is in the saturated state at 105°F during the majority of the time while traveling through the coil. Now let's look at where to find this location in real life. Below, you will see several pictures of the inside of an outdoor unit. In this case, the compressor is wrapped with a black sound shield. Note where the tubing is exiting the compressor and entering the condenser coil. Also note where the tubing is exiting the coil and then exiting the outdoor unit on the small liquid line. On the coil of this unit, the high pressure superheated vapor from the compressor is distributed into the coil in multiple locations. The subcooled liquid is also collected in multiple locations. Between where the superheated vapor enters the coil and where the subcooled liquid exits the coil, we see three elbows in most of the areas and two elbows in one area. This may be different from unit to unit that you work on. If a temp sensor was mounted to the middle elbow, this would be where the saturated state is located. Insulation can also be mounted to the outside of the sensor to make sure that the measurement is accurate. My favorite tool to take temperature measurements with is the ST4 digital dual temp meter equipped with k-type bead temp sensors: K-type bead temp sensors can be taped onto the tubing to get an accurate temperature reading. Clamps can also be used but for small locations, I find k-type bead temp sensors work best. Bead temp sensors are so small that they can even be pushed through a hole made by a zip screw, if needed. In this example, while this system was running, the temp on the elbow for the saturated refrigerant measured 92.2°F. The actual temp on the liquid line read 84.9 . To find the subcooling: 92.2°F sat temp - 84.9°F line temp = 7.3°F subcooling. Another way to find the location of the saturated refrigerant is to look down through the top of the outdoor unit in order to find and count the elbows between the superheated vapor and the subcooled liquid refrigerant on the condenser coil. Then place a temp sensor between the fins on the tubing in the correct spot where there is a lower amount of air crossing the fins. In this example, while this system was running, the temp measuring the saturated refrigerant read 87.5°F. The actual temp on the liquid line read 82.6 . To find the subcooling: 87.5 sat temp - 82.6 line temp = 4.9°F subcooling. This actual subcooling would need to be compared to the target subcooling found on the outdoor unit rating plate. If the actual subcooling is lower than the target subcooling, add refrigerant. If the actual subcooling is higher than the target subcooling, recover refrigerant. Now onto superheat and total superheat! At the evaporator coil, the refrigerant enters the metering device as a high pressure, subcooled liquid. The refrigerant exits the metering device as a low pressure, 80% liquid 20% flash gas mix. Because the refrigerant becomes saturated immediately after exiting the metering device, it is easy to locate the section of tubing where the refrigerant is saturated. As you can see in the animated picture below, the temperature of the saturated refrigerant as it enters the evaporator is the same as where the refrigerant has traveled halfway through the coil. In this example, the refrigerant remains 40°F until the refrigerant changes completely into a vapor and starts to increase in temp. We see on this coil that the there is a 54°F line temp - 40°F sat temp = 14°F superheat. In order to mount the temp sensor on the evap coil in the location of the saturated refrigerant, the evap coil box cover will need to be removed. Between the metering device and the coil are distributor tubes connecting to multiple locations on the coil. Usually, the distributor tubes connect at the bottom of the A-coil. This is where the low-pressure refrigerant enters the coil. The superheated vapor refrigerant exits at the top of the A-coil. The temp sensor can be mounted anywhere from the first tube elbow to about halfway up the coil as long as the elbows are all in the same line and not going in a different direction. The temp measurement will also be more accurate if the bead temp sensor is insulated around the mounting location. In the example below and to the left, if the temp on the elbow inside the evap coil measured 40°F and the temp on the vapor tube on the outside of the coil measured 51°F, the superheat would be 11°F. 51°F - 40°F = 11°F superheat In the example below and to the right, if the temp on the elbow inside the evap coil measured 40°F and the temp on the vapor tube at the outdoor unit measured 52.9°F, the total superheat would be 12.9°F 52.9°F - 40°F = 12.9°F total superheat As you can see, it is fairly difficult to locate and mount a temp sensor to the tubing which carries the saturated refrigerant. There