I have a 97' Ford Mustang. Recently, my a/c stopped blowing out of my "vents".?

It still blows out of my "defroster". I can turn it to whatever, a/c defrost, feet, anything..It all goes to defroster and blows out there.My question is, what is making it do that? What do I need to do? Did my something under my dash fall or something?I live in Florida and its super hott!!! Someone please help!!I need my cold a/c blowing RIGHT again!!