A/C Heater air flow

[gbratcher]

On my 99 montana the air flow doesn't change when the position selector knob is moved to a different position. Most of the air comes out of the floor vents, but a small amount comes out of the upper vents. I have checked the vacuum lines in the engine compartment & they are good. Does anyone have any ideas what My problem could be & how to fix it? Thanks

[Tech II]

Go under the dash on the passenger side and find the vac source line....with the car running, does it have vacuum? It is usually purple or black in color....