If it is then, check the if the fan that "sucks" ambient air through the little screen next to the overhead light and control the flow of the AC may be malfunctioning. A easy and quick check is by putting a small piece of tissue right next to the screen. If it stays there, that is not your problem. If it does not stays there that is your problem.
Keep in mind it could be the the AC controller itself. Do alll the AC buttons work?
The way it is suppose to work is to start high and as the AC cools down the car the AC flow decreases.