1996 E320 AC Vents dont seem to respond well, airflow weak despite change in fan spd

[Machnumber2]

Hi,
I am kind of stuck on trying to figure out this problem and welcome any ideas.
I have a 1996 E320 Mercedes. On the ac control panel, when I adjust the fan speed to blow more air, the airflow doesnt seem to change very much even though you can hear the fan going faster. Also there is a button with 3 arrows I think, the up arrow I think means for air to blow up, the side arrow is for air to blow in the car and the bottom arrow for the airflow to be directed downwards. Changing the settings on this button seems to have little to no effect on the air coming into the car, especially with the vents that blow horizontally into the cab. I was wondering, what coud be causing this? Are there damplers controlled by acutators that control the airflow? Are they powered by vacuum and could there be a vacuum leak that is causing this problem? I do not notice any hissing sound when it runs.
Thanks in advance, I look forward to hearing any thoughts about his.