is also the possibility of mounting the temp sensor in the wrong spot accidentally. In reference to checking subcooling at the outdoor unit, there may be some units that have an access panel that can be taken off for easy access into the inside of the unit. However, in most cases, there is no easy access door. The easiest access is to take off the top grille and condenser fan. We would want to avoid moving objects like the condenser fan just to take a simple measurement. It would be great if a manufacturer provided us with a simple temperature measurement spot to measure the high side sat temp but up to this date in time, no manufacturer has taken the step to provide us with one. Maybe someday this will be considered. I look forward to that day but for now, you can see why we find it easiest to just measure pressure to find subcooling. Also, if the unit was severely undercharged or overcharged, the location on the tubing at the outdoor unit where the saturated state could be found may change. We know where the location is with an average refrigerant level in the outdoor unit but with a severe case, this could cause confusion for the technician if only one specific elbow temp was measured. At the indoor coil, it may be slightly easier to locate and measure the saturated temp to determine superheat and total superheat, but it is usually still not worth the time and effort it would take to mount the sensor. Another point that must be considered is that we usually check total superheat and subcooling at the same time. When using the subcooling method, we also measure the total superheat to make sure that the TXV is controlling the superheat properly. Most techs try to avoid measuring pressure to avoid contaminating the system with old oil which may be leftover in the refrigerant hoses of their manifold gauge sets. That is why quick connect test gauges and electronic test probes have grown in popularity. These tools provide a quick access to measure pressure without needing to fill long hoses just to read pressure. Wireless test probe links: Fieldpiece Wireless 6 Piece Job Link System Probe Kit JL3KH6 - Testo Wireless Smart Probe Full Kit - Quick connect test gauge links: Blue Vapor Gauge- Red Liquid Gauge- Quick Coupler for the Gauges- ST4 Dual Temp Meter- If you want to learn more about all the fine details on charging methods and troubleshooting, check out our book which is available on our website and on amazon. The full outline and sample pages are available here. We have a 1,000 question workbook with an answer key that you can use to apply your knowledge as well. If you want to learn about Delta T, check out this article! If you want to learn the full Total Superheat Charging Method, check out this article! If you want to learn the full Subcooling Charging Method, check out this article! Check out our free quizzes to test your knowledge here! Tools that we use: Follow us on Facebook for Quick Tips and Updates here! Published: 7/16/2020 Author: Craig Migliaccio About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at & &
Checking the Charge of a Mini-Split Unit!
A question that I get asked frequently is “Can I check the charge of a mini-split ductless unit with superheat and subcooling the same way I do on a conventional air conditioner or heat pump?". The answer is not exactly, but you can do some troubleshooting. A mini-split differs from a standard central air conditioning system in a variety of ways. Conventional split systems usually have a TXV (Thermostatic Expansion Valve) or a piston metering device, a single or two speed compressor, a single or two speed condenser fan, and a multi-speed indoor blower motor. The speed of the condenser fan and the indoor blower match the heat removal capacity of the compressor speed during air conditioning mode. The same goes for during heating mode. In most cases, on standard split systems, we are dealing with a single speed compressor with a single speed condenser fan and a fixed speed on the indoor blower motor. This means that the system is always running at a constant known speed and capacity. Most current mini-split systems are VRF (Variable Refrigerant Flow). These systems include an EEV (Electronic Expansion Valve), a DC inverter compressor along with a DC powered condenser fan and DC powered indoor blower motor. Because all these components are powered with DC voltage, they can all be ramped up and down in capacity by the main control board. The control board uses temperature and sometimes pressure sensors in a variety of locations in order to control the operation and safeguard the system. A mini-split system may be equipped with one indoor head unit or multiple indoor head units. When there are multiple indoor head units and the piping is directly mounted from each of the indoor