97 Silverado 1500 A/C Weak

I have a a/c problem with my silverado. I turn it on high and I can hear the power of the engine but it doesn't seem to be kicking out strong air. Could there be something blocking the vents? It is not strong in any vents. I also have a tapping noise that seems to be coming from behind the glove box when I turn on the engine. It last for about 10 seconds and then goes away. This didn't hurt the heat in the winter, it blew great. Any help please? Thanks/

Terry