Ford Repair Questions? Ask a Mechanic for Answers ASAP
Check for a stuck heater control valve. This valve is shut when the A/C is in the MAX position and open at all other positions. The best way to test it is to remove it from the heater hose and visually look at it to see if it is open or install a temporary flush tee to by-pass it altogether. If the heat comes back then you know the valve is not switching like it should.
Have you looked at that valve yet?