head units to the outdoor unit, there is an EEV for each head unit in the outdoor unit. Regardless whether there is one EEV for a single indoor head system or there are two EEV’s or more for a multi head indoor unit, there is usually a temp sensor mounted by the manufacturer on both sides of each EEV, even if the sensor is a little distance away. The system will also have other temp sensors as well. The temp sensors are monitoring the compressor discharge temp, the saturated refrigerant temp in both coils, and the temp on the refrigerant lines exiting both the condenser and the evaporator coil. The EEV will not only adjust for an efficient superheat but it will also maintain a steady range of vapor pressure depending on the conditions. This means that if you hook your pressure gauge onto the available vapor line port, it will give you a vapor pressure that you can’t do much with because you don’t know exactly what vapor pressure the system is targeting at that moment in time. However, if the pressure converted to saturated temperature is below 32°F, this would signal a problem and eventually a frozen evaporator coil. Now that we know that a VRF mini-split ramps up and down in refrigerant flow and heat removal capacity, let’s move back a bit and talk about a fixed speed system. A properly charged system in air conditioning mode with a standard single speed compressor and a TXV which has correct airflow and no other problems, will usually operate with roughly 8°F to 15°F of subcooling and roughly 8°F to 15°F of superheat. You can determine the exact target subcooling based on the target subcooling posted on the outdoor unit rating plate or under the outdoor unit shroud. The TXV will usually hold the superheat around 10°F to 14°F but it may fluctuate to around 8°F to 17°F depending on the conditions. We know this to be the case in systems that have a single speed compressor with a fixed airflow speed at the indoor and outdoor unit. (To learn more about subcooling and target subcooling, and measurement locations, read this article. To learn more about superheat, total superheat, and target superheat, and measurement locations, read this article.) However, a VRF mini-split in air conditioning mode will ramp up and down the speed of the compressor, the indoor and outdoor fans, as well as the volume of refrigerant moving through the EEV. To get a useful measurement from a mini-split, we must lock it in full speed air conditioning mode. Sometimes this is called emergency operation or full air conditioning speed. You will notice on most mini-splits, there is only one vapor port and no liquid port on the outdoor unit service valves. Sometimes there will be one main vapor port even if there are multiple indoor head units. On other outdoor units, there will be one vapor service port for every indoor head unit. The biggest reason that you don’t see a liquid service port on the outdoor unit is because on a mini-split, the EEV is mounted inside the outdoor unit. Therefore, if you had a port on the liquid service valve, you would be measuring the low pressure exiting the EEV. This will be roughly same pressure as the saturated refrigerant in the middle of the evaporator coil. (This is also why you see the liquid line is insulated as well as the vapor line on mini-split units. Both low temperature lines will attract humidity and absorb heat if there is no insulation on this line set tubing.) A liquid pressure measurement at the liquid line service valve wouldn’t be useful to calculate subcooling and no manufacturer wants you to get confused so no port is mounted there. Some outdoor mini-split units have a liquid service port mounted inside the outdoor unit, underneath the outdoor unit shroud, prior to the EEV(s). This can be used for troubleshooting to determine if there is at least some subcooling prior to the refrigerant entering the EEV(s) but because the manufacturer does not provide us with a target subcooling, this port is not necessarily used to check the charge. Now we are getting to the good stuff. A VRF mini-split is locked in emergency cooling via a button on the indoor head unit, a dip switch or control program, or when the temperature on the thermostat is turned down very low in temp along with the high fan speed setting and after a time requirement, the unit will run at full capacity. Each unit is a little different. You will notice that a VRF mini-split running at full capacity during cooling mode will generally have a higher Delta T than a conventional single speed split unit. Delta T is the change in temp across the evaporator coil. Delta T will also depend on the heat load in the building, including the humidity. Keeping that in mind, usually during average humidity and temperatures, the Delta T of a mini-split may average 20°F to 24°F