[Johnnyfry]

You are correct that having the 2AC breakers on opposite sides if the panel is a good idea, however it won't do much good if you are running on a 30 amp supply as it might not be sufficient to run both AC units even without much else running.

Another thought here is the fact that breakers have 2 trip out modes, magnetic and thermal. The magnetic mode operates when you have a short circuit and get a massive current flow and operates instantaneously. The thermal mode operates when you overload a circuit, say pulling 20 amps from a 15 amp breaker. It works by heat caused by current flow. That is why it takes several minutes to trip from a small overload and a shorter time for a larger load.

A poor connection on the breaker can also cause heat buildup and cause trip out, as can high temperature in the panel. My point here, (long winded as it is) is that having both AC units on a double mini-breaker as you do may cause trip out with the heat build up that occurs when both units are running. The breaker could also be too sensitive (faulty).

John