There are eletrical motors called actuators that control the temp doors. There are two temp door actuators, one for the drivers side and one for the passengers side. Inside the actuators are sensors that tell the a/c controller where thay are at (hot/warm/cold positions). When the actuator sensor goes bad, the a/c controller will command that actuator to full hot mode untill the key is cycled. The only repair is to replace the actuator that is bad.
let me know if you need more information.
The actuator on the drivers side is easy and sould cost around $150 for the labor, the passengers side is not easy, you have to remove the upper dash labor should be around $450.
The parts are around $260 at the dealership. you can get them on e-bay cheaper, not sure how good they are. I would get a GM actuator for the passengers side, you do not want to pay to have to replace this part again because of some cheap part.
The drivers side can be chaged by a person with some skills, not that hard to replace. let me know if you would like instructions.
Instructions will be great!!!!!! I await your reply.
Thank you so much!!
Remove the insultaor panel under the passengers side of the dash.
Just in front of the center console under the dash is were the actuator is located. Its held in with two screws, you will need a 5.5mm socket to remove the screws.
Remove the eletrical connecctor and then remove the actuator. Replaced the actuator and reinstall. The actuator is number 2 on the diagram below.