I need help charging my A/C

August 1, 2012 | By Richard Prince


I have a 1988 Airstream 325 motor home on a Chevrolet P30 chassis with a 454 engine in front of a TH400 transmission. I want to charge the air conditioning with a product known as Freeze 12. I have the Freeze 12, but I don’t know how much to put in the system and I don’t know how much oil to put in. There are no labels anywhere on the vehicle to tell me how much of each I need. I know that too much or too little refrigerant or oil will not make for a cold-running system.

The system has been flushed, a new compressor was installed, a new expansion valve, new hoses, and a new receiver/dryer were installed, and the condenser was removed and checked for leaks. I have put a vacuum pump on the system and it will hold a vacuum.

I have a set of manifold gauges. I could get my hands on R12, but I would rather use the Freeze 12 because it is readily available and cheaper than R12.

The system in the vehicle was not installed at the Chevrolet factory, it was installed by Airstream.

No one at Airstream can give me an amount to use because they don’t keep records on the systems installed in those vehicles at that time.

I have been told of many different amounts to use, but obviously there is only one right amount.


You’re correct when you say that there is only one right amount of compressor oil and refrigerant but unfortunately I can’t tell you what that one right amount is as my research yielded no concrete answers. And even if you found a spec for the original refrigerant it would not necessarily be accurate for the Freeze 12 substitute you’re planning to use.

It doesn’t help you any, but a good rule of thumb for anyone servicing or rebuilding an air conditioning system is to keep careful track of how much oil came out of the system when you drained all of it. Absent a significant leak the amount that came out is usually pretty close to the amount that should go back in.

All I can think of for your situation is to bring the motor home to a very experienced air conditioning shop that may have some understanding of what your system requirements are.