help with electric fans

[greythunder]

This is what I know...I think. The e fans come on "high" when the coolant temp exceeds 100°c. The come on "low" through the locomotive sized resistor, during some point of ac operation.

I had not seen them on at all during ac operation. I shorted the brown wires at the red thingie on the drier. Fans came on when ignition was turned to on position.

How do I troubleshoot "high" setting for excessive engine temps?

Does this mean the red thingie is bad?

I read to unhook the single wire coolant temp sensor on beside main fuel filter. I did that and nothing happened when ignition switched to on.

[Mxfrank]

It varies a bit by model, but here's the general idea:

1) The fan comes on low speed (through the resistor) when the a/c pressure is above a threshold level...300psi if I recall correctly. This is above normal operating pressure under moderate temperature conditions, so the fans may not always be on when the a/c is operating.

2) There is a fan switch, usually locate near the water outlet on top of the motor. It will turn the fan on at high speed when the temperature hits around 105. It may be a double element switch, which will turn the a/c off when engine temperature reaches 110.

[jay_bob]

What year/model of car do you have?

[greythunder]

92 300d 2.5. there is two "sensors" on top the motor where the upper rad hose connects. one has one wire, and the other has 2-3. I'm just trying to make sure all is well with these fans before the hot weather hits. just bought the car in jan.

[Mxfrank]

The fan switch is the one with three connections. On pole is the common ground. The other is the high fan switch. The final pole turns off the ac when you really overheat. High fan switch should connect to common ground when the temp is about 105. The other pole will also be connected to ground when the temp reaches 110.

[greythunder]

dude, you really know your *****. thanks for the info. is it safe to say, for test purposes, if i short the high to ground of the three, the fans should turn on?

[Mxfrank]

Yes. If you picture the three contacts as a "Y", the two you want to short are at the top of the Y.

[greythunder]

thanks Mxfrank. My 3 terminals are actually 2 separate sensors. one with 2 poles, and the other is a single. i shorted the sensor with 2 poles and nothing. then, shorted the harness (duh, it was early) and the fans fired right up. thanks for your help.

Maybe this should be a new topic, but do you know of a way to test the belt driven fan clutch? in comparison to my jeep cherokee, this one spins a lot more freely.

[Mxfrank]

Originally Posted by greythunder

thanks Mxfrank.
Maybe this should be a new topic, but do you know of a way to test the belt driven fan clutch? in comparison to my jeep cherokee, this one spins a lot more freely.

This time of year, no. If it gets hot enough, you should be able to hear it engage.