Ok I am still fighting this horrible problem. On the 85 300 D. I have no power at the low pressure switch. On my searching of the archives, I understand the ACC sends a signal to the Klima, then to the low pressure switch. I am not getting power to the switch. Voltmeter shows no voltage even if I jump the Klima to get power to the compressor.

I hate electricity. I would rather rebuild an automatic tranny.

Can anybody help??

Short of throwing parts at the problem, I dont have many other options left. The Acc seems to do everything right, except turn the compressor on. Or maybe the Klima is bad or both. I wish someone nearby had an 85 that I could swap parts to see if they are bad. My 79 uses a different climate system.

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

There is a diesel forum here. You're likely to get more answers on it vs. the gas forum you've posted on.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

This is the "tech" forum. All manner of questions are asked here whether compressions ignition or "gasp" petrol.

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

I'm not very famliar with the diesels. However, my brother who has an 84 300D Turbo had a similar problem and found that the pneumatic relay which controls the compressor boost was plugged up with soot. He cleaned it and the problem was solved.

Problem was the evaporator temp sensor.

__________________
1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair