A/C on shore power trips breaker after 30 minustes

I just looked at the circuit breaker and the one that trips is 20 amp and next to it is a 30 amp breaker. The tags on the power door say the 30 amp should be for the A/C and the 20 Amp for the Microwave. Maybe that is the problem? What is weird is we have never changed anything with the electrical panel and have had this unit since 2010. Could it have really been wired wrong and now decides to fail? Does the Microwave only need 20 amps?