A/C Overloading My Generator

That really is a big load for a 3K gen. Think about it; that's only 1300~1500 watts for each and that includes the high demand of starting them. You need to be able to start one without the other trying to do so at the same time.

As others have pointed out, the DC converter depending on what unit you have can draw enough power to trip a 2000 watt generator when the batteries are low. You can turn it off by tripping the circuit breaker, or pulling the plug etc. The water heater as mentioned can be a large draw as well. I'm missed the water heater switch setting and tripped my generator when trying to run AC more than once.

As already mentioned, without a good starting capacitor, even a 13.5k ac can trip a 3000 watt generator. I too have installed the Supco hard start caps in my last couple rigs. They are reasonably priced and seem to hold up well.

Finally, are you taking your Handi out of ECO mode prior to turning on the AC? Most of the friends I camp with that have the Handi find it won't run the AC in ECO at the altitudes we camp at. Not sure how they work at sea level.

Hope you get it sorted out

Are you at a high elevation? Generators loose power capability as the elevation changes. A generator that is marginally big enough at sea level won't be big enough in the mountains.

Like bgum writes in his above post the converter may be charging a depleted battery that's taking quite a few amps. Often times I have to unplug my converter to run the AC from my Yamaha 2400.

Is your water heater on gas or electric? Is your converter trying to charge your batteries?

Your a/c unit is likely missing it's starting capacitor. The factory leaves them out for some reason.

Supco has basic capacitor kits... There's much more expensive versions out there as well.

Sounds like your doing everything right by eliminating all other power drains. If there is any way to try turning the AC fan on low , then set your ac to come on maybe that would allow it to step in rather than the fan and ac at same time.
If the generator is brand new it may be defective if it wont run a 13500 AC.