instead of 18°F to 21°F on a single speed unit. (For more information on Delta T, make sure to check out our article on it!) This is because a mini-split will run at a lower superheat across the evaporator coil. This means that there is more saturated refrigerant in the coil to absorb the heat load. Usually on a single speed system, we are worried about maintaining a good total superheat so that the compressor does not have saturated refrigerant entering it. However, on most mini-split units running at full cooling capacity, the total superheat measured at the outdoor unit will typically be between 0°F to 5°F. Often times it is right in the middle at 2°F or 3°F. Remember that if superheat is present on the vapor line where the refrigerant enters the compressor, then we know that the refrigerant is no longer saturated but is fully in the vapor form. The vapor compressor must only have vapor refrigerant enter it or it will become damaged. (To learn more about superheat, read this article.) How can a mini-split system run with 0°F of superheat and not kill the compressor you ask? A mini-split has a rotary style compressor which always has a type of accumulator mounted to it’s side. This would be considered an accumulator with a vaporizing screen inside. Prior to that in the refrigerant circuit, may be another accumulator. This second larger accumulator’s job is to store extra refrigerant when it is not needed. Remember that the system will ramp up and down in capacity depending on the need. Also remember that unlike a single speed system, a mini-split comes with enough refrigerant for a range of line set length. Because there is a range of line set length, this equates to a range of total refrigerant weight that is allowed in the system while still being able to operate correctly. The amount of refrigerant is usually not an exact amount like in a single speed system due to this range. Getting back to our point though, an accumulator’s job is to store saturated refrigerant and it only allows vapor refrigerant along with a little bit of oil to exit the accumulator and to enter the compressor. (To learn more about the accumulator, check out this video.) Because an accumulator will only allow vapor refrigerant to exit the tank, the vapor compressor will be safe from liquid or saturated refrigerant entering in. Because most larger mini-splits have two accumulators and the last one right before the compressor inlet includes a vaporizing screen, the compressor is very safe as long as the system is not severely overcharged. Smaller mini-split units may just have the one single accumulator with the vaporizing screen which is mounted on the side of the compressor. If there is only one accumulator present, this single accumulator will typically be larger in size and will be enough to protect the compressor except if the system is severely overcharged. During emergency cooling mode, remember that it must be above 70°F indoors and outdoors before taking any measurements and the system must be running for at least 10 minutes. A total superheat of 0°F to 5°F, a saturated temperature above 36°F, and a Delta T of 20°F to 24°F is a very good indication that the system is charged properly. However, this does not mean that we should charge a system that is low on refrigerant to these numbers. These are merely common indicators that are seen on systems with an accurate charge and this should not be mistaken as a charging method. Remember that targeting a certain vapor pressure is futile because the system is monitoring the vapor saturated temperature constantly and is adjusting the EEV for an optimal vapor pressure and superheat. Of course, if you notice a vapor pressure converted to saturated temperature that is below 32°F, then there is likely a problem such as low refrigerant charge, liquid line restriction or low indoor airflow. You can notice low airflow right away by measuring the CFM (Cubic Feet Per Minute) using a rotating vane anemometer at the indoor head units and comparing that to the BTU/HR capacity of each head unit. You are looking for roughly 400 CFM per 12,000 BTU/HR of capacity but 350 to 425 CFM will still work. If you have an available liquid port inside the outdoor unit, you can check subcooling. If the subcooling is very low such as 1°F or 2°F, the system is low on refrigerant if you are running at full capacity cooling mode. Remember that you cannot see the amount of refrigerant that is in each accumulator and you don’t want to overcharge the system to predetermined pressures or temperatures that you have in your mind. Some manufacturers may provide certain pressure and temperature specifications along with an average compressor current, but this is usually a rare occurrence. Remember that if your superheat is a little higher than 5 degrees, maybe 