Auto Air Conditioning & Heater Repair: Buick A/C vents, buick park avenue, climate control system

Question
My mother's 1996 Buick Park Avenue w/ 120,000 miles has the fully automatic climate control system.  Lately, the vent doors for the middle (dash level) a/c remain closed when a/c is really needed.  No work has been done on the car, except oil changes, in several years.  i took the car to a local mechanic and he said 'take it to the dealer'.  i want to sell the car, but won't get much if a/c doesn't work.  is this likely to be an expensive fix?

Answer
The most common fault is a vacuum leak in the small black plastic hose that comes from the engine compartment thru the firewall an in under the dash.

Look for the vacuum line going thru the firewall and back track it into the engine compartment and you will most likely find it broken or split somewhere in the engine compartment.

Find a connection and put a vacuum gage on it, You should have full manifold vacuum.