I’ve been playing around with this problem for a month now. I THINK I have it figured out, but would love some input from you guys.

Background: I have 1977 300D with 128K on the clock. I’ve had it for about 3 years now. A little over a year ago I removed the old York AC compressor and replaced it with a new 7 cylinder Sanden compressor. Since I had a decent supply of R12, I kept the system running on R12. About 6 months ago I replaced the “Evil-Servo” with one of the modern controllers from Unwired Tools (https://unwiredtools.com/accii.asp). All has been well until the system would randomly start blowing warm air. At first I assumed I had a leak and had lost my R12. But the gauges said otherwise.

So my situation was that the AC clutch would engage, but the compressor would not pump. I immediately assume the compressor was bad. But it was brand new! I was pretty confused. So while driving the car around running some errands, I turned the system on and the AC was icy cold in seconds! It worked perfectly for a couple of days. Then it stopped cooling again. I put the gauges on it and with the compressor clutch engaged the pressures were equal. It was exactly as if the compressor was not turning, but it was. So, later that day while still pretty confused, the system started cooling again. I put the gauges on as soon as I got home and the numbers were good. Plus you could see a bubble or two pass by the drier’s viewing port. It was working as it should.

So I searched high and low on the Internet and had no success in finding a problem that matched mine. I spoke to every AC tech I could find and got a lot of suggestions/comments. Some potential problems I read about on the net were ruled out. For instance, the first thing I thought was that the expansion valve had failed in a totally open position. But techs and most Internet folks said that even if the valve failed while fully open there would still be a significant difference in the high side and low side pressures.

The Sanden compressor is a 7 cylinder wobble plate machine that uses reed valves to open and close to facilitate compression.




So, the question is; what are chances that the reed valve assembly would fail in such a manner that it worked sometimes and not others? Is it feasible that foreign matter moving around that occasionally block one or more reed valves open causing the compressor to not generate discharge pressure? Since I don’t really know the full history of this car, is it possible that someone converted it to R134A without changing the service ports and I now have a nasty mixture of PAG and Mineral Oil? Any other ideas??

My game plan right now is to order the gaskets and the valve plate before opening the system up. I will then open the compressor (after having local shop reclaim/recapture the refrigerant) and see what it looks like in there. I will replace the valve plate and button up the compressor with new gaskets. I will then flush the system, replace the drier & expansion valve, add oil to compressor, drier & evaporator, evacuate the system, pressure up with Argon (because that’s what I have on my welder) to check for leaks. I will then evacuate again and recharge.

Am I missing something? Am I totally wrong on the diagnosis?

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Baton Rouge, LA
1977 300D Non-Turbo

I'm not an expert on the internals of these, but is it possible that the clutch was slipping intermittently?

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'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild

So when you changed from the York to the Sanden you did not flush the system ?

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Clutch isn't slipping. Sure wish if was!


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Baton Rouge, LA
1977 300D Non-Turbo

Nope.

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Baton Rouge, LA
1977 300D Non-Turbo

Review the youtubes on refreshing similar compressors and you won't feel afraid to tackle it. Fairly simple and obvious inside. Just replacing seals isn't worth it to me since the kits cost ~$40 and I have bought new Sandens for that on ebay.

I had a similar experience with the compressor on my 2002 T&C 3.8L. I forgot if Sanden or Sanyo, but similar swashplate design w/ ~7 double-acting pistons. The rebuilt compressor made a slight rattling noise from the get-go, but finished one summer with it. It got much worse by May of the next year, so I removed and opened it. I found the rebuilders had assembled it wrong (big place in Jackson, TN). There were 2 flapper plates (lower left of photo) on one side and none on the other other side. It only worked somewhat because the backer plate (lower middle) was acting as a flapper (i.e. check valve). I wasn't confused, the backer on that side had marks from impacting the ports. I re-assembled correctly. Indeed, I used the center section (piston/cylinders/swashplate) from my original compressor because it had much less play. Still working fine ~4 yrs later. It would be hard to re-assemble incorrectly since some plates were labelled "F" and "R" and the others fit the alignment pins only one way, but those gomers managed to. That compressor had just metal seals on the end caps, but I recall Sandens use a face O-ring (swapped a rear cap once to get GM Pad ports for my M-B).

The main tricks are an impact ratchet helps remove the clutch nut (shaft doesn't spin), pry off the clutch face then look for a snap-ring which secures the pulley. I didn't see that when disassembling my failed compressor for forensics and tried prying off the pulley, which damaged the snap-ring groove. I found my original compressor was actually fine and the clutch must have slipped from over-pressure on a 108F day, melting it (sprayed molten plastic out). Since a clutch cost about the same as a compressor w/ clutch, I bought the later, but clutch alone would have been a simpler on-car job (don't touch refrigerant). I run Duracool in all my vehicles now, so lower pressures.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans