The AC is blowing cold by the windshield but not blowing out dash vents why

Is this repair expensive? Is it something that I can do? Or will it have to be taken go the dealership? They want $100.00 just to diagnose the problem Thanks, Jamie

This is something you can do.....Follow the vacuum line through the firewall into the engine compartment all the way. The line in the engine compartment is the most likely location for a cut or break in the line.