ac/heater climate control / floor vent only

The ac and heat only come out the floor vent and the small window vent, although I
can still can turn the button to change to other vents. the blower moter is fine but its really difficult to defrost the ice inside and out in the winter time. I was thinking if I replaced the whole unit (ac/heater control unit) with a used one then maybe it would work again for all the vents. Has any one tried this or know of an inexpensive way to fix this? THANKS

my sebring would not go to vent it was the vent motor calibration had to unhook the batt for 15 min when you rehook it will go to def then vent to cal itself