2008 GMC 2500 that intermittantly goes full hot on the passenger side

Dean E

Active member
Mar 30, 2022
165
64
28
Blair, NE
Gents, sorry I have not been on the forum in a while. My 2008 GMC Duramax is running like a champ. I did notice something on the last two big trips I have made with the truck. It takes a few hours or running but I have noticed that my cabin temp control for the passenger side will change to full hot uncommandedly. I do not have dual source selected but even when I switch it over to dual source nothing changes on the passenger temp. I ended up closing the passenger vents to control the temp in the crew cab and when I got home, I shut down the truck for about 15 minutes to unload stuff and then started the truck up again to put it away. I checked the passenger vents and again it is blowing cold like it is supposed to be. I had a 2009 Impala that had issues with the torquer motors for the cabin temp. When I first started it up they would clack, basically jumping gears for a while. This is different. I never get any noise but I will start to get a warm draft in the cab and then is when I realize the passenger vents are blowing very hot. Has anyone seen something like this? I am thinking about checking on line to see if this truck has those same torque control motors and see if that makes any difference. Dean
 

2004LB7

Super Moderator
Staff member
Dec 15, 2010
8,635
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Norcal
Used to get something like that in my LB7. A quick pull of the HVAC fuse and it was back to normal. Would happen once a year or so. As long as the fuse truck worked, I didn't care.

I think the process was to pull the fuse for 30 seconds. Then turn on the ignition but don't turn on the AC or blower. You might hear the blend doors moving. After a minute.or so, when it's finished leaning the positions, you can turn it all on to test

Not sure if this works on the later models, but easy to check
 

Dean E

Active member
Mar 30, 2022
165
64
28
Blair, NE
Used to get something like that in my LB7. A quick pull of the HVAC fuse and it was back to normal. Would happen once a year or so. As long as the fuse truck worked, I didn't care.

I think the process was to pull the fuse for 30 seconds. Then turn on the ignition but don't turn on the AC or blower. You might hear the blend doors moving. After a minute.or so, when it's finished leaning the positions, you can turn it all on to test

Not sure if this works on the later models, but easy to check
Yeah, that is the relearn process. The problem is the system works perfectly fine for a few hours on the road and then wham, the passenger temp goes full hot. Watched some YouTube videos. The passenger temp position motor is just under the passenger side air bag. I;ll think I will order one of those and give that a shot. I'm sure it is cheaper than replacing the cabin temp controller. Dean