Trailer AC works plugged into house plug but trips breaker on generator and a light plant why??

When you say "power box" do you mean the main breaker box in your house? Is the generator hooked up to the breaker that you say trips when the generator is on? There is a short somewhere. First check the generator. Is it running OK. In other words if you plug something into the generator receptacle directly, does it work? If the generator itself works properly, then check the wiring from the generator to the circuit breaker. DO NOT use the generator until the problem solved = safety first.

if no power on the plugs check for the cercuit breaker fuses and check for your load why it is tripping the circuit breaker the unit sbould not be overloaded

What size circuit breaker is on the generator that is tripping? You'll need a 20amp for AC alone, then consider other things that are drawing current when RV plugged in like , converter, fridge etc that may be drawing current at same time. Make sure fridge is on propane, as well as water heater if you have electric element option on water heater. AC may only draw 12-15 amps when running if good and clean and wired properly, but will draw 17-18 amps when compressor kicks in. Perhaps generator not designed for that surge?

Unit may pull as much as 17-18amps when compressor starts up, but level out to 12-15 amps when up and running. Keeping in mind that is all relative to proper 120v incoming voltage, heavy enough wire to run the application etc. If your AC unit needs cleaning , it may draw an extra amp or 2 . With that said, when your at the park, first thing I'd question is their incoming voltage to RV, and try running fridge etc and anything else on propane if possible. The AC alone should not cause 30amp at source breaker to trip, before 15 0r 20 amp breaker in RV that is connected to AC trips. If it doesn't trip your breaker at home, and all is connected same at park, then I certainly would suspect bad breaker or voltage/wiring at park is the cause. P.S. I noticed you said you have 12 gauge wire (rated at 20 amps) connected to a 20amp breaker at panel, but RV is plugged in to a 15amp receptacle, I will assume with a 15 amp adapter from 30 amp plug. Do you see any hazard regarding 15 amp rating on receptacle? ( just a little advice.)

Where do you have it plugged in to? Is it plugged in with 30amp plug to receptacle. Which breaker is tripping, the one for AC only, or the main breaker for trailer, or breaker at plug in?

Because it won't be powering just your AC, I would recommend 5000W. It's that big amp draw when compressor kicks in that will pull it way down, if not strong enough. Take for example the fact that a dedicated 20 amp breaker and cable are the norm for RV's to use for AC now. Double check also that the generator your purchasing will take a momentary surge draw of up to 20+ amps without tripping breaker on generator. I say 20+ because once RV is plugged in or wired to generator, it will be powering any other hydro operated appliances, lights, converter etc that the trailer has on board. I bought a cheapie rated at 4000W, and 3000 running watts, but it kicks out the breaker just trying to start my portable air compressor, rated at 15 amps.

What about when you have it powering the motorhome, without AC on, does it trip then? Do you have anyone you know with a multimeter and knows how to use it? How about buying a plug in voltage meter at a hardware store as a good start. You simply plug it in to a receptacle in your motorhome and it will tell you the incoming voltage and they are not very expensive. That will help diagnose generator problem.

I take it you have RV plugged into generator. Hopefully direct with no extension cords. Are you using a 30 to 15 amp adapter to plug into generator? What is the rating of the breaker on the generator that keeps tripping, suspect it's only 15 amp?

You need an electrician be careful

try to plug it in another circuit of ur house.. to see what happen