Without throwing more parts at the problem I get an amp meter, and a volt meter(separate)units. Turn on the A/C unit and monitor the amps & volts are doing. I'm thinking maybe your having a voltage drop problem which is causing the breaker to trip. Remember, when voltage goes down, amps go up. And also check the voltage at the source. And remember when the compressor starts the amps can be at least 8 to 10 times the running amps for a split second. Which an average amp meter will be able to read. Just me 2 cents worth.
