How do you easily repair the flap on a Ford Mustang air conditioner that is stuck in the defrost position?

That is all steel down there, check to make sure it is not rusted shut by moving the lever by hand, you can see it if you look under the dash on the passengers side.

The most likely problem is a broken cable, a new one is fairly cheap, but the easy fix is to buy the set from a classic mustang restoration outlet.

You can get the entire heater control bracket and replace it all at once for a little change.