While I have experienced what Jim said about the A/C cutting out util the car is restarted I have also encountered times when it came back on its own in a few minutes. A new tensioner took care of my problem. Don't rule out belt slippage just yet...

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)