Adjusting motor Circulation air/Fresh air defective??

Hello!

Got a problem with my 96 A8 with automatic climate control:

I have the feeling that "cleaning" of fogged windshield etc. It takes a very long time, or it only runs unsatisfactoryly.

Now I fear that the actuator for circulating air/fresh air could be defective?!

How do I get this??

When I switch from circulating air to fresh air, or vice versa, I hear a slight buzz somewhere.

When I pull off the ignition I hear this buzzing again, however, I think with a couple interrupting, or is that normal???

Welcome

Henning