Blows Constant Heat!! Please Help!

My 1991 Cutlass Supreme blows heat continuously. This happens regardless of the fan being on or off. The thermostat on the AC control unit does not adjust the temperature. The faster the car is moving, the more heat blows in. I’m assuming that there is a damper motor is stuck open. Or is there something else that could be causing the problem? Where is the motor located? Thank you for your help!

Welcome to AF, the issue with constant heat is either the dash temp control unit is bad or the temp door is stuck in the heat position, not advising guess work here but the dash units were prone to failure, check the temp door first.

Thank you for your help! I'm assuming that it is temp door because heat does not blow in when the car is not moving. Where is the door? Is it under the glove box? Thanks again!