You don't say what kind or age of coach or type of electrical service (30 or 50A). Could be a number of issues. If you have 30A service, there is almost certainly some type of energy management system. Our Bounder had 30A "shore" power but 50A generator service. It was a weird setup. When hooked up to shore power, it used an energy management system to alternate A/C's and shed certain loads but everything would run off the generator. If your coach has an energy management system, that would be a likely place to start looking.
There are a number of possible answers.
- Internal generator issue
- Breakers on generator
- Transfer Switch
- Energy management system
- Disconnected/broken wire between any of the above
Since it works fine on shore power, it wouldn't be the breaker in the load center. The only "quick" checks would be breakers on the generator as others have suggested. Beyond that, its going to take some methodical troubleshooting. If you're comfortable using a volt meter, you can start tracing power from the generator to the transfer switch.
