The air not coming out of vents but it's turned on and blowing
Check the ductwork behind the dash (easier said then done) sounds like one of the ducts has come unhooked. HTH. -Jim
Check the vaccuum lines as well. The main one should run over the right wheel well in the engine compartment. It goes to a block behind the glovebox where it splits off into 4 colored lines that go to the diaphrams that contol your vent doors. It's tedious but much cheaper that having diagnostics run on the system. I use a small piece of paper to check for vaccuum because it's so little it's hard to feel with your finger.
Looking for a Used Grand Prix in your area?
CarGurus has 2,643 nationwide Grand Prix listings starting at $950.
Search Pontiac Grand Prix Questions
Pontiac Grand Prix Experts