GM & Aftermarket A/C Compressors vs MB compressors
 

Some time ago, the following was posted on alt.auto.mercedes. Can anyone confirm or provide a link to a manufacturer's site that confirms the difference in lube oilhole between GM and MB compressors?

"A word of advice on buying a replacement compressor:
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, a month,
6 months.... depends on the quality of the bearing they put in. "

Here is link to Google Groups:

http://groups.google.ca/group/alt.auto.mercedes/browse_thread/thread/8db733da96f6ae79/6f27b1d537b97996?q=mercedes+air+compressor+oil+upside+down&rnum=4&hl=en#6f27b1d537b97996

Bull *~!?

I have installed at least 50 R4's that didn't come from MB on MB's & never have seen a premature failure!

Here is a good example of that MB crap! The A6 compressor from a MB dealer lists for $2,370!!!! I buy that exact compressor from a GM Delco supplier brand new for $305!! & that includes the clutch. Does MB really need to make $2,000 profit on a single compressor?????

Whoever wrote that probably meant mounted low or mounted high.

Questions still comes down to whether or not the compressor end caps are rotated on MB,s for proper lubrication.

This story keeps coming up on the net and I am just trying to get a definitive answer.

The GM A6 has a "sump" and must be mounted sump down, the R4 doesn't have a sump!

I just took the yoke off the front of a GM AC Delco R-4 that I had sitting around. It was NOS for a 90's Chevy Suburban (I think....pretty sure).

Despite what I thought :shocked3: (and what some have said on some of the other MB mailing lists and forums), there WAS an "X" and TWO oil journals on the inside; one to the front needle bearing and one to the shaft seal.

The journals point to the center (obviously), so mounting this R-4 with the "X" up would seem to be wise; gravity being what it is and all.

I have taken apart several other R-4's and never noticed this before. The yoke on this R-4 was the smaller version (there are two models of R-4's; lightweight and regular).

Thanks for checking this jbaj007 - First report that the "X" is actually there and that it can make a difference!

Compressor comments...
 

Hi there,
For what it's worth, the A4 compressor on my Astrovan is mounted on "top" of the engine. It's actually mounted on the accessory mounting plate, which bolts to the front of the heads and block, but is above the block itself. I believe the one on my S15 pickup is the same. Interesting advice, probably a good thing to keep in mind. An AC guy I trust says to use Sankyo compressors as they last longer than the A4 compressors. I don't know from personal experience, though... the A4 compressors on my rigs all work ok, just are noisy in hot weather.

Regards,
Richard Wooldridge

Now I'm confused. :confused: I have heard the same story about not using an R-4 designed for a GM product for the reason pointed out. MB Doc, you stated that you have installed at least 50 R-4s that did not come from MB, but you were not clear as to if these compressors came from aftermarket sources but were still intended to be installed on MBs and not GMs. Please clarify.

Thanks,
Peter

It's true!
 

Hello all,
I just checked in the factory manual for my 1985 S15 pickup truck, and in the R4 overhaul section it does rather clearly state in the R-4 compressor front head and/or O-ring section page 1D1-18, (REPLACE, Par 3) "Position the oil hole in the Front Head to be "UP" when assembled to the compressor cylinder to correspond with the "UP" position of the compressor. Install the Front Head and tighten the front head mounting screws to 27 N'm (20 lb. ft.) torque."
There is also a picture that shows the oil hole. The front bearing is a needle bearing, and the front head is held on with 4 screws. Seems to me that it would be a simple thing to rotate the front head to the desired position before installing the compressor, it might be a good idea to use a new o-ring. The only problem is that one would have to pull the clutch and clutch coil off the front head to get to the screws.
So here's the dilemma- the oil hole really doesn't have any oil collection surface, so does it really matter if it's up or down? If it's down, the oil will enter the bearing area along the shaft surface and leave from the hole, if it's up the oil will enter through the hole and exit from the shaft surface. There's not really that much difference in my opinion. But, it appears the information given is correct.
Regards,
Richard Wooldridge

You get the idea, even with quicky photos.

well cadelac put the compressor on top of the eng. in the 70"s in front of the carb. even the log fregadair unit,was on top.also oldsmobile.

Well today my comperssor siezed so I will be removing it and installing the old one I had. The new (not rebuilt) one was from ACKITS.com It has lasted 1.5 years. The old one was installed by Mercedes at ******** in the DFW area. I will compare the 2 and let you know.

Dave

Dave

What did you find?

I just had a new R4 fail during charging and somebody reminded me of this thread.

Failure during charging is usually:

1) Just a bad compressor sneaked thru QC.

2) slugged by charging refrigerant as a liquid and the reed valves popped.

3) debris from previous compressor failure hit the new one.

What about substituting the R-4 with a Sanden, Sankyo or Denso etc compressor . Any suitable models of these for my 300SD (compressor locked up ) ? - Thanks