....taking parts off my 73 450SL, words of wisdom would be welcomed from the venerable forum members. I have the old style heater control system, with two actuators on the starboard side of the firewall that operate the heater control valve. The heater controls will close the valve but won't open it. I open it by pushing on the rubber membrane thing, thus pushing the little rod that opens the valve itself. When I push either of the levers on the dash down, the valve closes. So, given that long monolog, do you think the guilty party is the valve control or a vacuum leak between the actuators and the valve control ( hoses and connections look good) or could the problem be with the actuators.
