IrishJoe

Hey all, have been chasing this problem for months, hoping someone here knows the answer. The issue is that my blend door goes full hot, regardless of the controls. This is not a problem with the blend air door actuator. Please continue to read:

2002 Chevy Suburban with rear AC. Does not have the true automatic HVAC controls, just the single zone with the "auto" capabilities. I have replaced the blend door actuator 3 times, the last 2 times with GM parts from GM. I have replaced the HVAC controller twice, both times with GM parts. Both the actuator and the control unit have since been installed in another rig and verified that they work. I have tested all the wires for the system repeatedly, working through the factory steps to confirm voltages. I have proper power and ground where I'm supposed to, I have continuity where I'm supposed to, everything has been tested with a conventional bulb test light to avoid false positives. Everything tests properly. I have re-synced and reset the HVAC controller per the factory procedure.

If I use a pair of pliers to manual force the actuator to the cold position, then plug it in, the HVAC controller will command a move to full hot, and the actuator will respond and move the door to full hot. Then it won't move again.

Based on the fact that it will reliably move the actuator to full hot, it seems like there is some emergency system that is overriding the controls and putting the system into full heat for safety. There is no such system that I can find in Chevy's documentation, but I cannot think of anything else that might be causing this.

Anyone heard of anything like this before? Anyone got any ideas on what to test next?

Thanks

Cusser

Use the pliers to turn to the cold position, unplug the actuator harness.