I purchased a rebulit R-4 A/C compressor for my 79 300SD, and I need to how many ounces of compressor oil needs to go into the compressor. It say 10.0 which I am thinking that it is 10 ounces. Does this sound right? This is the first I have replace the any A/C compressor. Your input would be very helpful. Thank you!



Candy Verbeck

Hi there,

My book is fairly vague about the amount of oil for the compressor. I think the entire system takes 12 oz. The compressor takes 6 oz, but 3 oz will accumulate in the evaporator, and another 1 oz will accumulate in the condensor, and another 2 oz will be retained by the accumulator. So, if you are replacing the compressor in a system that has not had any oil leakage, you should put 6 oz of 525 viscosity oil in the compressor. It won't hurt to put an extra oz in just to be safe.

THE IMPORTANT THING IS TO USE 525 VISCOSITY OIL!!

Otherwise the compressor life will be quite short. When folks perform an R12 to R134 conversion and have compressor failure right away, its usually because they used the oil that came with the conversion kit, which is only 150 viscosity oil. You have to purchase the correct oil for the compressor!! Ester oil is available in 525 viscosity, but is not included with the little kits they sell because most compressors will work with the 150 viscosity oil. Unfortunately, R4 compressors will fail with 150 viscosity oil! Hope this helps!

Richard Wooldridge
'82 300D/4.3L V6

Thank you very much for your input. The instructions that came with the compressor said about using a mineral oil for the R-12. Would the mineral oil affect the life span of the compressor than the oil that you suggested?Would it make the life span shorter or longer? It is a refrigerant( not sure if this is spelled correctly) mineral oil.

Go to aircondition.com. There is a helpful area there that gives this information for each type compressor.

If you are staying with R12, the standard mineral refrigerant oil is the right stuff.

Good luck,

Larry is right. If you're staying with R-12, a CFC bases refrigerant, then the only correct oil type is mineral. If you're doing a R-12 to R-134A conversion, then there are two options. Either a POE or a PAG type oil is compatable with the HFC based refrigerant of R-134A.

The important point is if you convert to R-134A and continue to use the mineral oil you will have problems. The mineral oil reacts to the HFC based R-134A and creats a gel type substance. This gel will, at the minimum, coat the inside walls of your evap coil reducing heat transfer. But most cases it gums up so bad it clogges the expansion valve.

Jeff

Hi again,
Larry and Jeff are quite correct in that if you are using R-12 refrigerant, you must stick with the mineral oil, 525 viscosity. It is a special refrigerant oil, as you thought, and is available at any refrigerant supplier. Since you are replacing the compressor, I made the (incorrect?) assumption that it had failed from an R134 conversion, as they will all do, if the correct oil isn't used. Sorry about that! If you do switch to R-134, the system should be flushed as completely as possible, and the correct oil used as mentioned in my earlier post, to prevent premature compressor failure.

Richard Wooldridge

One last thing -
The 10.0 refers to the fact that it is a 10 cubic inch compressor.

Richard Wooldridge

Thank you very much for all you help and advice. Thanks again!