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Thread: Auxillary fans not working 92 model

  1. #1
    E500E Guru sheward's Avatar
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    Auxillary fans not working 92 model

    Reading through past threads on the subject left me with questions. I have verified the strip fuse is good. Resistor is new. The fans do not operate on low speed or high speed with engine at operating temp with A/C on or off. Both fans operate when powered at the connector behind the drivers side light. The fans do operate when the two white blade connectors in the same location are jumpered. Do I understand correctly that unplugging the coolant temp sensor should enable the fans with the key on? If so, does this indicate a faulty sensor? How would I verify if the problem is the "dual cube relay" behind the fuse box? On a side note, does anyone have a picture/description of what all the cube relays control in this location or where I might find one? Again, this refers to a 92 model.

    drew
    Last edited by sheward; 2 Weeks Ago at 04:36 PM.
    Drew
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    E500E Guru emerydc8's Avatar
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    Re: Auxillary fans not working 92 model

    Pulling the coolant sensor connector with the key on should cause the fans to go to high. I don't think this would necessarily indicate a faulty sensor because the low speed fans are controlled by the pressure switch on the AC accumulator. If you can get the fans to high by pulling the coolant sensor, I would look into the low speed control side (refrigerant low?/bad connection on resistor?). I have had the wire going to the top terminal of the resistor disintegrate on me numerous times due to excessive heat.
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    Last edited by emerydc8; 2 Weeks Ago at 04:34 PM.
    Jon D.
    1994 E420
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    E500E Guru sheward's Avatar
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    Re: Auxillary fans not working 92 model

    Thanks for the reply, Jon. Should they run this way regardless of coolant temp? Car is cold presently. Edit: OK, they do operate. Does this leave me with a faulty relay?

    drew
    Last edited by sheward; 2 Weeks Ago at 04:44 PM.
    Drew
    92 500e 58,500 miles
    92 500e 180,000+ miles
    93 500e 179,000 miles sold
    92 500e 110,000 miles sold

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    E500E Guru emerydc8's Avatar
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    Re: Auxillary fans not working 92 model

    I would focus on the low side control then. I think the coolant temp sensor on the intake, when hot, essentially opens the circuit and causes the fans to go high. That's why pulling the sensor terminal simulates this same condition. Are you getting 12V to the terminal at the top of the resistor? I can't remember what the '92 fuses look like but have you gone in behind the fuse box and checked the ice cube relay? On the later models there is a fuse.

    You can jumper the wires going to the AC accumulator and bypass that switch to see if that's the problem (not the sensor itself but the wires going to it). If you can get low speed fans by doing this then I think either the freon is low or the sensor switch is bad. Otherwise maybe it's the relay. If I recall, when you jumper the wires you should hear the relay click. If there's no click, the relay could be bad. I'm sure Dave will chime in here.
    Jon D.
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    .036 Hoonigan™
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    Re: Auxillary fans not working 92 model

    Drew, as Jon said, if you pull the coolant temp sensor (2-pin) at the intake manifold and the fans run on high, that proves the fans & high speed circuit are ok.

    It wasn't clear if you jumpered the wires at the receiver/drier pressure switch, the red one with pigtails... if you jumpered those and the fans run on low speed, the low speed fan circuit is also fine.

    The fans run on low speed based on refrigerant pressure, not when the AC compressor is running. The red switch triggers on at 16 bar, off at 12 bar. You would need to connect AC manifold gauges and see if the high pressure side is exceeding 16 bar and the fans still not turning on. If so, the red switch is likely defective, which requires evacuating the system to change it.


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