A/C breaker trips

[John Churchill]

Well, I just got my generator started for the first time ever. Onan
7kW with a 20 amp and 30 amp breaker. When I turn on the forward A/C,
it runs for a while (a couple of minutes), then trips the 20 amp
breaker, even with everything else switched off. When the AC is off,
the breaker does not trip. I have only used shorepower on a 15 amp
circuit (with a long skinny cord to boot) and it trips that too,
although I am not sure that is a good test. The owner's manual says
that unit ought to draw 14 amps. I understand there is a much bigger
transient load as it cycles, but shouldn't it be able to handle that?
The rear A/C unit does not seem to run, so nothing to report there.
Any ideas of what to do or check? Thanks.