[satz]

OP, do you use AC on recirc mode continuously?

On my previous car (VW GTI) that did exactly the same as you describe, I used an AC cleaner spray (i think from Wurth). Removed the pollen filter, and sprayed it into the AC intake while it was running. Let it run for a few minutes.

That way it cleans all along the AC intake passages. Also look into the AC intake and see if you can see small particles of leaves, etc and clean them out with a vacuum cleaner (before you spray).

If all that doesn't help, you could have mould build up on your evaporator. In which case professional AC repair place may need to somehow clean the evaporator.

let us know how you go