when i am accelerating or the engine is at higher rpms all of the air from vent or heat comes out of the defrost vents. if i let off the throttle it comes out of where it is supposed to. im guessing its some kind of vacuum leak. what do you think?

 

It is either a vacuum leak or rhe vacuum resevoir is defective,there is a check valve in it that can go bad.

 

which one is the vaccum resorvoir, the one from behind the bumper or the gray cylinder one?

 

Jesus H. Christ is there anything on a Cherokee that won't malfunction, snap, fall off, rust, breakdown or explode?

 

anyone know which resorvoir it is

 

The one behind the bumper. What is this "grey cylinder"??
The check valve is near the pass inner fender wall, close to the blower mot.

 

the grey one right by the tranny dipstick. at least mine is grey. it has a few vacuum hoses running to it. so the black bottle is the problem?

 

Ah, ok, that's the evaporative canister that caches the vapours coming from the tank and burns them in the engine.
It's either the black bottle or the lines.