Coming on for 3-5 secs, and then needing a restart to do the same again means either the compressor is not turning at the same rpm as the engine, i.e. you have a loose or a slipping belt OR your compressor's speed sensor is faulty OR your engine speed signal is not reaching the Klima relay. The speed sensor signals can be tested. Does your car have a Klima relay similar to what I have on my 87, 260E ? If yes, then check this post, I have posted a step by step method to check the compressor cut off.

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Saumil S. Patel