I would agree with Son of Norway. There are multiple places where the A/C voltage, both the positive and the negative, gets from the camp ground post to the air conditioner. If you have a wire that is just a bit loose, that totally upsets the voltage at the end.
I would definitely try rigging up a heavy duty extension cord from the post up to a roof top connection at the air conditioner to prove whether it's a power problem, or something else.
A No. 12 wire extension cord can be connected to a new post plug at one end, and the other end connected up on the roof. That is a pain, but certainly getting to all the respective screw connectors in the plugs and panels is also.