It's best not to supply 120v to the converter without batteries (even defective ones) hooked up. The converters put out a choppy voltage that averages about 13.5 volts and the batteries act as a filter to smooth out this voltage. Running the converter without the batteries may damage circuit boards in the refrigerator, tank monitors, radios, etc.
You should be able to unplug or turn off the breaker for the converter and still have air conditioning and AC outlets active if you are doing work on the coach.
John W. Irwin
2018 Interstate GT, "Sabre-Dog V"