Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
This is actually a common problem with these trucks. Most likely it is not the control head. There are actuators (motors) that turn the doors inside the a/c box to change the temp. If the control head sees that the actuator has gone to far (also known as over travel) it defaults to the hot position. There is a reprogram that can be done at a dealership that should fix this. You would need a GM Tech-II scanner to get the codes from the a/c module. Here is the GM service bulletin for this concern.
Some customers may comment on one or more of the following concerns:
This condition may be caused by the Heating, Ventilation and Air Conditioning (HVAC) actuators that may hunt for the correct commanded position. This cycling may cause a clicking or ticking noise.
An overtravel of the HVAC system control doors may cause one or more of the concerns listed above. If an overtravel occurs, a Diagnostic Trouble Code (DTC) will be set, and the door will go to a preset default position. When a system door defaults, that door will stay at the default position until the DTC is cleared. After the DTC is cleared, the door will operate properly until the overtravel condition re-occurs.
The following table lists the HVAC system doors and the DTC associated with it.
Air inlet door (recirculation door)
Left temperature door
Right temperature door
Front system mode door
Technicians are to perform the normal diagnostic procedures in SI for these concerns. If diagnostics show that the HVAC system door(s) travel below 5 counts (out of the lower range) or above 250 counts (out of the upper range), then update the software calibrations in the HVAC control module. The new calibrations were made available to dealerships as part of TIS2000 incremental satellite update version 2.5, which was broadcast to dealers in February 2006.
The new calibrations have been updated to compensate for the actuator overtravel condition, the actuator hunting and the ticking/clicking noises. The new calibrations effectively eliminate the codes listed above, the default position of the doors associated with the DTCs and opens up the feedback position value. The new calibrations should not be used unless the vehicle has one or more of the customer concerns listed above or a DTC listed above has been set. The new calibrations will not correct any other DTC or A/C system performance concern.
Most of the time it would be either one or the other, not at the same time. One other thing you can try is wiggling the wires on the connector at the right side instrument panel. There is a panel on the right side of the instrument panel in the same place as the fuse panel on the left side. Remove this panel and you will see a black junction box with several pugs in it. The plug that is in the lowest position is for the actuators. With the truck running and the a/c on, wiggle the wires on this plug. If wiggling these makes the temp change, then you need to adjust the terminal tension on this connector. This can be done by unplugging it and use a small pick to bent the inside of each female terminal to make its opening smaller.
If this is not the case I would get it reprogramed, or at least have it scanned for codes and let me know what they are.
I hope this helps.