windscreen heater/blower vents

I've got an issue with my mk2 Golf 8v where only the middle 2 vents on
the dash that demist the windscreen work. I've looked at a few scrapped
golfs in the dash and there is only 1 feed to all 4 vents so does
anyone know why the left and right vents don't have any air coming out?

I can't quite see how to get into there to see what the problem is
short of removing the dash which i'm not exactly fond of trying to do
as this is my daily drive.



Any ideas?



cheers

 

Probably the flaps in the heater box that switch the air from top to bottom

 

Why would 2 of the vents still work though? When on setting 3 they middle vents are quite strong so enough air is getting there.