AC vents reacting to throttle? Where do I start?
 

Whenever I apply my throttle more than halfway, my AC vents partially close and divert to my windshield defrost vents. If I take my foot completely off the throttle, the vents correct themselves (no defrost...) within a few seconds.

So it's clearly a vacuum related issue, but how on earth do I go about repairing this?? If all vacuum is released from the vent flap system, is it the "default" position to have the defrost flaps full open? Should I just cap off the vac line until winter comes and I need defrost again?


'85 W123 300D BTW...