Re: F150 Blender
It does have a blender door. It is electrically actuated, so check the switch, then wiring, then the actuator itself. Those actuators are known for breaking, and the new replacement ones are a bit beefier. There is a lot of wiring involved in the system because of harnesses and such (makes it easier for them to build), and they are also notorious for chaffing wires apart. You'll have to remove the dash to check the wiring and the blend door/actuator, so I hope it's the switch. There's a lot of man-hours involved in removing/replacing a dash!
First to check the switch, pull off the panel around the stereo and A/C controls; remove the screws holding the controls in; remove the hot/cold fader and check it for correct function with an ohm-meter. Like I said...I hope that's your problem. Check back to give us an update; ask more questions; etc...