Start w/ the basics. Is the compressor turning? Look at it. The pulley always turns w/ the belt. The compressor turns when the outer section of the clutch turns once the clutch is engaged. If not turning, you sure won't get any cooling. If turning, is the suction line getting cold. If so, perhaps your heater is on and over-powering the AC. That is a common problem in W123 cars. When not moving, the AC doesn't cool very well. That is very noticeable in my 2002 T&C as well. I verified that the electric condenser fan turns on in both vehicles, but that doesn't cool it near as well as the air-flow when the vehicle is moving.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans