NASC

Looks like I may have a stuck flap. Wherever I put the control the air goes to the screen, the rotary control now is harder to turn at the end of its travel. I suspec a cable problem but the garage tells me it is 6 hours labout to gain access. Is there anything I can check to confirm the cause before I splash out on 6 hours (or 12 hours doing it myself!)? Thanks all