I have a 92 5th ave, and the heat is blowing hot all of the time, even if you turn it down on the controller. we tried another controller from a different car. what actually receives the signal from the controller and commands how much heat is supposed to come out?

thanks,
Chris

 

Inside the plenum is a "blend door", a flapper that moves to control the mixture of cold and warm air. There's an actuator that moves the door. That actuator is what the controller sends its signal to.
There are at least three "doors" in there: the blend door, the "mode door" (which sends air to the floor, panel openings or defroster as required) and the "recirc door" (which brings in outside air unless "recirc" is selected). By process of elimination you should be able to figure out which is which while observing them go through their gyrations.