5 to 10 degrees, it may not mean that the system has a problem such as a low refrigerant charge. There are many sensors and settings on these mini-split units and you don’t want to take the approach of just adding more refrigerant to see if the system will work better or be closer to certain standards that you would like to see. If you overcharge the unit a bit, the unit may not allow itself to run at full cooling capacity because of a high compressor current or high discharge temp. Just because you see an EEV hunting by reading the total superheat, it doesn’t mean that the unit is low on refrigerant. It could mean that the unit is overcharged so don’t just add more refrigerant to the system! However, if during emergency cooling mode, the superheat is 15°F, 20°F, or higher, the unit may be low on refrigerant or have a liquid line restriction. An example of a liquid line restriction could be an EEV that is not opening up enough maybe due to corrosion between the valve coil and the valve body affecting the magnetic field and therefore not allowing the inner stem to turn to open the inside of the valve. If the system has a liquid line restriction, it would not be wise to add refrigerant to the system thinking it was low on refrigerant. In the example below, we see an R-410A saturated temperature of 27°F and a vapor line temp of 56°F. Total Superheat = Actual Vapor Line Temp - Sat Temp Total Superheat = 29°F so there is a problem such as one of the following: low refrigerant charge, low airflow, or liquid line restriction The best thing to do on a mini split system that is not working properly or is thought to have a low refrigerant charge is to search for leaks. Look for oil stains where refrigerant and oil have seeped out. Apply bubble leak detector at the joints, and/or use a refrigerant leak detector such as the ultrasonic leak detector to find the leaks. (Here are links to these products: bubble leak detector, ultrasonic leak detector) Then recover the refrigerant, fix the leaks, pressure test, vacuum, and weigh in the total amount of refrigerant needed for the system. Breaking the vacuum with the correct amount of refrigerant needed for the system is referred to as the “Total Weight Method”. The total weight of refrigerant needed is usually posted on the outdoor unit rating plate and is listed as the “factory charge”. This includes the amount of refrigerant needed for the outdoor unit, the indoor unit(s) and a specified length and size of line set. Additional refrigerant weight may need to be added for line set that exceeds the total cumulative length stated on the outdoor unit rating plate. Remember that if you think the system has an electrical based problem, it may just be undercharged or overcharged and the system is compensating for that incorrect charge. Once you know that the correct amount of refrigerant is inside the unit, you can confidently troubleshoot the problem but often, the problem goes away because it was an incorrect refrigerant charge to begin with. If you notice a severe electrical problem or communication issue instead of a capacity issue, then yes, look at and troubleshoot the electrical components. The total weight method is the recommended charging procedure for verifying the refrigerant level in a unit. If the unit is new, it will have the factory charge already inside and the refrigerant will be held back by the service valves. You can open the service valves after pressure testing, vacuuming, and performing the standing vacuum test. If additional refrigerant needs to be added to the system due to an extra long line set run, break the vacuum with the correct amount of refrigerant from the bottle by using an electronic scale. (Here is a link to an electronic scale.) After breaking the vacuum with refrigerant from the bottle, open the service valves. Here is a Total Weight Method example: On the rating plate, the R-410A system lists the factory charge as 4lbs 4oz. The rated cumulative line set length for this factory charge is 25’ to 90’. (Cumulative means that if there is more than one head unit, add the line set lengths for each head unit together to equal the cumulative length.) If the actual cumulative length was measured to be 125’, you would need to add enough refrigerant for 35’ worth of line set. 125 - 90 = 35’ The unit says to add 1.08 oz for every 5’ of additional line set added. 35 / 5= 7 7 x 1.08 oz = 7.56 oz additional refrigerant needed Check out our Total Weight Method article including examples and the refrigerant weight chart by clicking here: Check out our Quizzes to test your knowledge here! Follow us on Facebook for Quick Tips and Updates here! Published: 5/6/2020 Author: Craig Migliaccio About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at & &
Clogged Liquid Line Filter Drier?
