kkswow12

maybe this should be in the silly Q threads, but maybe not, when i turn on the key, in the on position there is, i am assuming...i know i know, that it is the blower fan that comes on in the just barely on setting...i have turned off all the switches i can find and it doesn't go off...doesn't seem right to me, anyone familiar with this? it is a 91 C2 manual, thanks ahead, kevin

crg53

If you are talking about the 2 blowers in the dash, Yes they are always on as soon as the power is turned on with the key.

wilson234

I noticed the same thing, wondering if this is normal? It's the blower in the engine compartment.

crg53

When you turn the key to the "on" position, the DME runs through a check cycle, which amongst other things include running the engine compartment blower for a few seconds, and cycling the resonance flap. The A/C fans in the dash are always running with the key one or when the engine is running.
The engine compartment fan should only run when you turn on the heat on the CCU, other than what I mentioned above. It will also run when you shot down an extremely hot engine, that way blowing air through the HE, to help cool down the engine, but will shot down when desired engine temp is reached.

ToreB

crg53, you are not entirely correct.
The rear (AUX) fan is controlled by the Climate Control Module, and there's no startup sequence or similar for the rear fan operation. The rear fan has two purposes. One is to help blowing air through the heat exchangers onward to the front fans to improve the heating of the cabin.
The second function of the rear fan is to do additional cooling of the heat exchangers/engine when in normal operation, (if temperature **** is set to minimum and mixer servo flaps are closed) and at ignition off by blowing the heated air out through two spring loaded dump valves under the engine.
The CCU supervises the engine/air duct temperature with a temperature sensor, and run the fan at low speed (40-45degC) and high speed (62-57degC) when ignition is ON and mixer valves are closed. (minimum heat setting) At igntion OFF, the fan run in low speed if the air duct temperature is above 75degC, and shall stop when below 70degC.
If the rear fan runs for longer than the CCU shutdown time,(up to 20 minutes) you may have a problem with the rear fan relay or the internal CCU shutdown circuit. All details on this topic can be found here.

Cheers,
Tore

crg53

Tore, I am not questioning your knowledge, you are way ahead of me when it comes to electronics, but I will bet you dime to $ that my fan used to start up momentarily when I first turned on the ignition. Haven't had the fan in there for years now, but do remember the sequel the old fan made, before I replaced it with a new motor.

ToreB

crg53, thank you for your information. There are several versions of the CCU out there, all behaving slightly differently. The main point here is the thread starters, the rear fan shall not run unless it is hot enough back there, or if you need heated air to the cabin. (depending on CCU temp setting and ambient temperatures)
It is also very common to see failed rear fan low speed resistors, and this causes the CCU to switch to high speed. I also see a lot of damaged rear fan relays, either sticking or failing to turn on the fan in either speed.
Cheers,
Tore