Your coolant temp may be getting too high and trips the AC on high pressure. If it was low on freon, it would shut off quickly at any temp.
It doesn't cost much to pull the charge, pressure test, and refill your AC. I would do that first, just to eliminate the guess work. Then, once you know your AC system is 100% properly charged and leak free, I would look at lowering your coolant temps by a few degrees
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