Why does my car air conditioner blow in warm air?

I have a 98 Plymouth Breeze, bought used (cash car from dealer) in September. Now that it's getting hot out I need the AC and for some reason the air that blows in is warm, but when it's cool out the air come in cool. Yeah i know i should have checked out the AC before i bought it blah blah but i cant go back in time. Any help/info will be greatly appreciated. Also if there's a place that can fix it, please put a rough estimate of how much it'll be.