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???