GMC Truck Forum banner

1 - 3 of 3 Posts

·
ɹǝqɯǝɯ sɟɯb
Joined
·
1,791 Posts
Discussion Starter #1
In the last few weeks I've noticed my heater takes a while to "kick in". For example you would think once the engine reaches operating temp you should have no trouble warming up the cab interior. Even with my truck at 180-190 degrees the heat still blows cold. As soon as I begin to drive and reach 35-40mph it's like a switch is turned on and instant heat. It seems I could travel all day long below 35 and my heat would never work. I wouldn't think a thermostat would be affected by driving speed.

So is it electronic? What gives?
 

·
Registered
Joined
·
155 Posts
It's not the thermostat, check the heater hoses when the truck is warmed up. They should be hot to the touch. If both hoses are cool, check the heater control valve, it is probable stuck. If the inlet is hot, but the outlet is cool, you most likely have a restriction in the core. If both hoses are hot but still only cool air, check the blend door operation in the cab.
 

·
|=====TK=====|
Joined
·
523 Posts
Your truck sounds like it is running a little cool. I thought on these newer trucks they ran a little over 200-degrees. Anyhow, I just went through all kinds of heater problems on my '05. They were all covered under warranty but was still a mess. In the end the dealership replaced (3) HVAC actuators and fixed a loose ground at the fuse panel. The controls on these newer trucks are all computerized (except for the blower motor speed), and if something gets goofy with the computer or a sensor you will have all kinds of problems.

Try the tests in the above post first, but if you can't find anything you may need to have it hooked to a diagnostic computer to read what is going on. -TK
 
1 - 3 of 3 Posts
Top