Either the relay is broken or the thermostat. I know this because I could force the fridge to run by hotwiring 220V across the common and run pins then briefly jumping the start pin to the run pin (thus sending 220V through the start winding for a split second).

The thermostat assembly has too many wires to know what to measure resistance on. But I figure that the thermostat can be black-box tested simply by checking whether it sends 220v to the relay switch. There are THREE wires involved (in addition to ground). With the relay removed (thus compressor disconnected), I plugged the fridge into mains. Got these measurements:

common pin to run: 220v
common pin to start pin: 20v

I’m tempted to conclude that the start winding /can/ accept 220v (proven by hotwiring), but 20v is also sufficient to cause enough motor movement to get it started. Does that sound reasonable? Can I conclude that the thermostat works and the relay is toast?

It’s hard to be confident without a service manual, particularly when the relay¹ has continuity. The common pin goes through a cylinder marked “Klixon MRP342LZ-32Q1”, which as 0.5 Ω. The start and run pins go through what seems to be a ceramic disc having 45 Ω. Is that reasonable?

I am ½ tempted to attach the relay, bypass the thermostat, and wire the relay to mains with start-run jumped persistently. Is that crazy? I assume the relay would internally disconnect the start winding. The fridge has no fans AFAICT, so no need for anything else to have power in this test.

¹ The relay I have has part № “A 3B7 8100” printed on it, which I cannot find online. But it looks exactly like this one.

Update

I hot-wired the relay. It was non-trivial because the relay has /3/ inputs. After studying it closely, I realised that one of the inputs (apparently for the start winding) is phony. The spade connector that attaches to it ultimately goes nowhere. When connecting the remaining 2 pins to load and neutral for the house mains, the fridge started and ran just fine.

Thus I have to conclude that the thermostat went bad. And replacements are not sold. However, Amazon has what’s claimed to be a universal fridge thermostat. It’s cheap, but I boycott Amazon. I think I will wait until someone throws out their fridge. Perhaps I can just take any thermostat and make it work.