I know we are discussing completely different boats here, but on Adagio (SM209) a few years back I had a terrible time finding and solving an intermittent fault in our Climma system. I am not sure exactly which units the A55 might have on board, but if the breaker will not reset (in our case is was the Main Breaker for the whole boat) it is likely due to a ground fault that allows one (most likely the neutral) side of the power circuit to bridge to ground. It doesn't take much at all to trip those current sensing breakers (again, in our case .05A) so it could be anywhere along the system pathway. The ultimate cause was a blockage in the condensate water pathway which caused the drip-tray to fill up and water to touch the connector to the heater coil (remember that SM folks! FWD AC tubing needs to be kept cleared :) )
If I were to start troubleshooting again, I'd first try to isolate which of the units is faulting (do A55s have three as in SMs?). This would mean disconnecting shore power and then un-wiring (I presume there must be a connector/clip going to the units) all of them to prove that the fault is indeed in one of them. If you can isolate which unit is causing the fault it makes it a lot easier to press on.
I'm not going to venture any further suggestions as I simply don't know the 55.