ac/heat won't switch modes, blows through all vents?

I have a 99 Olds Intrigue with climate control. I have removed part of my dash to find none of the vent dampers, located inside the ducts, move. When I switch modes on the controller I can hear a switch like sound coming from the vacuum control solenoid, but no air pressure to open and close the vent dampers. Could it be the elecronic vacuum control solenoid? Is their some kind of compressor which pressurizes the vacuum lines? I have checked all the vacuum lines for leaks. If I manually close/open the dampers, I can hear the air movement through the vacuum lines, so I know nothing is plugged.
Any related experience or help would be great, thanks.

Eric

Which engine do you have....SII 3800 or 3.5L?

In any case are you sure the accessory vacuum for HVAC from the intake system is good?

Sorry, I meant to edit my thread to add 3.5, but the server must have been busy yesterday.
I checked the vacuum and did find a piece missing on the vacuum line in the engine compartment next to the battery. funny that GM would run it under the battery tray. the exposed vacuum line is dry and brittle and cracked. used some electrical tape and it now works great.
thanks, Eric