This should answer your question. I too had this same problem on my 96 mustang and found this site useful. http://forums.stangnet.com/740776-posessed-air-conditioning.html
most vehicles use a vacuum diaphragm to move the mode door inside the dash from the floor to the vents to the windshield. Either the vacuum diaphragm is leaking or the vacuum hose has become disconnected. In my 85 topaz the door pannel vents are used to defrost the side windows.
it strides
by walking
by using its wheels and gas
the problem is when the baffles move from heat to ac and vent to defrost they either get stuck or the controllerr is bo. this system is built to fail safe in the defrost mode. Thus ac comes from Defrost vents. Apparently it is wide spred with Ford and Chev. As it is in my 2001 Ford F-350, My opinion To much Matel Toy company plastic and cheep parts we pay considerable money for from the dealers. 1) check your controller at the dash probably vacume 2) check the acutator at the butterfly flapper. Some vehicles are easier than others.....
Move the heat control lever to the off position.
almost all the time that's why they call them mustangs
If you are refering to the vents near or on the door try toggling the switches near the steering wheel. One is marked L and the other R. You can move them up or down.
There is a motor that controlles the swiching door above the gas peddal and slightly toward the passenger side. It could be the motor or the door itself. You can test this by switching the controlls from vent to defrost. if you can see the cables and gears on the motor move, more than likely you have a problem with the door. If not you will need a 7mm socket to remove the motor. This motor is a dealer only item.
almost all the time that's why they call them mustangs
Did you happen to move it to Defrost when you turned it off? The ac compressor also runs in the defrost cycle to keep the seals lubricated during the winter months when the ac is not used.
You have to take out the heater vents to be able to move the console forward.