climatronic problem, other common faults

[ben10]

hi there, my wife and i are looking to buy a mk6 passat tdi 105. we have looked at a couple over the weekend and found one we like, however there is one small issue, the climatronic only works on blower speed 4, nothing happens on 1,2,or 3 could anyone shed any light on this? is it a simple fix or is a new climatronic unit needed? also are there any other common problems/issues to look for when buying a used passat? the model we are looking at is an '06 1.9 tdi 105 with a manual box. many thanks in advance to any advice provided, cheers