I'm going out on a limb and guessing the AC is not brand new either?
All AC systems eventually leak. Most are OK for 10 years or so and by 20 they've lost
some gas. When that happens the compressor
has to work harder and longer and then it draws more current, which is all you need to pop the breaker.
So, given that the breaker is OK until the AC has been running for a while, you might also want to put an ammeter on the AC circuit alone, and see how much that is drawing compared to the rating plate that is on the compressor
. If the compressor says 15 amps but you see it is drawing 20...or even 17 during runs...you know you've got an AC problem. That might be the only problem, or just a coincidental problem, but it is worth checking out.
I'm also told there are two kinds of circuit breakers: The common cheap
"thermal" breakers, where too much current causes them to overheat and trip, and a more expensive "magnetic" or "magnetodynamic" type, which throw when the increased current causes a higher magnetic field in the breaker. The magnetic type supposedly are way more expensive but last much longer. The thermal type have a definite number of trips in their life cycle, and then they need to be replaced.