I have just had a bit of trouble with the heater in my T2, which was due to a loose cable on the temperature control knob. Now fixed, but that's another story.
However when I was trying to determine the cause of the problem I noticed that the knob that controls the airflow also operates a cable. It is possible that the cable on yours has come adrift.
I would suggest that you have a look bin the footwell to see if the linkages are all moving. They are quite easy to see and you can gently move them by hand if necessary. (they are cam shaped plastic parts moved by stiff wire). If they don't move when the control knob is turned then I suspect it's a cable.
Worth a look and no tools required.
Regards
Alan