Eureka !!
I've found the problem! The hot wire to a water heater was patched into the same circuit breaker as the a/c. Heater operated normally on both shore power and generator. When I removed it from the breaker, the generator operated the a/c without a problem. Now I just need to determine whether the heater itself, or the wiring leading to it, is defective.
Thanks to everyone who shared their ideas !
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