Super Moderator UK 2002 SLK320 Blue
On mine the demist button in the centre is the rear screen heater demist. To defrost the front window I turn my right hand knob to 3 o'clock (IIRC) to put the flaps into a defrost position and then turn the fan up high with the left knob. If there's any actuator in the dashboard it is controlled by the turning the right hand knob and therefore the spigots where they enter the control unit.After studying the backs of both dials on then I have come to the conclusion that the demist 'flaps' that operate by an electrical signal that allegedly operates rods or a single rod must be where to lack of airflow lies !!
What then do the two white spigots do other than direct vents/flaps for the other functions of directing the air flow that the fan speed creates onto the parts of the body/interior as directed on the dial.