AC compressor won't run, tried new cap, 83 VAC at terminals

If the cap is the same as line voltage, you have a bad connection. Use the voltmeter to verify you have 115 volts to the trailer, plug into any receptacle. Turn on the AC, does the voltage drop? If yes, check the incoming line connections in the panel, clean and tighten. If no, check the line at the compressor, low voltage, check the connections at both sides of the breaker, throw it off-on a few times, recheck. Best guess, one of the above will fix it.

WDP