I am trying to figure out where to start looking. My '95 GMC Suburban will only shut the hot air off when it is cold enough outside to trigger it, my guess is that the heat is making something too hot for it to flip to cool air. Right now it doesn't matter whether the temp control is on red or blue, it is always hot. Also the lower heat will only shut off if you run the controls on face level and flip the speed to on. When it is cold outside you can hear the lower flip shut when you change the location. I am making a guess that the actuator is bad that controls the lower center vents / air distributor. Anyone have any idea though why I cannot get the heat too change to cool air? At this point if the A/C is working it can't get through the hot air. Many thanks!!