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.

Check the MONO valve for having voltage to it as well as removing its lid and verifying the rubber diaphram within it is not torn. Do this with a cold engine, lifting the lid will only loose a small amount of coolant. Its located to the right just behind the battery looking from the front of the car. If torn buy a MONO valve repair kit. Loosen it from the firewall to access all four lid screws.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

Carnut...Thanks for the tip. I DID check the mono valve and it is shot. Than should take care of the heat issue with the A/C. The car also has some of the vacuum accuators on the heater/AC leaking. I'll address the mono valve first then the other issues. THANKS! Chris

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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.