Just thought I'd post this in hopes it will help somebody else out. I've got an '01 Explorer I bought used a few months ago. (This truck had been in a minor front end collision prior to my buying it so some work had been done up front.) It DOES NOT have the Automatic temp control on the heater. It is the one with the 3 **** control. It was stuck on defrost. Temperature control worked fine. You just couldnt get air out of anything but the defrosters. I got to checking it out and decided I wasnt getting vacuum to the position control ****. traced out vacuum lines from the intake manifold down to the little ball shaped vacuum reservoir that is located underneath the radiator overflow bottle and the washer reservoir. You can get to the reservoir easiest by takeing the 2 hex head screws out of the very front of the RH inner fender and then pulling the inner fender down. There are 2 screws that hold the reservoir to the inner fender. There are 2 vacuum lines that go to the reservoir. Apparently there is a check valve in one of the ports on the vacuum reservoir. I found that the vacuum line coming from the intake manifold had good vacuum but did not have vacuum on the other port of the reservoir. I switched the position of the 2 vacuum lines on the reservoir and the heater control worked as it should. I suspect that when the repairs were done to the front end after being wrecked that someone had connected the vacuum lines wrong on the reservoir. So...........if youre having the same issue with your heater position control and suspect or know that it has been hit in the front end at some point...............Might be worth a look.

 

Good tip. You never know what you'll find after it's been to the body shop.