The access door under the fridge is probably the power center; if you open the metal cover (often there's a sort of twist latch that you need to use a flathead screwdriver or similar flat thing to turn) you should see the 120V circuit breakers and 12V fuses for the house part of the motorhome. Often the converter is also part of the power center. Depending on the model of the converter, it may hum or make fan noises when it's in operation--that is, when connected to 120V shore power or when running the generator.