I'm assuming the air conditioner works correctly when plugged into a 30 amp or 50 amp pedestal. But if this is the first time using the AC, you might just have a problem with the AC unit.
With the on-board generator, there's a transfer switch that has an input from shore power and another input from the generator. The output goes to the circuit breakers. Usually the generator has priority; that is, if you fire up the generator, after about 30 seconds, the transfer switch routes generator power to the circuit breaker panel, and breaks the connection from shore power.
Leave the air conditioner circuit breaker OFF and start the generator. Then use a volt meter to check voltage at several outlets around the RV. Check the microwave outlet among others. You should see 120V between hot and neutral, and also between hot and ground. You should read 0 V between neutral and ground. If you're not getting these readings, you may have a problem on the generator side of the transfer switch, or back at the junction box where the generator is connected.