air conditioning question

Hello, i am new to naxja. I have a 1998 cherokee sport, when i run the a/c and i have it on vent it automatically changes from vent and comes out the defroster vent, other than that a/c works great. hopefully you guys can shed some light and send me in the right direction.

There should be a vacuum canister passenger side right behind the bumper. Check that for cracks and checn the line for cracks/damage as well. Typically when the HVAC system defaults to defrost there is an issue with the vacuum reservoir or associated lines.