If you check voltage, it might be low. As voltage drops, the amperage has to increase to do the same work. That cause the breaker to trip. You might also see that the A/C isn't drawing too many amps when it restarts the compressor when it's hot. (the compressor, not the air temp) Have you noticed if the breaker is tripping when the compressor is coming on?
It also could be just a weak breaker, they do occasionally go bad.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI