Dometic AC Compressor won't stay running

As you figured out, you need the clamp on Amp meter to watch the compressor amps and what those amps are in that 20 to 30 seconds. Once the compressor starts there is no reason to suspect the start capacitor because it did its job. There is a limit on the compressor and the odds are your compressor is bad. The amp draw will show you that. IF the amps do not go over 15 amps and the compressor still kicks off, then the Freeze control is probably defective. IF you have a system doing what you have, then the compressor should attempt to start every few minutes. If not, that points to something telling the compressor to not start---The freeze sensor. Since you full time, a freeze sensor is cheap and easy to replace. I would do that regardless of your amp meter. Take that out of the loop by replacing it. You can also trace the freeze sensor to where you can separate the 2 wires and cut the wires and splice them together on the circuit board side. That will bypass the freeze sensor. Doug

Since you have 2 units, just swap the freeze sensors.