Commercial installers of our kits as well as professional, licensed air conditioning repair facilities have asked, so we have developed a procedure and an eight-point checklist to be followed for charging a FIXED-DISPLACEMENT COMPRESSOR (Sanden style) system with 134a REFRIGERANT from a CHARGING STATION. (Note: procedures are different if you are HAND CHARGING with individual refrigerant canisters or if you are NOT using 134a refrigerant).
Many aftermarket classic car air conditioning systems, including our Perfect Fit™ systems, use a fixed-displacement (Sanden style) compressor. Even experienced auto AC installers sometimes forget that the procedures for charging a fixed-displacement compressor system are different from those for the variable-displacement compressor systems used on modern OEM vehicles.
The procedures are different because many charging stations charge the system with the refrigerant in a fluid state and a fixed-displacement compressor is not designed to pump fluid. Therefore, you must not charge the system with the car running (as that would cause the compressor to pump fluid. Also after you have charged the system but before starting the car, you must hand turn the compressor (to get the fluid out). Be sure to point these differences out to your licensed AC professional if he works mostly on modern vehicles. (Note, although some charging stations do not charge the system with the refrigerant in a fluid state, we believe it’s simpler and safer to follow these procedures in all cases.)
1. Make Sure the Compressor Belt is Properly Adjusted
Serpentine belt systems typically have a spring tensioner and will adjust themselves appropriately. With a V-belt, we recommend starting with an inch of play. If it is not tight enough, it will squeal on the pulley. The general rule of thumb is tighten it until it stops squealing but no further. If you can’t tighten it further and it is still squealing, you probably need a shorter V-belt. (Note, over tightening will cause premature system damage as well.)
2. Check the Direction of the Water Valve
Classic Auto Air water valves come with labels to indicate proper connection to heater core and pump.
3. Check the Orientation of the Compressor
The compressor should not be rotated more than 90 degrees off the centerline of the oil fill plug. Keeping the oil plug on the top of the compressor ensures that oil does not drain out the compressor hoses when the compressor stops running. (If the oil did drain out, the compressor could seize upon system start up in the same way an engine without oil would).
4. Evacuate the System for 30-45 Minutes Before Charging
The AC system needs to be evacuated to remove air and moisture and check for leaks. If everything is in order, the low side should reach a minimum of 28-30” Hg within a short period. After 30-45 minutes of evacuation close the service valves and turn off the pump. Let the system sit for 10 minutes. If there is vacuum loss of 2” or greater, there is probably a leak. If there is a leak, the first place to check is the O-rings as it is not unusual for one to have been crushed or split by over-tightening during installation.
Evacuation Note:
We’ve been surprised at how many people underestimate the importance of evacuation, thinking it’s only to check for leaks. It is also necessary to remove moisture from the system. Moisture in the air conditioning system will cause corrosion due to acid buildup and premature component failure!
5. Compressor Oil
Ask your compressor supplier whether the compressor already contains the appropriate amount of compressor oil. New 134a compressors from Classic Auto Air come with the appropriate amount of PAG oil, so if we’re your compressor source, you SHOULD NOT add any more compressor oil. Excess oil will disrupt the proper operation of the refrigerant and cause inconsistent cooling and at some level will cause the compressor, which is not designed to pump fluid, to fail.
6. Do Not Charge the System with the Car Running
Modern OEM variable-displacement compressors are often charged with the car running. Fixed-displacement (Sanden-style) compressors should never be charged while the engine is running. Doing so will damage the compressor and void the warranty. Many charging stations charge with liquid refrigerant and if the car is running the liquid refrigerant will be pumped through the compressor. Pumping liquid refrigerant through a fixed-displacement compressor will damage the reed valves and pistons. You’ll know this has happened if the compressor taps or ticks while operating.
7. Add 134a Refrigerant
Our systems require 1.5lbs (24oz). Do not add more than that. ADDING MORE REFRIGERANT WILL NOT LEAD TO COOLER TEMPS. Our systems are designed for 134a refrigerant. Use of any other refrigerant will damage the system and void the warranty. If you are not using a Classic Auto Air system, ask your system supplier how much refrigerant to add.
8. Hand Turn the Compressor 15-20 Revolutions After Charging
This is another instance where fixed-displacement (Sanden style) compressors are different from variable-displacement compressors. You should point out this difference to your licensed AC professional if he typically deals with modern vehicles. If you have charged your car from a charging station, there will be refrigerant fluid in the compressor. Before initially turning on a fixed-displacement compressor, you must hand turn the compressor hub (the clutch-pulley assembly, not just the pulley) 15-20 revolutions to get the refrigerant fluid out of the compressor. Failure to do this will damage the reed valves and pistons. Again, you’ll know this has happened if the compressor taps or ticks while operating.
Please contact us if you would like our New A/C System Charging Procedure & Checklist Booklet. Finally, remember, auto AC systems should only be evacuated and charged by a licensed professional.
