I noticed last night with heat on all the vents on top of the dash and base of winshield stay cold. When I manualy instruct the system to floor vents only there is still cold air comming from the dash registers and demister and defroster vents. Could this be one of the actuator motors? There are no codes so I am baffled. I've replaced the aux coolant pump thinking thats why I had low heat. The heat now is great on all the lower registers but the top ones are always cold. I dont know if this will help but after a long drive on the highwaywhen I slowdown for an offramp the air from the top vents gets colder. Am I going crazy? One thing for sure my face is cold even with the dash register wheels turned to full off. Still getting cold air from defrost and demist. Where should I look??

 

What happens if you have it on "Auto", or is your first sentence what actually happens on "Auto". If so it seems there is flap not moving. I don't think the Climate Control has fault detection, but I may be wrong.

 

In auto or manual the top dash demist and defrost always stay cold along with warm heat from floor registers even when set to hi heat. I was told that the evaporator temp sensor could be bad. Has anyone had a bad evap temp sensor before that caused this type of problem?