2001 Cadillac Catera auto temp controls

The heat in that vehicle is controlled by a blend door that regulates heated air flow. It is operated by an electric motor/actuator. The problem can be that the actuator is stripped or inoperative or the door itself could be damaged. This is what needs to be determined by examining the actuator and see if it is responding to heat change commands or not.
This would require dash diss-assembly and some real body manipulation to reach it so it may be a job for the dealer.