On my new-to-me 2001 Carver 530, my master stateroom air conditioning doesn't work. Salon, VIP, and Pilothouse Marine Air units are working great but the breaker to the master unit blows instantly. I've replaced the breaker assuming that had gone bad, but same result. I've checked, cleaned, and reinstalled ground on the unit. I've removed the ducts and reached inside and the cage spins freely. I cleaned all the grounds on the small buss bar in front of the port motor. Same result. Breaker flips immediately. Short in the motor? I'm at a loss. Any help in tracking down the culprit would be greatly appreciated!!!