On the 85 300 D I have here is where I am at:

When I turn on the A/C at the climate control I have NO power at the 2 wires that go to the low pressure switch on the drier.

I have verified that my push button climate control unit is good. I swapped mine to another 85 that has working air and it works on his car.

I also swapped my Klima relay on the same car and it is good also.

I checked the micro cutout switch and it is not stuck or showing contact via multimeter when not pressed.

I disconnected the temp sensor in the head and it has not effect on the A/C.

Independent power to the compressor clutch activates it just fine.

What am I missing????

When the climate control unit calls for A/C is there some other relay or switch that it must pass through before it gets to the low pressure switch??

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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

Do you have power at the evaporator temp regulator?? located next to the expansion under the passenger under-dash panel.

The pushbutton sends power to the ETR & from there it goes to the low-pressure switch.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Oh...I am not sure, I did not even know to check that!

I will look for it. You say its next to the expansion valve?

__________________
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

Diesel Giant,

Have you shorted the the connector pins at the low pressure switch located on the filter drier. Don't do it with the engine running. Do it with the key on, engine off and listen for the compressor clutch clicking.

Best of luck,

I have the same issue on my W201. One day it just stopped working. I have no power at the switch at the Dryer! So shorting the two out no longer engages the compressor. Funny part it that is will work for a few seconds then does not until the next restart of the car. I have no idea of where to look now since there is so much that can affect it. I had high pressure according to a cheapo gauge on the low side line. Someone on another forum said it was blockage. I drained the system and then re-filled. But after a little bit it goes to high again, stays at normal for a few minutes then bam high pressure. I was thinking the expansion valve was shot, but would like some more info. So I am keeping my eye on this thread in hopes that I could have a similar problem. Was fine then all of a sudden one day it just stopped.

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....

Jamie,

Yours is a different situation than Diesel Giants. Since it is kicking in for a second or two, yours has a slipping belt for whatever reason. There is a sensor on the compressor that can tell if the belt slips. If it detects slippage it shuts it down until engine is started again.

Turn the compressor by hand and ensure that it is free. If it is free then start checking your belt for oil or your belt tension for looseness.

Good luck,