heater and AC problem on 2003 Ford Windstar

Heater does not operate. A clicking noise is heard behind the heater unit once the lever is slid to adjust the temperature. Blower is working, but no heat. Additionally the AC functions only if the lever is located in one spot on the temperature gauge. Can not adjust the coldness. The clicking noise is also heard if the lever is not on the one spot so the AC can operate. Not sure what will be needed to get both heater and AC functioning properly.

Asked by for the 2003 Ford Windstar
There is a module located behind radio. Go to parts store buy the radio puller wires,they fit in the 2holes on each side of radio,stick them in at same time then pull out radio.Then you can see the black square module bolted in behind there,this opens and closes the "door" when you slide your a/c controls to hot or cold. It has plastic gears inside this box ,they wear out and the door will stay shut when broken. no heat in winter .Auto parts stores have the module. i took old one out couple of bolts hold it in.I used real long ext on socket wrench to reach bolts,kind of tight spot. then show them. easy to remove and install,when installing make sure a/c control is slide to left. so the gears can align.
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van has actuators that control blend doors to direct air. actuator or blend doors could be the problem