Gosh darned *%$! @! Cabin Refrig...?

That would be totally frustrating - I feel your pain...

Spent a week finding a faulty thermostat on a client's boat a few months ago (Older mechanical switch - I get my Refrigeration mate for the fully electronic stuff, I wouldn't know where to look with that stuff). Same sort of freaky no-particular-obvious-cause-or-pattern fault, and totally random.

It might have been several things - but the fault has not (yet!!) surfaced again. May well have been all the terminals and any solder joints getting cleaned, re-soldered, plugged together and blasted with sealer - but at least we know the thermostat is new and the owner thinks I'm a Guru 'cos his beer is cold.

Good luck!

Edit - Yep, relays are always a failure point, good call.

Nothing more annoying that an erratic failure.

I'd put my money on loose or corroded connections that are intermittently making/breaking. It's the marine environment that makes me think this...

If I was troubleshooting this unit, I'd pull it out and check line voltage at the compressor control relay to be sure power is reliably getting that far. And I'd be spending some time with a flashlight, a screwdriver, and a little wire brush making sure all the connections are tight and free of corrosion.

Possibly an AC to Dc power converter bad.Check to see if you have trickle voltage or full power at the 12 volt output side and then check the converter switch to see if you have a full 120 volts input.After a component in a circuit has been exposed to heat by charging and conversion to low voltage after a year or two it begins to lose its ability to hold the voltage and wattage values because of switching in the high to low voltage transformer it begins to work intermittently.so naturally if there is a drop in voltage or amperage it will not blow the fuse.But it will cause overheating of the transistor or capacitor,or integrated circuit.A zener diode controls the rise in current so it can cut the component off.

My money is on that 12 vt controller. That controller needs a good 12 vts to run either the 12 vt side or the 110vt side. So mine has a battery and solar charger all of it's own. Check you wiring, You may have it running thru the Perko master "off" switch. They also ran several relays in there to switch from 12vt fridge operation to 110vt operation and any one of them sticks, and she shuts down.