95 GMC Burb heater won't shut off.. Help!

**bluecow24** · 12-29-2008, 10:38 PM

Hello everyone, new member here. We picked up a '95 GMC 2500 to tow with recently and found an issue with the heater in the truck. First trip I took it on that was about 15 miles I couldn't get the heat to shut off even with the switches shut down. The truck sat for a few days before I had it out again and I didn't really notice the problem, same for probably the next month, but I usually am only running back and forth on short trips with her. This past weekend we took a long trip and after the engine warmed up we found that no matter what you did you cannot shut the heater off (you can flip the vents closed but they still try to blow hot air). The heat is almost hot enough to melt your sneakers to the floor, the heat is mainly coming from the two black open ducts that are near the trans tunnel (no shut off for these from what I can see). After trying different positions with the switch we were able to get it to a low speed from those ducts but still very hot. To ride in it you have to run with the windows down otherwise you will be soaking wet.

I haven't been able to find a haynes manual or anything local yet so I plan to order one, but does any one have any ideas of where I should start? At this point I can't even tell if the A/C works or not because it won't stop blowing hot air. The rear vents do blow a cooler air but it feels more like outside air temp to me.

Many thanks, Michelle

**ct9a** · 12-30-2008, 01:16 AM

Welcome to the site.

My burb has hot air that comes in through those vents too when the blower is shut down, though not that much and not that hot. I'm thinking that it may be a stuck door in the HVAC piping, that would be my guess.

**bluecow24** · 12-30-2008, 01:07 PM

Would this be something I check out from inside under the dash? Today I was out and when I first started it up I was able to shut the heat off and the blower shut off properly. Could the door possibly move enough sometimes to work properly? Thanks.

**vncj96** · 12-30-2008, 01:15 PM

Maybe try and disconnect the battery and /or pull the fuse and see if it can reset itself

**unplugged** · 01-01-2009, 02:24 PM

Probably a stuck heater control valve. See this earlier post
Easy replacement. For an online manual check out dwill3015's post here

**alp2001** · 01-01-2009, 06:22 PM

Had this same problem on my 2001. Ended up having the heater control valve (vacumn actuated inline gate valve) replaced. Was covered under warranty but didn't look to expensive or hard to do yourself.

**bluecow24** · 01-05-2009, 08:11 AM

I thought maybe it was one of the actuated valves, I looked over the diagram in the LMC catalog that I received and had a feeling it could be one of those. Hopefully it will warmed up a day or two so I can check it out, right now it won't fit in the garage so the great outdoors is the workplace. Thanks for the link for the online manuals, that is awesome! Again, many thanks!