A friend and I are replacing the a/c compressor in my 1981 Imperial and the instructions say "only the correct amount of PAG lubricant is acceptable". However, it does not say what the correct amount is. We think it is 3 ounces - any input would be greatly appreciated.

No one can help with this questions? Perhaps I asked it the wrong way. The R134 compressor was shipped dry, how much lubricant do we need to put in? Thanks again.

You might try over here. They have helped me before.

A/C forum

In 81 that should be an R12 system. Most R12 systems used mineral oil and it is my understanding that PAG and Mineral oil don't like each other. For that reason I use Ester Oil since it is compatable with both PAG and Mineral oil systems.

What type of compressor is it?

It has already been converted to R134. Thanks.

When you converted it did you flush all the old mineral oil out? There is oil in everything because the Freon would carry it along. R134a won't carry mineral oil so they used PAG or ester oil since the R134a would carry it to lubricate the parts.

Most R134a conversions simply add R134a and ester oil to the system and the mineral oil finds a low place to make a new home for itself and just sits there. If you put PAG oil in a system that has not been purged of mineral oil it will react with it and clog everything up. (I never did it but have heard many 3rd party stories).

If your not 100% sure the mineral oil is cleaned out of the system use ester oil.

Thanks for your response, but the car was converted a long tima ago- several years. Do you still think that PAG will be a problem? Also, how much oil do we use?

The Mineral oil will be there until you completely flush the system. There will be several ounces hiding in the evaporator, condensor, drier and any place that has a low spot for it to pool.

There are other oils out there now if you don't like ester but I would not try the PAG if it were me. The cleanup of a gummed up system is a nightmare on some cars.

I bought a 1/2 gallon of ester at NAPA and never looked back. I use it as needed in any car.

What is the make and model number of the compressor? Did it ever operate correctly? What is the reason the compressor is being replaced? Leaking, noisy, no-pump, torn-up, other? If leaking, how long has the system been empty? We need to klnow some of these things before determining oil charge.
Ron