A/C Control Levers

[athflying79]

I have a 91 535i. The A/C slide levers all work great except for the very top one that controls the upper (windshield) vents. I thought maybe the cable was binding up, but I took the glove box and trim panels out, and it's the actual lever that goes to the A/C distribution box. The cable is fine, but something internally isn't moving.

Any ideas how to fix it.

[athflying79]

Are the internal flaps accessible without removing nearly the entire system?? I've looked all over the net and haven't found any good answers and the Bentley doesn't have to much detailed info on the subject.