'92 TA AC/Heater control.
 

The cold and hot air will only blow through the defrost vents and foot well vents. The only exception is when you cycle through the options and back to "OFF" and then to "Max" it will blow out the center dash vents. The disk in the back of the control that regulates the vacuum sounds like it is leaking. Has anyone else been through this that can offer some insight?

Thank you