Running 2 A/Cs on 30A is marginal unless they are smaller A/Cs. Typically this is where the 5500 shines as it should have one A/C on 30A and the second A/C on the 20A CB. Check to see it there are any other loads on the 20A CB.
There are a variety of reasons for the tripping CB. Dirt on areas inside and outside, weak CB, hard start capacitor failed or not installed, A/C problems and gen problems.
Rigs with this gen can be set up to run only one A/C at a time when on 30A shore power, ie they may automatically switch A/Cs but only one will run at a time.