These rooftop A/C units are usually durable and long-lived. All refrigerant connections are totally soldered together. No connections and hoses like automotive. Not even service ports (that can leak) like residential central systems.
Try a 30-amp campground pedestal-type supply. At least a 20-amp with a short heavy duty extension cord. I hope not, but your genny may be inadequate. At least be sure you're using a heavy cord.
Remove the plastic shroud. Rest your hand on the top of the compressor (NOT a connection!) while somebody turns A/C on. Do you feel it run? Two metal tubes will be connected to the compressor. The smaller one should get warm (HOT after a long run) and the larger one should cool (and finally get COLD).
Disconnect power and take the small cover off the driver side sheet metal that hides the capacitors. Take pix of capacitors and the nearby wiring diagram. Post them.
