Oldsmobile/Buick Repair: A/C heater air flow, manifold vacuum, vacuum lines

Question
1998 olds 88LS 3.8l AT...with a/c or heat on ,the air flow only goes out the dash defrost and floor vents no matter where I set the selector switch.  a/c cools and heater heats. What could be the problem.

Answer
Hi
Check ALL vacuum lines from the intake manifold all the way to the HVAC controller inside car.
If you are getting good manifold vacuum at the controller, then It is MOST PROBABALLY the fault.
I hope this helps.
Follow post back, if needed.
Good Luck
Pawl