I have a '05 GMC Sierra, crew cab, 5.3, auto tranny, with about 150000 miles on it. AC control panel has two round dials, with two hot/cold sliding controls. Out of no where, the ac started blowing hot, really hot air. I pulled over and checked under the hood, the belt is good, the compressor was running, (so i ruled out the low pressure switch). The ac continued to blow hot, alot hotter than the outside air which was at 104 at the time. I checked all the controls and they were set correctly. i turned the ac off and drove for about 15 miles and tried it again, still blowing really hot air. I parked the truck for 2 hours and tried it again... now i have cold ac, just as cold as its always been. I'm on day two with the ac working as it should. Can anyone tell me why the ac blew hot, really hot air? I can only think that maybe the door under the dash that allows the ac cold air into the cab closed and allowed the heated air from the heater into the cab??? Any answers would be appreciated. thanks.
theres a software update for the HVAC controls. sometimes when you put it on full hot or full cold, the position sensors in the blend doors will open past the normal range for the sensors to read, it sets a code and defaults to hot.
GM bulletin #06-01-38-003 if you want to look it up
This happened a few times in my 03, if turning it off and back on doesn't work. Unhook the battery for 3 mins and that always worked for me. Whenever you can take it in to the dealer for an update on the software.
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