94 '940 colling fan not turning off

Discussion in 'Volvo 940' started by roland, May 1, 2006.

  1. roland

    roland Guest

    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.
     
    roland, May 1, 2006
    #1
  2. roland

    Mike F Guest

    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.)
     
    Mike F, May 1, 2006
    #2
  3. roland

    roland Guest

    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, May 1, 2006
    #3
  4. roland

    roland Guest

    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.
     
    roland, May 1, 2006
    #4
  5. roland

    User Guest

    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
     
    User, May 2, 2006
    #5
  6. roland

    roland Guest

    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.
     
    roland, May 3, 2006
    #6
  7. roland

    User Guest

    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
     
    User, May 3, 2006
    #7
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