I found the following two posts on car forums when I looked for an answer to the same question (95 mustang blows only through defroster). I haven't tested this yet, but the two answers did come from different boards. It is a vacuum supply problem. Look closely where the vacuum tree is on the plenum. Ford uses a rubber fitting with plastic line, the plastic line usually cracks at the rubber fitting. for the a/c prob. check the vacuum line going through the firewall by the passenger side engine compartment. if that line breaks (and it does) you wil only have defrost vents working.
Transmission Modulator 1996 ford mustang can not find location
( bulb # 168 ) for a 1996 Ford Mustang license plate light
Yes, it will.
The 1996 Ford Mustang GT was rated at 215 horsepower
How to remover 1996 ford mustang radiator fan from the radiator motor
The 1996 Ford Mustang GT was rated at 215 horsepower
Yes, these tail lights are interchangeable.
Yes it certainly can.
If it's stuck on defrost, the problem is most likely a small vacuum line near the rear of the engine by the firewall. Mine broke right at a junction.
take it to a mechanic
Not directly, no.
There is no 5.0 engine in a 1996 mustang. 96 is the first year of the 4.6 engine.