2005 GMC ENVOY
96,000 MILES
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My 2005 gmc envoy....sometimes the heat and defrost work, and at other times the heat and defrost don't work. What is the problem and is it an expensive problem? I just had the thermostat replaced.....
Nov 25, 2012 at 5:08 AM
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DRCRANKNWRENCH
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I am giving you a diagnsotic walk thorugh for your situation. Just use the link below to get to it.
I believe you have a bad actuator for an air control door or a braken air control door.
Here is the link;

https://www.2carpros.com/articles/car-heater-not-working
Nov 25, 2012 at 5:14 AM