‘89 W900B manual fan switch not working

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by mile marker 27, Jun 24, 2021.

  1. mile marker 27

    mile marker 27 Medium Load Member

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    Well, maybe the switch is working, but the fan ain’t coming on. When I flip the switch to “on“, I hear air coming from a small valve towards the top rear on engine(DDECII). What’s going on?
     
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  3. roundhouse

    roundhouse Heavy Load Member

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    I’m not sure about your particular truck
    But usually the fan uses air pressure to turn it off and lack of air to turn it on, just like the parking brakes.
     
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  4. Roberts450

    Roberts450 Road Train Member

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    You’ve got a broken/leaky air line or solenoid. Charge up the air system, shut the engine off, turn the key back on and turn the fan switch on, locate the air leak, fix it and then retest.
     
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  5. mile marker 27

    mile marker 27 Medium Load Member

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    328CB335-73F1-4753-B057-F0E2F8D614BA.jpeg
    Did as you suggested and there’s some air coming from the top port on this solenoid. Anyone got a part number for this solenoid?
     
    Last edited: Jun 27, 2021
  6. roundhouse

    roundhouse Heavy Load Member

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    Dis assemble the solenoid and clean it

    Probabaly just has trash in it
     
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  7. mile marker 27

    mile marker 27 Medium Load Member

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    What’s the minimum psi, that the fan clutch can be engaged? What coolant temperature does the electric fan engage?
     
  8. Roberts450

    Roberts450 Road Train Member

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    The fan will most likely auto lock on around 100-90psi as they normally take air to unlock them and with the Detroit Id venture to so the ecm will probably turn it on around 200-210 but not sure.
     
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