Merc is a 1986 560SEL USversion.

I have diagnosed my "cold feet" problem to the fact that the heater door does not retract once the defrost closes is. In other words-- if i push leftmost defrost switch the heater flap door closes properly directing all heat to the windows-- when i hit normal heat button the flap door does not retract at all. The pass side works fine.

My question is for those experienced here are what are the next things to check here and how can i possibly get to the flap control actuator. I have looked and looked and cant see the control.

Thanks