Last week my center dash cooling vents stopped opening. I pulled the Vacuum line off the electrical vacuum control for the center vents and applied vacuum with my hand tester. The vents open and stay open with vacuum applied so I'm sure the Vacuum servo is OK. I measured the voltage on the connector to the electrical vacuum switcher and found it had + 12 VCD across the 2 pins except when in defrost mode. I checked to see if any vacuum was present on the output connection from the switcher where the hose goes to the Vacuum servo. No vacuum So I suspect I have a bad electrical control valve for the center vents. However I wonder if the Pushbutton unit might actually be the culprit. Part of this reasoning comes from the fact that during cold weather when heat is called for the foot vents do not open. however if I put the system into bi-level mode the foot vents open in both heating and cooling modes with out failure. Does Anyone have a schematic diagram of the Pushbutton unit so I can figure out if the PBU is flakey or I simply have a bad Electrical vacuum switch.

Thanks Russ