a/c question

I have 2003 Impala and the A/C will only work on the floorboard area, my question is, how do the baffles in the a/c duct work, are they vacuum controled or by solonoid, worn gear motor etc...I have no idea how they work to direct air to different areas in the car. But whatever it is they are stuck blowing air on the floor and not the vents in the dashboard, any help would be appreciated.