Why my 1996 buick century car air conditioner blows vent air only?

it's a buick 1996 Century with a 3.1 engine. I've checked the freon and it's find and I've ckecked the switch and it's find also.|||You have a vacuum leak in ventillation system . THe vacuum is used to open and close your vents from defrost to vent to floor ect|||Try to re-gas the aircon. My 2000 Golf iv did the same thing|||I would check the conection under the dash sometomes they come loose or the vent doors get stuck.|||CHECK THE LOW SIDE PRESSURE SWITCH THAT IS ON THE ACCUMULATOR.