Actually, the photo above is off of Ebay. My car does not have Cruise Control.Couple of things here. First, the vacuum tank shown in the diagram is actually a globe or spherical plastic ball. The picture doesn't portray it all that well but if you look closely you can see the mounting tab peeking out from under the two air nipples shown.
Secondly, the picture you posted is, unless I am totally mistaken, which does happen at least once a minute, the actuator for a cruise control. On the motor, it is attached to a "Y" shaped bracket that bolts to one of the drilled and tapped 3/8ths NC holes located in the driver's side head and between it and the firewall. In the picture you can see the two mounting studs that attach it to the arms of the Y. The flat slide arm that protrudes from in between the studs is attached to a diaphragm that is inside the flying saucer shaped metal body. On the motor,. there is a short chain that runs from the end of the slide to a pivot point on the throttle lever on the carb or TBI.
As for your air flow issue, the diagram shows the upper and lower mode valves and, just a thought here, it could be one of them that has malfunctioned. There is also a flapper panel in the ducting that is mechanically adjusted by means of a lever/cable mechanism that is part of the control head. Using the lever to move the panel modifies the air flow from down low to the upper vents. On the control body it might show as a horizontal slot with a small knob sticking out of it. Sometimes the actuator cables jam or break.
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