12.7 Detroit Fan Switch

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by GliderKitTrucker, Sep 25, 2020.

  1. GliderKitTrucker

    GliderKitTrucker Bobtail Member

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    Wanting to wire a manual fan switch on a series 60 12.7. Wondering if any mechanics would have any insight. I know you would wire from switch to fuse panel for power but where would you wire to to complete the circuit? Would you wire to the solenoid?

    I do know that there’s two types of circuits, one normally open and one normally closed. How do you tell which one you have?

    With the engine off and belts lose the fan will free spin if this helps any.
     
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  3. Hulld

    Hulld Road Train Member

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    What make and model truck are you working on?
     
  4. GliderKitTrucker

    GliderKitTrucker Bobtail Member

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  5. Hulld

    Hulld Road Train Member

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    Not sure on a western star.
    On my Freightliner Columbia when you remove all wiring from the fan solenoid the system reverts to the fan being engaged.
    My Columbia has key on power on one side and a ground provided by the engine controller.
    When the controller wants to turn the fan on the controller interrupts the ground circuit causing the fan to come on.
    To figure out if yours is set up the same find you fan solenoid and with the engine running unplug it at the connector.
    If the fan then comes on all You have to do is put a switch in series circuit with either wire going in to the fan solenoid.
     
  6. GliderKitTrucker

    GliderKitTrucker Bobtail Member

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    Okay 10-4. I appreciate the advice
     
  7. Hulld

    Hulld Road Train Member

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    I believe most operate the way mine is.
    They are purposely designed that way so if there is a catastrophic electrical failure the fan reverts to on and the engine wouldn’t over heat.
    Let us know how you make out.
     
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