94 '940 colling fan not turning off

[roland]

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.

 

[Mike F]

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.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

[roland]

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.

 

[roland]

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.

 

[User]

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.

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

 

[roland]

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.

 

[User]

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