Air Conditioner Blower Volume

I have a 1997 Chevrolet C-2500 with 171000 miles. The blower does not seem to be blowing very hard even on max output. When you take it off of max, it is barely putting any air out at all. The voltage and everythings checks out fine. I have read your replies about the "doors" not opening all the way. Exactly how do I find this out?

Thanks