Has anyone else had this problem. I recently bought a 99 Navigator and I can not get the heat to turn off. The fan controls work fine, but no matter how low I set the temperature it blows hot air. Even if I just run the vent it still blows about 80 degrees even when it is 40 degrees outside. Any Ideas? Thanks for the help.

 

It may be the door in the air handler. Our '97 Expedition encountered this problem last year.

There is a door in the airbox which shifts back and forth to direct either hot or cold air through the system. Unfortunately, the door is rotated via a plastic extrusion that fits into a motor. Over time, the plastic can break- which leaves the door stuck in one position. Ours was also stuck on heat.

Hopefully, Ford changed the mounting between 97 and 99, because getting to ours required removal of the entire dash.

Its also possible that the motor that moves the door has been worn out. All you have to do is locate the motor (on the bottom of the air handler), remove a few screws, and see if the motor turns when you switch from hot to cold. If it does, I would bet its the door.