I am hearing a noise that I think is coming from my compressor on my 85 300SD. Is there a way to check if the compressor has enough oil in it and if I did want to add some oil to it how would I do this? Do you put it in the low side and it will go thru the condensor + dryer to the compressor or can you add it somehow right into the compressor. About a yr. ago I had a mechanic put a used condensor and a new dryer on the vehicle and I do not think he put any extra oil in the system. And if I would try to add some oil about how many ounces would it take. The 1st thing I want to do is take the belt of the A.C. and see if the noise stops. Is there any other thing that could make the compressor noisey besides low oil?
















C.

Do you hear the noise when you don't run the AC? If it is the compressor you should only hear it when the clutch on the compressor is engaged (AC is ON).

The only real way to know how much oil is in the system is to take the refrigerant out, open the system, flush it, and put new oil in. If your mechanic put a condenser and dryer on the system last year, unless he doesn't know what he is doing or is not competent he more than likely put oil into the system before he charged it with refrigerant. I'm assuming you are using R134a?

You can add oil to the system either using an oil injector (via the low port) or getting one of those oil charge cans at any auto parts store. Doing this is really a crap shoot as you are not sure how much oil is in the system.

I would ask the mechanic that did the work as to how much oil and what kind he put in the system. Then you will have something to go off of. More than likely he put enough oil in and the compressor is just making noise which may or may not be a sign of future failure.

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

It is possible to get a rough idea as to the oil in an A/C system by opening the low pressure valve briefly while the system is running. I hold a small rod in my fingers, using it to depress the low pressure valve for a fraction of a second. The freon and any oil circulating will spray onto your fingers. The oil left on your fingers after the freon evaporates should be enough to lubricate them well.

A few years ago I converted two 25+ year old systems to 134a, and found not one drop of oil in the compressors or the dryers of either system. I guess it had leaked out over time. I added the recommended amount of oil with the 134a conversion and both systems worked well afterward. I decided to use the above method to check for detectable oil in the systems of the old vehicles I tend to drive. Apparently the exact number of ounces is not as critical as I had thought.

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'97 E 300 D

Thanks for the reply Nelbur. I really do not think the mechanic put any oil in the system when he changed the condensor and dryer this is why I am thinking the compressor is low on oil.I did run it with the air off and the noise seems a lot less but there is still some noise there. I will check some more maybe tomorrow and I might even try to loosen the belt on the compressor to eliminate the compressor and see if I still hear the noise. I did have to change an alternator a while back because that had noisy bearings and was thinking that maybe this one too is bad since it was only a rebuilt from A.Z. Thanks for the reply on feeling how much oil is in the 134 that seems like a good idea sure hope I do not have to replace the compressor as I know they are not cheap.