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Heater-Air Conditioner Fan stuck on High. Kenworth T800

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by PyroJim, Jul 27, 2018.

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  1. Jul 27, 2018 #1
    PyroJim

    PyroJim Bobtail Member

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    The air conditioner-heater blower is stuck on full blast. The local dealer replaced some sort of module and that didn't fix it. Has anyone else seen this problem and have a clue? The local dealer is stuck. This is on a 2016 T-800.
     
    PyroJim, Jul 27, 2018
    PyroJim, Jul 27, 2018
    #1
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  3. Jul 27, 2018 #2
    Roberts450

    Roberts450 Road Train Member

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    Will it shut off? If it shuts off but only has hi when its on then the resistor pack needs replaced as thats what give the lower voltage for the other speeds.
     
    Roberts450, Jul 27, 2018
    Roberts450, Jul 27, 2018
    #2
    p608 Thanks this.
  4. Jul 27, 2018 #3
    PyroJim

    PyroJim Bobtail Member

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    It will not shut off. It's on anytime the key is on. The fan knob rotates and feels fine, but that baby blows full blast no matter what. Is this a 4 seasons unit on the KW? Doesn't it have a "high speed relay"? I'd like to see the schematic and see what's kicking the high speed relay on, if that is what it is.

    If anyone has a copy of the wiring diagram for a T800, I'd love to see it. Thanks.
     
    PyroJim, Jul 27, 2018
    PyroJim, Jul 27, 2018
    #3
  5. Jul 27, 2018 #4
    Roberts450

    Roberts450 Road Train Member

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    I would try unplugging the fan knob as it might have shorted out. If it still stays on then there is something else hooking the wires together somewhere and that means its time to get out the mulitmeter and check the wires and start tracing them to find the bad spot.
     
    Roberts450, Jul 27, 2018
    Roberts450, Jul 27, 2018
    #4
  7. Jul 27, 2018 #5
    PyroJim

    PyroJim Bobtail Member

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    Do you know if this vehicle has a high speed fan relay or not? Im wondering if it has fused closed.
     
    PyroJim, Jul 27, 2018
    PyroJim, Jul 27, 2018
    #5
  8. Jul 27, 2018 #6
    Roberts450

    Roberts450 Road Train Member

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    I do not. I know @pushbroom knows the Peterbilt's and Im guessing the KW's might be simular.
     
    Roberts450, Jul 27, 2018
    Roberts450, Jul 27, 2018
    #6
    pushbroom Thanks this.
  9. Jul 27, 2018 #7
    pushbroom

    pushbroom Road Train Member

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    Last six of the s/n?
     
    pushbroom, Jul 27, 2018
    pushbroom, Jul 27, 2018
    #7
    SAR Thanks this.
  10. Jul 27, 2018 #8
    PyroJim

    PyroJim Bobtail Member

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    2016 KW - 138781
     
    PyroJim, Jul 27, 2018
    PyroJim, Jul 27, 2018
    #8
  11. Jul 27, 2018 #9
    pushbroom

    pushbroom Road Train Member

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    Heater motor is PWM controlled from the cab HVAC control unit. Linear power module sends the appropriate signal to the motor as requested by the HVAC control head.
    Unplug the plug off the back of the HVAC control panel. If the motor stays running I suspect a faulty power module. If it quits possibly an HVAC control head.
    The other option is that the constant power for the power module (ORN7210) has shorted across to the motor power feed (YEL7210). Usually wiring issues in cabs are minimal.
    Diagram attached.
     

    Attached Files:

    pushbroom, Jul 27, 2018
    pushbroom, Jul 27, 2018
    #9
    RubyEagle and SAR Thank this.
  12. Jul 28, 2018 #10
    PyroJim

    PyroJim Bobtail Member

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    Thank you. That helps. I'll dig into it.
     
    PyroJim, Jul 28, 2018
    PyroJim, Jul 28, 2018
    #10
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