While no expert, it may be a low refridgerant charge. I know that too little charge will "cut-off" the compressor. If you have the correct manifold gauge set (134a or R12) you can check the system pressures when operating properly, and again when the system is inoperable. I cannot account as to why the system works for so long before failing, but I have seen systems that work for a few minutes and then cut out. Hope this helps.

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1992 500SEL 25K
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1995 SL600 120K
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