On my 1980 300D when I press the a/c control switches no air comes through the vents except when I press the defrost button. What does this mean? And another thing is it possible to upgrade to the newer style a/c switches that come on the 81,82,83,or 84 300D modles? If so is it easy ? do they just plug right in?

Not knowing if you have a proper charge in your A/C system, you probably have a bad climate control servo valve. It is located on the passenger side engine compartment. It has a BUNCH of vacuum lines and a few heater hose lines to it.

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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.