My guess would be a short between the inverter and the plug.
1 ) The diagram I show has two solid red wires from the inverter to the plug. inspect those for shorts.
2) Between the a/c windings and the inverter are three wires (red with black stripe), (red), and (red with white strip). They all come together in the windings (called a y-connected induction ) Meaning that any two of the three wires measured with a Ohm meter should read the same resistance through the windings. If you find a pair that shows a decreptancy, than you may have a shorted winding. Or you could have a winding with a direct short to ground.
I don't have anything in front of me as far as troubleshooting manual, All Ihave is a copy of a wiring diagram. Take this info for what it is worth.
Don't get yourself electrocuted with the case off while it is running, all the heat in the inverter is comming from electricty somewhere. you are just not seeing it at the plug..
Good luck,
Friiy