My electric fan on my '94 940 has begun to stay on for quite a long time after the engine is off, long enough so that the battery becomes drained to the point where it wont start the car. It does turn off, just after a while. My questions are, what is sending a signal to the fan relay telling the fan to turn on or off? Could the culprit be the relay? Any insight would be appreciated.
With Bosch injection, the computer turns the fan on and off. With Regina injection, there's a temperature switch in the right radiator tank. Also you have a trio of pressure switches in the lower front right corner of the condenser - these are involved in turning the fan on as well.
Thanks. My car is Bosch injected. Can some someone tell me where the temp sensor for the fan is? I'm assuming theres one pluged into the coolant system somewhere. OR does the computer use the ECT sensor or temp gauge sensor for this? (both of which I've recently replaced) I've found and pulled the cooling fan relay, the relay in front of the battery, and I'd like to test it. Anyone know how to test it? Thanks again.
It is Bosch injection. I've found the relay for the cooling fan, in front of the battery. Is there a way to test if the relay sticks? Also, does the computer use the Temp Gauge Sensor or the ECT (engine coolant temp) sensor to determine when the fan turns on or off? Thanks again.
Since the fan is on half speed the ground signal is on the BL/SB wire going to terminal 1B on the fan control relay it comes from either the low speed fan pressure switch in the condensor or the climate control head in LH cars or the thermostatic switch in the radiator for Regina cars. Bottom line? The controller is bad.
Grounding the W-SB wire with your test light should engage high speed. That signal comes from the high pressure switch in the condensor, all cars.
Bob
Thanks Bob. I'll look into replacing the pressure switch in the condenser. Can someone please explain to me why these switches in the condenser, signal the electric cooling fan to operate? Does something about the condenser and A/C system coincide with the engine temp? I dont get it. Thanks.
If the pressure in the condensor is low then the signal ground from the condensor switch agrees with the ground from the climate control head inside that also gets a temp signal from the ECU if it's an LH car. If it is a Regina car either the a/c low pressure or the radiator temp "otter" switch supplies the ground signal to the relay.
If the a/c condensor pressure goes high then the fan runs at full speed to help lower the head pressure on the compressor by allowing better condensation in the system. Also since more heat is being release upstream of the airflow into the radiator moving more air through the "sandwich" keeps everything cooler.
All you have to do is unplug the switches and see if the fan stops running. If not then the relay is toast, which is usually the case.
Bob
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