heater problem on 2001 C230k coupe

[discoking]

My brother has a C230k coupe and has a problem with the heating.No matter what temperature you want it only blows hot and it only blows out of side vents and screen demist vents.After the the car has warmed up a bit you can get a teeny trickle of cold air from the middle face vents but it's hardly noticable.

The control unit is the non digital manual one if that helps any.

Any ideas?

 

[turbopete]

sounds like the duovalve has stuck (or whatever it does) as they always blow hot when they go wrong!