I have an odd problem and I have a feeling someone on here can point me in the right direction. My AC blows pretty cold, but with the AC on the car seriously drags ass. The second I turn it off my acceleration improves very dramatically and vice versa. In addition to this, on long drives or in heavy traffic the engine gets very warm with the AC on (110). Ive already flushed the radiator, changed the thermostat and checked the fan clutch. I dont know where next to check. Is it perhaps the drive belt being too tight?

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1983 300SD White with Grey interior