Re: A/C problem
It sounds to me as though your pedestal has one leg of the 50A power that is not working. It could be as simple as a bad circuit breaker. The 50A one is actually two breakers, one for each phase, that are fastened together and which are supposed to operate together, and do when all is proper. But there is a good chance that one leg is not closed. If you are still there, I would first try opening the breaker on the pedestal, pause for 30 seconds or so, then close it. That might reset the open side.
If you have a meter, check from each leg to neutral (120V each), from each leg to ground (120V each) from one leg to the other (should read 240V) and then between neutral and ground.(Ideally this should be 0V but could see a few volts here without problem.) I suspect that you will discover that one leg is at 0V.
If the voltage were just low you would probably hear a loud hum when it attempted to start and the water heater would work but just very slowly. A meter is the only way to be sure.