CHEVROLET ASTRO DEFROSTER

My Heat And Ac Work Just Fine But The Air/heat Doesnt Come Out Thru The Front Vents Only The Defrost Section

My Ac Is Only Blows Thru The Defrost And Cant Set To Front Vent

When Running The Heater/ac The Selector Switch Will Not Change The Air Position. It Stays On "floor/defrost At All Times. It Started Doing...