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40 Vacuum Tips for HVACR Technicians! Avoid Frustration!

Updated: Nov 20, 2023

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!


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.

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.

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:


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.

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.

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.

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.

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!

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Check out our free quizzes to test your knowledge here!

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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 & &


2 comentários

Daniel Wickham
Daniel Wickham
5 days ago

The vacuum service provided by the HVAC Contractor Palm Beach company was outstanding. The technician arrived on time, was very professional, and explained the entire process to me. They took great care in cleaning every part of the system. I can already feel the difference in air quality.


Your tip on closing and reopening the valve core removal tool during a vacuum works. Doing this immediately lowered the micron reading from about 750 microns to under 500 microns while I was evacuating a recovery tank. Here are a couple of tips on the subject. (1) I was able to clean and restore the sensor in a non-working Supco micron gauge using Paslode electric tool cleaner. I squirted the Paslode into the port and let it sit upright overnight and then did it twice more. It now reads very close to my BlueVac micron guage. (2) I have a Robinair 15600 that I didn't use for a few years. I tested it blanked off and it would not pul…

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