How can you tell if you have a clogged liquid line filter drier? If there is a noticeable temperature drop from one side of the filter drier to the other, this means that there is a pressure drop. Remember that temperature follows pressure and temperature is something that we can measure on the outside of the tubing. Usually no ports are available at the inlet or outlet of the liquid line filter drier. Filter driers are designed to have an extremely low pressure drop across them even while filtering down to 25 microns and trapping both moisture and acids. On most residential systems with a newer filter drier, the temperature drop may be around .5 degree temp drop or less from one side to the other. Often, this occurs because of the large surface area of the filter drier itself exchanging heat with the surrounding air and not due to any pressure drop. It is hard to pinpoint an actual number to say that this means that there is a clog in the filter drier. However, if you do measure the correct subcooling at the outdoor unit, a high total superheat, a low delta T at the indoor coil and there is a few degree temperature drop across the filter drier, then figure on replacing the filter drier! In the example above, the R-22 system has a low side sat temp of 22°F and a vapor line temp of 66.7°F Total Superheat = Vapor Line Temp - Low Side Sat Temp Total Superheat is 66.7 - 22 = 44.7°F In the example above, the R-22 system has a high side sat temp of 97°F and a liquid line temp of 82.6°F Subcooling = High Side Sat Temp - Liquid Line Temp Subcooling is 97 - 82.6 = 14.4°F Because the system in the previous two pics has a high superheat and a normal to high subcooling, this signals that the system is not low on refrigerant and actually has some type of restriction in the liquid line. To tell the difference between a low refrigerant charge and a clog in the liquid line, the technician will need to measure the subcooling. If the subcooling is correct or high while the superheat is high, this means that there is a liquid line restriction problem. If the subcooling is low and the superheat is high, this means that the refrigerant charge is low. If it is determined that there is a liquid line restriction, the technician must investigate to determine which component is the problem on the liquid line. We usually start by measuring the temp drop across the filter drier. If the filter drier is partially clogged, there may be a few degree temp drop across it. However, if the filter drier is completely clogged, there will be a large temperature drop across it and likely frost due to the low temp of the refrigerant exiting the clogged filter drier. Remember that if there is a temp drop across the filter drier, the liquid refrigerant is being restricted and partially flashing to a gas before making it to the metering device. The metering device is the restriction that should control the pressure drop and expansion of the refrigerant. A restricted filter drier will not allow enough refrigerant to get to the metering device. The clog will also not allow the refrigerant to be in the subcooled state as the refrigerant enters the metering device. Because of this, there will not be enough refrigerant exiting the metering device and entering the evaporator coil in order to absorb the heat from the air crossing the outside of the coil. This will always result in a high superheat at the evaporator coil. Even if the filter drier is not the problem, remember to always replace it any time another refrigerant based component is replaced! The filter drier has a limited capacity for water storage so it should always be replaced any time the system is opened to atmospheric pressure. After recovering the refrigerant or pumping down the system, make sure to cut the filter drier out instead of sweating it out with a torch. Heating the old filter drier will result in the moisture within the filter drier to boil out, escaping into the system's tubing. You can avoid this by simply cutting out the old brazed-in-filter-drier and brazing in a new one. Other types of filter driers can be replaced with different methods. Some have flare connections and larger commercial filter driers have a replaceable core so that the replacement of the outer shell is not needed. To learn more about troubleshooting liquid line restrictions, check out this video below! Also check out our book for a full guide of troubleshooting scenarios while measuring the refrigerant charge! To learn more about step by step procedures, check out our Book or E-book and test your knowledge with our 1,000 question workbook along with the answer key! We also have quick reference cards for use out in the field!
Bundle Packs are a great way to save and get faster shipping! Check out our free quizzes to test your knowledge here! Check this article out on Liquid Line Restrictions! If you want to learn the full Total Superheat Charging Method, check out this article!
If you want to learn the full Subcooling Charging Method, check out this article!
If you want to learn about Delta T, check out this article! Tools that we use:
Follow us on Facebook for Quick Tips and Updates here!
Published: 8/19/2020 Author: Craig Migliaccio About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at & &