Generator can only run AC with everything else off

I found the owners manual for your generator. Based on the wiring diagram it looks like each "hot leg" when used with 240 volts is protected by a 13.5 amp breaker. That will limit each to that. Your AC is only a 120 volt appliance, so it is only using a single "leg". Therefore, you can only use 13.5 amps. If you can connect with a 120 volt connection instead that would likely solve the problem.