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Old 05-06-2003, 03:21 PM
MS Fowler's Avatar
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Join Date: Jan 2003
Location: Littlestown PA ( 6 miles south of Gettysburg)
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R4 Air conditioning compressor questions

I have a W123 chassis with dead air Conditioning. Based on reading many posts on this topic, I plan to keep the system R12.
As a first step I will replace the compressor. I pulled the old R4 compressor off last night and noticed that it had a "Notice" to the effect that mounting bolt holes were metric. So now I have a question--Are there different models of R4 compressor? I had hoped they were all alike and I could find as late a GM car that used the R4 and pull the compressor. Is that still a vialble plan, or are there different R4s. If there are different R4 compressors, which will work on my W123 (240D)?
One more question--How can I tell visually which is a good compressor--IS there a std failure mode ( like the front seal on the older A6 which left an oil streak on the bottom of the hood)?
What do I look for?
I will also get a new reciever/dryer, flush the lines, and apply vacuum for a long while.

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Old 05-06-2003, 03:48 PM
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Yes indeed, the one found on your car has a few threaded holes that are metric and there also are some later ones that use a different seal than the o-ring that yours had from the factory for the manifold connections.

I have "been there, done that" with rebuilt R4 compressors with terrible outcomes. I would suggest buying a NEW one especially for your car. Also after flushing I would highly recommend a suction side filter. This is an aftermarket inline filter that you can put into the low side line near the compressor inlet. It will prevent debris that was left behind after the failure of the previous compressor from spoiling your new one. Some people even go so far as to say that with a suction side filter it is not necessary to flush the system. I find this difficult to stay away from, the compressor is not the only part that can be damaged by circulating debris.

If you just flat can't afford a new R4, go to and post there for a recommendation of a reliable rebuilt supplier.

Good luck,
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Old 05-06-2003, 04:33 PM
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Join Date: Jun 2001
Location: Santa Monica, CA
Posts: 2,053
I've got to agree with Larry on the new R4, even though I'm currently "rebuilding" a spare one on my bench right now (more for my education than anything else). The original Harrison R4 has gone thru MANY incarnations with MANY manufacturers making genuine R4's over the years (SAE threads, metric, stepped ports, "O" ring ports, shaft nut, no shaft nut, etc. etc.) A new R4 is cheap enough that when all is said and done, for a "keeper" vehicle, it's not that big a deal for the peace of mind.

That said: a couple of listers here, and on the diesel mailing list, have used pre-owned ones from the wrecker"s yard. I think I'd only do that on a real utility-only vehicle.

Most common failure is the same as the A6 series (HR, HD, DA, etc.)....front shaft seal.

Whatever you do, DON"T ever use a chain store rebuilt R4 (Murray, Evercool, Four Seizens). It will DIE.

The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)
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