The air direction is controlled by vacuum actuators and needs vacuum from the engine and a vacuum reservoir to hold vacuum just for this reason. Lets start with making sure we have a reservoir that can hold vacuum. You can use a hand vacuum pump or put it under water and see if air bubbles come from a crack. The reservoir is behind the battery mounted to the evaporator housing under the hood.
Lets start here
Make sure the hoses and vacuum lines are good too.
Thanks for getting back to me. Your answer sounds fine, but I am unclear as to the location and indentifacation of the reservoir and vacuum actuators. Is there any chance you can forward an automotive diagram that would indentify these areas you mentioned?
Hard to get info even from dealer on vehicles older than 10 years. The pictures that I can see are not great. The procedure states to remove the evaporator housing(under the hood) to get to the reservoir. On newer vans they changed the location. The vacuum line that gives the a/c system vacuum is usually black and goes through the firewall. They also usually feed the line through near the heater core, in this case passenger side of the vehicle.
I found a GM style vacuum reservoir for 15$ at autozone