I have a 1975 450 SL that keeps us plenty warm. The heater won't shut off with the temp control levers for the drivers or passenger side. Upon following the levers I find that they connect to a rod on each side which has rods connecting to a top and bottom damper which I presume when the dampers are closed they will turn off the water valve to the heater. When I get under the dash and try to move the rods by hand I hear one hitting something so it appears something has it jamed open. I took the insturment panel out to replace the ignition switch and could get to the top rod that connects to that damper. I took the top rod loose and the top damper is free. I then reached under the dash and could not get the bottom damper to move very much until I heard the clunck again. Does anyone have an idea what I am trying to say and/or how get to that bottom damper and see what is keeping it from closing. This past summer I just closed the vacuum water valve and sealed the vacuum hose to keep it closed. I could continue to do it this way however I would like to have a little more control than full heat or no heat.
Thanks
Doug