Climate control suddenly blows cold air with heat on

[ree]

Twice in the past month, I've been driving along with the heater on (no defrost) and, all of a sudden, the climate control starts blowing really cold air. No amount of futzing with the controls gets it to blow warm. In both cases it started acting normally after stopping and restarting the truck.

Clearly there's something whacked in a computer. Would a code have been thrown for this sort of event to help identify why the climate control felt it needed to blow cold air? If so, how many ignition cycles do I have to get it to a dealer to read the code and diagnose the problem?

Perhaps it's time to order my own programmer.

If no codes are involved, how the hell should I get this diagnosed and resolved. It's a very spurious problem. I'm sure it'll never reproduce at the dealer. And should I worry about the AC compressor cycling when it's sub-freezing when this happens???

[Adam in CO]

Radiator problem. Check the coolant level, for leaks, for radiator or hose blockage. No coolant means nothing flowing to heater core. There wouldn't be any codes.

[ree]

Originally Posted by Adam in CO

Radiator problem. Check the coolant level, for leaks, for radiator or hose blockage. No coolant means nothing flowing to heater core. There wouldn't be any codes.

Rebooting the truck would fix a low radiator level or a blocked hose? I'll check, but it seems to infrequent to be this. Also, the coolant temp looked normal in both cases.

[timgco]

I believe there are TWO plunger switches under the dash that go bad. I have the same intermitent issue as well on my 06.

[BlueHUMMERH2]

Yeah, take it in and have the blower box checked. There may be a blockage or some kind of debris that is keeping the flap from opening/closing. I get leaves into my blower sometimes (I don't know how) and I've also had snow come inside.... But it's probably not anything more than the cold/hot flap thingy getting caught up.

When I had this problem, I was blowing cold on one side and hot on the other, if that helps. That's why I figured the diverting flap was stuck, and wasn't moving when I changed the A/C controls.

[Alan06SUT]

This happened to me when I turned one all the way hot and one all the way cold, then tried to turn them both back to hot, only the 1 hot side stayed hot. The cold side never got hot. The next day everything seemed to work fine??? So, how can you check the flap? I dont want to go all the way to the dealer.

[SnakeH2]

Originally Posted by BlueHUMMERH2

When I had this problem, I was blowing cold on one side and hot on the other....

That's happened to me a couple of times. I shut the whole system down and that seemed to correct it.