I have an 08 gmc Sierra 2500hd gas. The heater quit working. I've noticed in the past few months during cold weather it would require extra attention to get to working. I would turn the center temp control **** back and forth and eventually it work get warm. No dice. After a 45 minute drive it never got warm. Anybody else have this issue? What was the remedy? I'd prefer to fix it myself if possible. Thanks

My WAG is duct servo(*) died or stripped out, or regulators are jammed. Without more detail I'd ask:

Is coolant full?

Does blower work?

Does heat come out anywhere (above dash, under dash, through upper vents, through heater vents)?

Does air come out anywhere (above dash, under dash, through upper vents, through heater vents)?

Thanks for responding. Yes the blower motor works...no..heat does not come out anywhere..yes coolant full. It'* a normal..running and driving truck. Heat just quit working.

One thing good to verify would be that both heater hoses get hot when the engine is warm and the heater is turned on.

Assuming that air blows out somewhere for this, and hopefully the output can be chosen (defrost versus dash versus floor).

I'd check the motor for the hot/cold regulator:

1. Disconnect power to the blower motor
2. Turn off anything noisy in the room/shop/yard
3. Turn on ignition but don't start engine
4. Let it get done chiming etc.
5. Turn blower on a notch or two, doesn't matter as the power is disconnected. The idea here is the HVAC system is on.
6. Set the output to floor
7. Set the temperature to cold
8. Listen under dash
9. Listen under dash as you change temperature from cold to hot
10. Do you hear movement?
11. Listen under dash as you change temperature from hot to cold
12. Do you hear movement?
13. Do it a few more times for fun or to be sure or etc.

If you hear movement, controls are likely good and wires are connected etc.

If not then possibly bad controls or disconnected wire or dead motor.

If you hear movement and it sounds like a slowly skipping gear then either the motor is shot or the point where it engages with the temperature door is broken or stripped.

A friend'* 2003 Avalanche had a stripped out motor on the one that regulates direction, so it always blew out of defrost and floor no matter what you chose. It had over 300,000 miles on it at the time and she didn't want to spend money on it and got rid of it a few months after that started. It always sounded like a gremlin was slowly turning a crank causing this never-ending subdued popping sound. I could make it stop by selecting the position it was stuck in so it wouldn't "try" any more. If you do have the popping sound, try to find the control adjustment that makes it stop. If you do, you have fairly good odds that it is the motor.

Disclaimer: I haven't worked on these things a lot like some folks here, I've just fiddled with a few as friends' cars have had issues. I'm just throwing my $0.02 in to get you going. Maybe one of the others will have some better advice.

Recently dealt with this same situation on a Ford (yikes) F150. The Ford would take 15-20 minutes to get any hint of heat coming out of the vents.......thirty minutes and it would be slightly warmer, but still would be blowing cold air. Once the truck was up to mormal operating temperature........still cold.

Turned out to be that the cooling system was full of corrosion build-up.

I would squeeze all the coolant hoses and it felt like, well, it felt like squeezing a balloon filled with sand.

I ended up removing all coolant hoses and bashing them on the ground until all the junk was dislodged from inside them.......I reattached the heater core hoses onto the heater core and clamped a garden hose onto the heater core hose.....turned the water on full blast and SLOWELY the water began to trickle out the oppisite side of the other heater core hose.

Eventually, a good stream of water was flowing thru the heater core. I reattached all hoses and added a chemical bottle of Prestone Radiator Flush to the cooling system.

Left that chemical stuff in there for a couple days and now the heater shoot flames out the vents......

Ok, well maybe that last statement was a bit of exaggeration, but the heater is now hot.....really hot.

Eventually, I drained and refilled the coolant with the proper coolant fluids, but this is how I got hot air back in the cab.

Like Cathedral Club said, first thing to do is touch BOTH heater core hoses.....if both hot, then you know the core is ok......if the inlet is hot and the outlet is cool, then either the core is air bound or plugged....in this case, do a reverse flush.....

If the core is ok, and you have good air flow, but no heat, then it is the temp actuator, the circuit, the control head, or worse case scenario, a binding temp door.....

I would remove the harness....there are 5 wires......one ground, one BAT source, one 5V ref, one control ground and one position voltage signal......the BAT, 5V, and ground are easy to check with a voltmeter......position voltage can only be checked with the harness connected, by back probing it......should be anywhere between 0-5V, and will vary when the door moves(but it is not moving at this time)......you can check the control line with a voltmeter.....it is normally closed to ground......but when the control head calls for a change in temp, the signal will go from ground to a voltage to the logic circuit in the actuator(this will have to be done while back probing with the harness connected)......

Personally, I would disconnect the harness, remove the actuator, and see if I can move manually move the door with the system running to produce heat....if you can, 99 out of a 100 times, it'* the actuator, as others have said.....just replace it....

Got a project now

I hope we've helped. Please let us know how it goes!