1996 Chevy s10 air circulation problem?

I have a 1996 Chevy s10 pickup. 2.2L 4cyl engine. The air conditioner works just fine, and blows cold air. My problems is that it doesn't flow out of the vents on the dash board. It blows out of the top vent by the windshield and the bottom near the pedals. We replaced the vacuum line to the vacuum canister and it didn't help anything.