Climate control issues

I got this car from my aunt. It sat for a year, due to this the battery drained and I replaced it. The air conditioning works wonders and blows out really cold air. The heat also works. But when I try to select a different vent selection (other then head/front) the led light changes to the right button, but air continues to blow out the head/main vents. I usually would not care, but I need to have air go through the defroster vents. What could cause this?