My girlfriend has purchased a used 1993 Buick Regal which has a dual pushbutton climate control system. Everything seems to function on this pushbutton panel accept that the air is always going out the defrost vent and the floor vent. I cannot get it to switch to anything else. I know that this system has a vacuum control module under the dash that controls the dampers. I can see that some of the vacuum actuators are trying to work but they do not move far enough to make the dampers move. Does anyone have ideas on how to troubleshoot this vacuum system. Weak vacuum? Where is the source of vacuum? Troubleshooting tips?....Please help!

i know that when i worked for dodge, they had something called a "blend door actuator" and that is what helps aim the air...i am sure that it is a similar issue.