When Installing or Replacing an Air Conditioner, Use These Procedures for the Refrigerant Tubing!
When installing a new HVAC system, replacing an existing HVAC system, or just replacing one part of the system, there is a sequence of procedures that must be performed for the refrigerant tubing to prepare for refrigerant. When replacing an existing system, start at Procedure 1. When installing a new system, start at Procedure 2. Remember, under US federal guidelines, technicians must be EPA 608 certified before handling refrigerants. Procedure 1, Recover or Pump Down: In order to open an existing system to atmospheric pressure (0 PSI) for service, first recover all of the refrigerant or pump down the refrigerant into the outdoor unit. After a system is pumped down, all the refrigerant is trapped in the outdoor unit behind the service valves and in front of the service valves the pressure is 0 PSI. We usually only pump down the refrigerant into the outdoor unit if the outdoor unit is going to be reused in its current condition. Recovery and pump down guidelines are found in the EPA Section 608. Presently, per these guidelines, high pressure R-22 or R-410A appliances must hold a vacuum level of 0 PSIG or lower after recovery or pump downs of systems with less than 200 lbs of refrigerant. Typical residential systems have 3 to 15lbs. (I usually try to recover or pump down to 4”hg unless there is a leak.) Do not pump down a unit with a Scroll compressor because the refrigerant acts as insulation to separate the electrical motor windings from the ground frame inside the hermetic compressor. In the case of reusing a unit with a scroll compressor, just shut the service valves and recover the rest of refrigerant in the line set. This is done so that the motor does not get damaged due to shorting to the ground frame. Recovery Video - https://youtu.be/os9gKLf7LJg Procedure 2, Valve Core Removal: A split system is usually shipped with the service valves in the closed position, with refrigerant trapped in the outdoor unit, and with no pressure at the access ports. Valve cores (otherwise known as "Schrader Valves") are located at the service access ports. The valve cores (if equipped) should be removed from the ports prior to brazing the copper tubing at the service valves. This is done so they do not melt or become damaged during the soldering or brazing process. (For best results, valve cores remain out until after all the procedures are done and refrigerant is in the unit. Make sure to use valve core removal tools during or after the pressure test and moving forward through the procedures.) Procedure 3, Brazing or Silver Soldering: The line set must be brazed, silver soldered, or connected with another method such as crimp fittings or flares. When brazing, use 15% silver brazing rod and flow inert gas such as nitrogen through the tubing to reduce oxidation inside the tube. Nitrogen should flow through the tubing at 3 CFH. There should not be any pressure within the tubing. The nitrogen is just purging the air while heating the tubing for the braze rod to melt and seal the joint. Use an air acetylene or oxy-acetylene torch for high temp brazing. Use a propane or Mapp gas torch for silver soldering. When silver soldering, use Stay-Brite 8 and flux. Use the least flux possible because flux is acidic and you do not want acid inside the tubing. When silver soldering, there is no need to flow nitrogen because the tube is not hot enough to create oxide. However, when brazing, no additional flux is required. the phosphorus in the braze rod acts as the flux so no acid enters the tubing. Brazing at the Service Valves Video: https://youtu.be/GgBvzGhoesI Brazing at the Evap Coil Video- https://youtu.be/7G1tj7KgdBk Procedure 4, Pressure Testing: The system must be pressure tested for leaks. The pressure must be less than the max design pressure as stated on the low side rating plate. If the system is not new then make sure to only pressure test to a lower number, otherwise leaks will form due to the high test pressure. Nitrogen is held in the system for at least ten minutes to see if the pressure reduces, indicating a leak. Bubble leak detector or an ultrasonic leak detector is used to find any leaks. Remember that pressure testing with a digital gauge set will allow you to see a decrease in pressure faster and more accurately than a compound manifold gauge set. Pressure Test Video- https://youtu.be/2REIP5Ddn60 Procedure 5, Oil Blowout Procedure: If part of the system is existing and not new, an oil blowout procedure may be needed. If you are having a problem with the vacuum due to a glob of oil closing off the inside of the tubing, perform the oil blowout procedure. Run 100 psi of nitrogen for 5 seconds through the liquid line port and out the vapor port to blow the oil onto the inner walls of the tubing in order to allow a vacuum to be pulled through the tubing. Vacuum problems including Oil Blowout Video- https://youtu.be/Ks3MtPmXDUE Procedure 6, Vacuuming: A vacuum is usually pulled from both ports of the system. Vacuum rated, valve core removal tools should be used at each port along with another valve core removal tool for valving off the vacuum gauge, if needed. The vacuum must reach below 500 microns before isolating the pump from the rest of the vacuum setup. (I typically target 200-300 microns). Vacuum Video, Steps 6-10 https://youtu.be/wYZ8Wudksb0 Procedure 7, Standing Vacuum Test: The Standing Vacuum Test is performed by valving off the vacuum pump and then powering off the vacuum pump. The vacuum gauge is still connected to the system and reads the true vacuum level. The vacuum level may initially rise as the vacuum equalizes across the tubing but then it should remain stable. This initial rise may only be 100 microns or less. If the vacuum level does not rise above 500 microns after 10 minutes, this indicates that the system does not have leaks, water, nitrogen, or air left in the system and it is ready for refrigerant. The standing vacuum test (otherwise known as a decay test) is held for 10 minutes. This vacuum level may not rise at all if valve core removal tools are used. Procedure 8, Valve off the Vacuum Gauge: The vacuum gauge is valved off so that oil and refrigerant do not contaminate the vacuum sensor for future use. Procedure 9, Break the Vacuum with Refrigerant from the Bottle or System Valves: The vacuum is broken by adding refrigerant from the bottle into the liquid line or by opening the service valves allowing refrigerant from the outdoor unit into the line set. Vacuuming, Breaking the Vacuum with Refrigerant, Checking the Charge- https://youtu.be/PfdL3kZ3C6I Procedure 10, Install The Valve Cores: The valve core removal tools are left on the ports before brazing, through pressure testing, through vacuuming and they are used to replace valve cores after the system is at positive pressure. If valve cores are left in during the vacuum process, a deep vacuum may not be able to be pulled due to the restriction. After replacing the valve cores, test to see if the valve core is leaking before removing the tool. Procedure 11, Attach Port Caps or the Gauge Set: Either install the caps onto the ports or add a gauge set to check the charge. To add more refrigerant into the unit, the system must be running so that the pressure in the bottle is higher than the pressure on the vapor port. This will allow the refrigerant in the bottle to travel into the unit. Make sure to use a refrigerant scale as well. If the manifold gauge set is used to check the charge, make sure to test the valve cores for leaks after disconnecting. Caps are installed upon completion. Vacuuming, Breaking the Vacuum with Refrigerant, Checking the Charge- https://youtu.be/PfdL3kZ3C6I Adding R-410A Refrigerant Video- https://youtu.be/OSpfBXhk0nQ 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 www.acservicetech.com/store Check out our free Quizzes to test your knowledge here! Check out our Free Calculators here! Tools that we use: www.amazon.com/shop/acservicetech Follow us on Facebook for Quick Tips and Updates here! Published: 06/09/2021 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 https://www.acservicetech.com & https://www.youtube.com/acservicetechchannel & https://www.facebook.com/acservicetech/