A/C-Heater Control Panel: Defrost
WARNING: This page is about a different car, the 1996 Buick Park Avenue and 1996 Buick LeSabre. However, it is still accessible from the selected car via links, so may be relevant.
In this mode, outside air is pulled into system by blower. Air is cooled and dehumidified, then heated as necessary and forced out the windshield defroster outlets.