a/c unit

Need more information. What size A/C units, what size is the generator, and what else is on when trying to turn on a/c?
RV information may also help.

Probably the least expensive attempts to fix the situation are replacing/add a start capacitor. If the unit doesn't have a start capacitor, or if the one currently installed has degraded, adding one may take enough load off the generator to prevent it from becoming overloaded and shutting off during A/C start-up.

Probably the start cap. A visual inspection of it would show if it's bad.

are you sure the gen will handle 2 ac's?Does the ac run on shore power?
Its been awhile since I worked on these small ac's but lean towards a bad "run" capacitor as this must be good to START.

Happens to ours. Discovered genny not powerful enough to support the extra draw on its power when A/C tries to power up.