HVAC air distribution problem

have a 1998 jeep cherokee with six cyl engine..sometimes when in driving on the highway about 60-65 mph the ac suddenly comes out of the defrost vent then i lift the gas pedal and it goes bk to normal on the ac vents..what could b happenin..any suggestions would help....thanks!

Vacuum leak in the HVAC system. Could be a faulty check valve or leak in the reservoir, or a vacuum line is leaking somewhere between the source, (intake manifold) and the actuators in the dash.

Concoured with vacuum leak.

yep definetly a vacuum problem with the lines or the canister itself

Look by the battery,the plastic vacuum line gets melted by the battery acid