Cadillac Repair: Too much oil in new a/c compressor?, 134a freon, r 12 freon

Question
I just converted a 1991 cadillac to R134 when I installed a new compressor and drier.  It is cooling, but when the clutch engages, it seems to really slow the motor down, creating a rattling noise that seems to be coming from behind the transmission. I guess this is really two questions. The noise was noticed before I changed the compressor because of a noisy clutch. The low pressure reads 35 to 40 lbs, while the clutch is engaged, so I don't think I have too much 134. I added 3 oz of ester oil to the compressor, and about 2 oz.to the drier when I put everything back together.

Answer
When you replace a compressor you drain out the oil from the old compressor and measure how much you removed.

Next you empty out all the oil from the NEW compressor and throw away this NEW compressor oil and add FRESH NEW REFRIGERANT OIL from a NEW bottle of refrigerant oil into the new compressor in the EXACT amount that you removed from the old compressor.

You do the EXACT same thing with the drier.


When you convert from R-12 freon to R-134a freon you ONLY install, I believe 80% of the R134a freon into the system.

Therefore IF your system requires, 2.0 lbs of R-12 freon, Then you would ONLY add 1.6 lbs of R134a.

Check the sticker on the label usually near the drier to see how much R-12 freon the system holds and subtract 20%.

Therefore, IF the new compressor was filled with a full charge of approx 8 ounces of refrigerant oil and you installed it on the vehicle, You have way to much oil in the system. Howevr, If the new compressor had NO oil in it then your adding 3 ounces is correct and 2 ounces to the drier is also correct.

If your POSITIVE that you have the correct amount of oil in the system via the above method, Then it is most likely that you have to much freon in the system.

NOTE: Read the instructions on freon capacity on the retro-fit instructions.

NOTICE: You will most likely see the LOW REFRIGERANT message and or light illuminate on the dash telling you that you are LOW on freon.

WHY: Because the LOW PRESSURE SENSOR for the AC system is NOT calibrated to run on R134a freon. The ONLY solution to correcting this fault is to re-install R-12 freon back into the system as there is NO replacement low pressure switch available anywhere that is calibrated to run R134a freon on the 1985 thru 1993 year vehicles.

The manufacturer completly changed the AC system in the 1994 to current vehicles to run on the R134a freon.