My electric fan is stuck on high..it runs as long as the car is running. Anyone ever have this problem? Any ideas?
TIA Charles

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1987 300D

My guess-This is only a guess-Is high resistance in the ECT (coolant temp sensor). Try jumping the 2 wires for the fan relay at the temp sensor, that will disable the fan temporarily until you can replace the temp sensor. Could be just loose or corroded sockets at the sensor as well, so check that out. If it ends up being the sensor, if you leave the jumper wire connected temporarily, remember to pull the jumper off to run the fans if the engine temp starts to rise too much.....Gilly

I would also check resistor R-15. It's the big white one next to the AC drier (behind driver's headlamp). Check the resistance. If it is burned your fans will work full speed instead of half speed.

Vinamg

Vin: But I don't believe this would make the fans come on whenever the ignition is on. I would first suspect the engine temp sensor, then maybe the freon high pressure switch (don't think I've seen one stuck open like this, though) or possibly the high speed fan relay itself. Temp sensor is more common, but you never know if a guy has "the common problem" until it is tested.....Gilly

If you are having this problem even when the engine is cold then most likely you have a faulty temp sensor (like gillybenz stated). However, if your problem is only once you reach working temperature then you probably have a faulty resistor (which would make fans work at high speed only).
BTW if the coolant sensor is faulty I wouldn't leave the wires bridged. Especially if it's very hot in your area and if you operate AC. Your car will definitely overheat. If it's pretty cool outside you could probably leave it and monitor temp like gillybenz explained.

Gilly: I've never seen a high press switch stuck on closed loop either. BTW I think the high-pressure switch on these cars only operate half speed using resistor R-15. I've bridged a few in the past as a temporary fix due to a faulty switch.

Vinamg



[Edited by vinamg on 04-18-2001 at 09:58 AM]

Vin: Now that I think about it, if he jumps the higher temp sockets on the temp sensor, and the fan goes into low speed, it's pretty well diagnosed right there. If he can also jump over to the low temp socket and the fan shuts off, that pretty much completes the diagnosis as far as I'm concerned. Only other thing he could do is verify his findings by getting out the book and checking resistances through the temp sensor pins. On the resistor block, I think these are 2 seperate paths, if the resistor goes out, it will prevent the low speed to work. i believe on this car there is only the one to run the fan at low speed, the high speed fan has no resistor block......Gilly

I totally agree.

Vinamg

Better stuck ON than OFF!!! My 92 400e needs a new engine wiring harness. The insulation on the wires at the temp sensor is deteriorated, causing the sensor to bridge and killing the fans completely.

Guess I should of taken care of this before buying rims, huh!

Peter

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Peter Balias
pbalias@hotmail.com
1992 400E
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