1999 Pontiac Grand Am Climate Control Problem

The temperature is controlled by the use of an air mix door that is operated by an electric motor/actuator. This door can be jammed or the actuator can be inoperative or have stripped plastic gears internally. It can also be the control head sending mixed signals to the actuator. I would get it in one position or the other and then unplug the actuator and see if it remains at that setting. If so, it's likely either the control head of a temp sensor it monitors if it's an ATC system. It will require a Tech2 scan tool if it's an ATC system.