this will be to do with the little flaps that move when the air position selector is moved on the dash i expect, the cable could have disconnected, does the dial/knob feel loose? work on feet? work at all when moved to head and windscreen/feet and windscreen? could need the dash out, can be a bit of a pain, well getting it together again can anyway! dont worry though its not going to be your matrix or anything serious in that sense, labour will be the biggest problem.
