On my 9 hp onan genset it runs fine but the 20 amp breaker on makes it shut down is there short or abad breaker

What happens when you try? breaker trip? shut downs unit? what code flashes on the units start switch? Does the HVAC run ok on shore power? Does it happen when the HVAC runs turns off, then back on in less than 5 mins (high head pressure and locked rotor start current) Please give more details

Could be as simple as turning off "Summer Mode" that should only be used in very hot climates.
Hold both temp buttons (+ -) in until icon on display is gone.

What is the Spec number?
Also can you read a fault code on the start switch?
Do you know how to read the codes and post? if not let me know

You gave a lot of information, but you didn't say if it worked when free wheeling. If not, I would suspect the inertia switch. If it is working, you should hear it click when the motor is winding down after being shut off, at least when free wheeling. A 20 amp breaker will certainly handle a 15 FLA motor, even on startup. They don't trip at 20 amps exactly, especially on a simple overload. Even at twice the rated amperage, it can take several minutes to trip it. They will trip quickly on a dead short, however, or a severe overload. I doubt the windings are shorted or it either wouldn't work (start windings) or would run at a slower speed with the inertia switch constantly tripping in and out with it coasting while tripped in (i.e., accelerate, coast, accelerate, coast, etc.)

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.

on your generator ther is a reset if thats not it check for fuses if still no then u neda check the wires in the pluges if no then ur generator it self needs re bilt

it sounds like a short on that breaker

If the govenor didn't work that means that you placed the linkage on the carberator the wrong way. This will cause the genset to overspeed and possibly stop the genset from creating voltage. If the genset does not create voltage then you won't have a charger. Fix the linkage first by looking to make sure that the throttle plate is closed before starting genset. Once you start the genset check for voltage.

In short - NO. 15 amp circuits are intended for lighting and outlets and usually have 14 gauge wiring. A 20 amp circuit is usually wired with heavier 12 gauge wire which can carry the increased amps. If you plug in a 20 amp breaker into a 15 amp circuit you run the risk of overheating the smaller gauge wire and starting a fire.

you have a week breaker or a breaker that is to small you need a 40 amp breaker 20 on each side (two breakers locked into one) or worse you have a short in the dryer. If dryer runs for a little bit and then shuts down its the breaker.if it throws breaker as soon as you plug it in or start it then the short is in your dryer good luck