Too much heat, CK1500

heating

#1

I have a CK1500, 2001 with AC. After driving 30-45 minutes it goes to full heat. Turning the heater control knob has no affect. Everthing works fine up to this point.

The heater/ventilation control module can be easily replaced but befor forking over 175 bucks for this I hope to verify whether this is indeed the likely culprit.

As cars and electronics go, it could well be something else hidden deep in the bowels of the dashboard.

Thanks.


#2

This could be a vacuum problem. If the temp control door, or flap, is vacuum actuated, and there is a vacuum, leak, the door will move to one extreme, which, in this case is full heat.

The temp control door directs airflow through the heater core or the AC evaporator, or a combination, depending on the desired temperature.

Does the throttle position have anything to do with this?


#3

The temp control door is electrically operated by a motor. It appears to work fine ‘in the garage’ and changes position depending on the heat control knob position.
Throttle has no apparent bearing.