I have a 1985 300D turbo. The 2 A/C vents in the middle of the dash don't work.Are they vacuum asssisted? Can somebody tell me how do fix this to get air to disperse correctly from all 4 vents? The outer vents work fine.It is as if the middle 2 are plugged.

Yes, the center vent door has a vacuum actuator that pulls the door open.

Either loss of vacuum or electrical malfunction of pushbutton OR switch-over valve.

Do you have a vacuum guage to check for vacuum?

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Or the plastic pin that secures the actuator linkage to the flap broke.

For a quick fix, just take out the glove compartment, you will be able to see behind the vents then, and will be able to see the actuator that controls them. Simply wire the vents open. You can always use the vents themselves to open and close the airflow. Make sure to cap off the vac line to the actuator or you will have a leak... which will effect all kinds of stuff including how the car shifts. Best way I've found is to remove the AC controls, and access the Vac block, then pull the vac hose off and put a vac cap in it's place. the lines are color coded so it's easy to see the right one. This is also a good time to get out the mighty vac, and test all the other pods and cap or replace as needed.