Some more investigation is needed, preferrably by someon who is experienced with M-B HVAC systems.

The 'failure' mode, when there is no vacuum on acutator modules, is air will come out of the Defrost vents, and 'leak' from the side vents. So, a 'failed servo' should give you Defrost.

The floor vents are only used for Heating. They require a signal to the vacuum switch from the ACC panel, a good vacuum actuator, and good linkage to open the vent.

The center vents are only used in Cooling mode, not Heating, so they're harder to test in cold weather.

There are vacuum switches that actuate vacuum modules under the dash.

The vacuum switches are accessible by removing the right side of the console, and the actuators are behind the radio and switch panel, which must come off for access.

Good diagnosis first, with vacuum gage and in the right sequence, will tell which actuator(s) might be leaking, before removing panels and other equipment.

Best Regards
Jim