I recently purchased a 1985 300d. The A/C belt was missing and the RPM gauge wasnt working. I researched that the A/C will not work unless the RPM gauge is working because the RPM gauge sends a signal to the Klima Relay. Well I fixed the RPM gauge by using a jump wire in the EGR control module. Now that my RPM gauge works I then installed the A/C belt. When the engine is running, I then turn the temperature knob to the farthest blue setting (Cold) and turn on the fan and switch the air vent positions. The A/C compressor isn't activating and the electric fan in front of the A/C Condenser isn't turning on??? What can be the problem???

Can someone help me by telling me the order in checking things and how to check those items, such as how to test the Klima Relay with a Voltmeter and/or the compressor for example???

Thanks!

Is the system charged? Can you turn the "inner" portion of the a/c compressor clutch?

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Jim

Well, looks like I need a new compressor because this one is seized. I jumped terminal 5 and 7 in the Klima relay and engaged the compressor only for the engine to die every time. So I will replace the dryer, condenser , and the hoses because they are all old, better start new again.
I have read of the multiple problems with the R4 compressor, with the number one issue being the front seal leaking which causes the failure. I have read that the Sanden compressor should be used but you will need an adapter. I have researched on the adapters and I have narrowed it down to 2 company's. "Company A" kit has a custom welded bracket that you bolt on in place of the stock MB bracket piece that is bolted onto the engine block. "Company B" kit has bracket pieces that bolt onto the Sanden compressor then it is bolted to the stock MB bracket that is bolted to the engine block...also, this Company B states that the first company with the welded bracket has had issues where their welded bracket from it cracking due to stress and makes it a point on why Company B kit is better.

1) What has everyone done here?
2) Replace the R4 compressor with another R4 compressor?
3) Use a Sanden compressor but what kit should i use?
4) Is there a compressor other than the R4 compressor that is a direct bolt on replacement?
5) Would the GM A6 compressor directly bolt on???
Thanks!!!

i think one of the forum members sells a bracket for the sanden?

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1981 NA 300D 310k miles

The R4 compressor is fine as long as it has enough oil and is running R12. Save your money on the hoses, they're designed to last a lifetime.

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'83 300D, 126K miles.

So, if I get a new R4, what brand should I use? I definitely want one with a lifetime warranty. Should I replace the condenser also??? I was just going to replace the dryer. Also, what oil should I use with the R4? Does the BG products Frigi-quiet work well with the R4?

Thanks!

I am using the newer PAO 68 oil in all my cars. It works w/ all refrigerants and past oils, doesn't absorb moisture like PAG and is more efficient (less coating of condenser & evaporator tubes). Duracool calls it "Oil Chill" or such.