Ac only blowin out of floor and defrost vents?

It matters not what the specifics of the car is,....somewhere there is a vacuum problem with the air control panel. if it is electronic try switching modes many many times to different locations. If it is a manual(sliding bar control) same thing.... whip it back and forth quickly,.. see if that frees it up. With nothing else running except the engine get your ear up to the dash; you may hear a faint sucking or hissing sound. All cars are basically the same... It has a rotating disc with a plate of vacuum lines they may have gotten old, perhaps the seal on the disc is bad. Should be easy to fix yourself, but be careful with delicate vacuum lines.