Any one you get that does NOT come from Mercedes will have the front bearing cover installed UPSIDE DOWN. Look at the cover on the front behind the clutch. It will have 4 bolts. Between 2 of the bolts will be an embossed X. This is the position of the oil hole to lube the front bearing. The R4 compressor was originally designed for GM cars with the compressor mounted on top of the engine. The X and the inlet/outlet port is UP. Mercedes used the compressor but rotated it 180 degrees and mounted it under the engine. This put the ports DOWN. Then they rotated the front cover so the X is UP. Oil does NOT flow uphill. If you use an aftermarket compressor with the X down, you will starve the front bearing of oil. It may last a week, amonth, 6 months.... depends on the quality of the bearing they put in. "I have received feedback on that information confirming that it is basically correct. That DOES NOT Mean that if you mount an R-4 upside down, it will fail prematurely - only that it is much more likely to fail prematurely if you mount it upside down. I have had many people dispute this and tell me that, "I mounted my compressor without an X on it and it's still working 10-15 years later. No argument, but there really is a reason why Mercedes marked their compressors and most of the guys I've spoken with that do this for a living (and don't want comebacks) insure that they use compressors configured to work on a Mercedes. Marshall--Marshall Booth Ph.D.Ass't Prof. (ret.)Univ of Pittsburgh School of Medicine

-- Jim

Thank you Herr Cathey!

This is the post that I remember. I have never had to buy a new GM compressor, so I don't know firsthand. However, Herr Doktor is about the most reliable source as there is.


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