Chevrolet Repair: 95 Astro Van, vacuum problem, actuator

Question
I have just purchased a 95 Astro van. The bi-level air does not work. It blows cold air but only out the heat and defrost vents. Is this most likely a vacuum problem or a control problem? I do have a control from a 94 van that I can try to switch out. Any advice would be appreciated.

Answer
it is a vacuum problem, but i don't know if it is at the control or the vent door.  under the dash you have vacuum operated doors, that deflect the air to the selected areas.  if it is not working, the vacuum doors may be stuck, the vacuum actuator may be bad, or the control itself may be bad.  listen for hissing.  if you have a spare control, and you know it is good, try that.  you can also remove the vacuum supply at the actuators and put in a vacuum guage.  then select that position and see if you are getting vacuum at the actuator.  if not the controller is bad, or the vacuum supply from the motor is broken.