Question about 2001 GMC Sierra 2500HD

3 Answers

I hava a 2001 GMC Sierra which the heater intermittently gets stuck on full hot. This only happens when the heat control is turned to full hot and then I try to turn it down again. Sometimes it sticks for a few minutes, other times for a couple of days. At first it seemed to fix the problem when I shut off the truck and started again, but it has worsened and this does not work any longer. As long as the heat isn't turned to FULL HOT it doesn't stick and the temp control works. Everything else works. From researching this, it looks like a common problem but I'm not sure if its the actuator blend door or the heater control itself. It's not just one vent or another, it's all of them so if it is an actuator then it's the main one that contols air to all vents but I don't know where it's located.

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  • daksfossen Mar 13, 2011

    I guess I should clarify; the blower motor works fine. When I said full hot I meant that the air coming out is HOT!! I can turn the fan down (fan control works fine) but the air blowing out remains hot when the temperature dial is turned down.

  • daksfossen Mar 13, 2011

    The only thing is that the problem is intermittent. It's definitely electronic or something that can change in an instant because it sometimes corrects with simply shutting the truck and starting again. The A/C and the cooling fan work great. The only time there's a problem is when the temp control is turned all the way to hot and then I try to turn it down again. If I turn it only partially to hot (ie. 7/8 of the way) it does not stick. Thus I have learned to live with the problem by not turning it all the way to hot. But,.. I would like to find out what could cause the problem. I had a mechanic friend tell me that he thought it was the dash control head but I'm not convinced. I have read that the actuator doors can get stuck open which would cause the problem.

  • daksfossen Mar 13, 2011

    I hava a 2001 GMC Sierra which the heater intermittently gets stuck on full hot. This only happens when the heat control is turned to full hot and then I try to turn it down again. Sometimes it sticks for a few minutes, other times for a couple of days. At first it seemed to fix the problem when I shut off the truck and started again, but it has worsened and this does not work any longer. As long as the heat isn't turned to FULL HOT it doesn't stick and the temp control works. Everything else works. From researching this, it looks like a common problem but I'm not sure if its the actuator blend door or the heater control itself. It's not just one vent or another, it's all of them so if it is an actuator then it's the main one that contols air to all vents but I don't know where it's located.

    re-post

    The A/C and fan work fine. The issue only happens when the temp fan is turned all the way to hot and then I try to turn the heat down (If I only go 3/4 hot then it doesn't stick). Additionally, the problem may stop from shutting the truck off and starting again (but sometimes not)... which leads me to believe that it's electrical...

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One or more heater & A/C (HVAC) temperature and/or air delivery mode door actuator may fail, resulting in improper temperature or air delivery. If this occurs, fault code(s) should be stored in the HVAC control module which should assist in diagnoses.

Posted on Mar 14, 2011

  • Tre Elkins Mar 14, 2011

    the
    blower module that is located at the bottom of the heater box, next to
    the blower motor, above the panel below the glove box, has a tendancy to
    go bad, possibly overheat, and melt the larger of the two connectors.
    This can lead to one or all sppeds inop. the module will need to be
    replaced, and th connector inspected. If the connector is melted, or
    discolored, it needs to be replaced. A pigtail with wires, and
    connectors, as well as the resistor, should be available at a local GMC or Chevy dealer. Good luck

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Sounds like it could be the high speed relay for the blower motor. Try tapping on it when it's acting up. If it helps at all, you may want to change the relay.
Thank you,
Lee

Posted on Mar 13, 2011

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Hi, there are several reasons your vehicle may be blowing hot air through the vents, such as a need to recharge refrigerant. There could also be a problem with the air conditioner's compressor. Vents will blow hot air if the compressor does not activate when the A/C is turned on.

Compressor To find out if the air conditioner's compressor is causing hot air to come from your vents, you can test it by connecting its clutch wire to a battery. If the compressor fails to turn, it is likely that you will need to have it replaced.

Refrigerant If your air conditioner is low on refrigerant, it can be recharged to combat this issue. However, checking for leaks should always be done before taking this action. Also, your air conditioning system's vacuum should have all air removed from it prior to recharging refrigerant.

Posted on Mar 13, 2011

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