I posted in the Diesel section but got no response. I am working on a 1983 300DT wagon. I cannot figure out why when the A/C is running, I get cold air from the left vent by the door and HEATED air on the right vent by the door. I replaced the temp controler with a known good unit. NO HELP. I then replaced the push button assy with a known good unit. No help. I checked the operation of the 5 solenoid vacuum valves behind the 4 switches on the console and they are all working. I know that Mercedes uses a split heater core but on the later climate control('81- later), It isn't used as a split core. Is there anything that I am missing??? I keep coming back to the car with new ideas and they are not working.

I have a good mechanical knowledge of these cars but this one is stumping me!

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.