My 04 Z71 with dual climate controls started acting odd this summer. One day it was blowing hot air when the AC was on and temp was set in the 60's. I just turned the system off, and next time I started it up it was functioning again.

Lately I started noticing the heater was blowing cool to lukewarm air with both sides set to 72. If I set either side to 80's, it would blow warm air.

I found a solution that worked for me (damned if I can find the post now) and thought I would repost it to offer an easy fix if you're having the same problem.

* key OFF
* open the FUSE panel just inside the driver's door
* remove the 10 AMP HVAC fuse (it should be GOOD, but check it anyway)
* turn the KEY to the accessories (not start/run) position, leaving it that way for a minute or so
* turn the key OFF
* re-insert the 10 AMP HVAC fuse

Doing the above apparently allows the "actuators" to be reset.