1996 Ford Windstar Air conditioning is a little off kilter.

The switch could be bad. However, it sounds like a vacuum leak to me. THe vent doors are actuated by vacuum. If there isn't enough for it to change, it won't. As far as the heat to the rear and only on the floor, check the blend door for proper operation and again vaccuum leaks for operation between floor and overhead.

Check both under the dash and the hood for vacuum leaks. If you are lucky, you will hear a hissing sound where the leak is with the engine running.