Vents blowing hot air all the time

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by kestrel1, Jan 24, 2021.

  1. kestrel1

    kestrel1 Bobtail Member

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    Jan 1, 2009
    Sacramento, CA
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    Just thought I’d throw this one up here in case there’s a simple fix before send it to the shop. My 2016 KW T880 is constantly putting hot air though the vent. Even when I have switch on cold, and fan off, the cab gets too hot as there’s a steady flow of hot air coming though.
    Anyone else ran into similar issue or any idea on the issue?
    Thanks
     
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  3. kwcam

    kwcam Light Load Member

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    Dec 29, 2012
    at the shop
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    Most likely the heater control valve has failed, see if the is a manual valve on the heater hose line that can be turned off will confirm it.
     
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  4. JonJon78

    JonJon78 Road Train Member

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    Possibly a blend door issue
     
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  5. Brandt

    Brandt Road Train Member

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    If your someplace still warm this time of the year. Nothing might be wrong. Their always seems to be some hot coolant flowing thru the heater core. Unless your truck has the manual shut off valves to cut all the coolant flow off you will get hot air at about 68F outside temp I usually find. It only a problem if you a/c is not working and you go south on the winter. That how freightliner is anyway.

    It could be something like others already said if you don't have any control of heat and it's winter.
     
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  6. MRMTRANS

    MRMTRANS Light Load Member

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    Apr 28, 2015
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    On my Freightliner C120, I have an electronic water control valve, which shuts the the coolant off from flowing to the heater core when on cold. It is controlled by a cab thermostat, which in turn is controlled by the the temp control dial that has a registered. I don't know about newer KWs, but I bet the system is electronically controlled. In which case, it could be a one of 3 parts that failed, like mine. Mine failed in the thermostat, and it defaulted to heat all of the time.
     
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  7. MRMTRANS

    MRMTRANS Light Load Member

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    Apr 28, 2015
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    I meant to say resistor, not registered. Stupid autospell!
     
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  8. LateNightCable

    LateNightCable Light Load Member

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    Feb 16, 2018
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    I drove a 2016 Kenworth T680 for awhile that had this same issue. Always blew hot air, even with the HVAC ‘off’. I got to driving around in winter, putting the windows down every few minutes to vent the cab.

    The company shop didn’t fix it. I just remember them saying it didn’t throw any codes when hooking it up to diagnostics.
     
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  9. kestrel1

    kestrel1 Bobtail Member

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    Jan 1, 2009
    Sacramento, CA
    0
     
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