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Old 07-05-2019, 11:11 PM
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Join Date: Nov 2018
Location: Dallas, TX
Posts: 48
82 500SEL low speed aux fan


I have a problem with 1982 500SEL euro.

I replaced the inline pre-resistor for aux fan, however, jumping high temperature switch pigtails does nothing to aux fan. If you remove the relay and jump pins, fan comes on. Both relay sockets get voltage.
I tested the relay by swapping it with the high speed one and it is good. So the issue is with wiring?
Pigtails tested show 0V.
Does anyone have a wiring diagram so that I can ensure proper wiring from the pigtails to the fusebox?

Thank you!

Update: Found wiring diagram in German. Seems that the issue is in wire from receiver drier to fusebox relay C or one of the brown wires at receiver drier has a bad ground. Will investigate further.

Last edited by filp; 07-07-2019 at 02:34 PM.
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Old 07-10-2019, 02:30 PM
Registered User
Join Date: Nov 2018
Location: Dallas, TX
Posts: 48
Ground wire was bad.
Fan works when both pigtails are jumped. Without jumping, only 100C coolant temp switch turns on the fan on high.
Therefore we can argue the high temperature switch on receiver/drier is bad.

Now the interesting part: the service manual claims it can be removed without evacuating the refrigerant.
New one comes with a rubber o-ring and seems to be a pressure switch...
Who's right?

The manual seems to talk about this: https://www.*******.com/products/mercedes-porsche-a-c-refrigerant-temperature-sensor-meyle-0008208010

While suppliers mainly sell the later "red" switch. I have to check which one is on the car.
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