Question about 1999 GMC Envoy

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Hot to cold air in 1999 GMC Envoy

My girlfriends 99 GMC Envoy goes from blowing warm air to cold to warm to cold when on warm air setting. Loaded Envoy with climate control. Any ideas?

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  • 308 Answers

Heater core plugged. remove heater hoses, use tap water to flush out core..

Posted on Jan 17, 2013

  • 4 more comments 
  • Ben Havlicek Jan 17, 2013

    Been down that road. Flushes fine. Heater core is fine as both hoses are very hot going in and out.

  • Ben Havlicek Jan 17, 2013

    I get heat then cold ait, then heat then cold air. Fluctuates every 3 seconds.

  • Adrian Jaramillo
    Adrian Jaramillo Jan 17, 2013

    blend door problem for cold hot air flow..actuator problem..common..

  • Ben Havlicek Jan 17, 2013

    i think the blend door is fine as it is going from hot to cold.

  • Ben Havlicek Jan 17, 2013

    what is making it do that though? Ambient air temp sensor?

  • Adrian Jaramillo
    Adrian Jaramillo Jan 18, 2013

    make sure your thermostat is operating. blend door actuator allows cold-hot operation. if blend door is working, and both heater hoses are good and hot, then possible blend door it's self may be sticking or resticted to opening properly. ambient temp sensor only controls ac operation due to real clod weather. has nothing do with heater operation.actuator is located behind blower motor. can be replaced with out dash removal.7\32 screws (two) hold actuator into place. remove connector, remove actuator. align oval male stem comming out of blend door on to actuator. may have to manualy move beld door oval to align.when blend door actuator was on its way out, it hads a snaping sound comming out of it when vehicle is shut off. even if heater was not used. let me know if i can help with any more possibilites.

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