Air vent

The centre air vent on my mercedes will not
close is this an easy fix I can see a cap head inside has this anything to do with the closure or do I have to remove the air vent.
Also is the a/c on when the e/c button is pressed or is it off for MPG purposes what is the best settings. Thanks in advance Bobby.

1993 320CE 24V 75k miles

[J.HIDALGO]

If it is like my 86 300e, you can try to adjusting the screw behind the center screen. If that does not work, it is the vacuum actuator?.The entire dash has to come out. Been there, done that. If you have the manuals,have the time and patience you can do it yourself and save some money. Otherwise, take it to a mechanic. BTW, while you're at it, change all the vacuum actuators (total of 6 or 7, my had 7) so you do not have to do it again for the next 7 years ;^)
J.Hidalgo