Common on AC units to get ground leakage, normally this is from condensate water in the indoor unit from a blocked drain, which needs to be cleaned out along with the tray and the coils, as they do collect a lot of dust and salts. Outdoor unit as well will have some leakage, normally with inverter from dust on the bare PCB in the unit, as they are not normally enclosed and tend to collect dust as well. Brush off the PCB with power disconnected ( not turned off, the outdoor unit board is powered all the time with AC power connected to keep the communications link alive) after waiting 15 minutes after disconnecting, as the power supply there typically has 2200uF 400V of capacitance on it, or more, and that will bite. Leakage also common at the compressor terminals, remove the cap and clean it with some spray oil, wipe off and put the cap back on.