The pencil fix didn't work for long, it went back to warming up. So I emptied the freezer section and took off the evaporator cover. And of course it was completely iced up. Here's what I found:

The defrost thermostat looked like the potting compound had pushed up out of the metal but it tested closed so I don't think it was necessarily bad, but it didn't look right.

The heater tested OK (I think) about 22 Ohms, certainly not open like I would expect if it were bad, but 5 amps is higher than I would have expected, but then I don't do this for a living so it doesn't much matter.

I couldn't find a "Defrost Timer" to test, so I assumed it was a function of the control board, or "Mother board" if you will. The control board didn't have any obviously burned spots on it, so I just tested the defrost relay by putting my Ohmmeter across the LINE and DEFR pins and energizing the relay with 12 volts. (After finding the protection diode and noting it's polarity.) It worked fine.

I completely deiced the evaporator, and put everything back together and turned it back on. Don't think my food will last much longer in the coolers. :-)


The only thing at this point that made sense to me is that the defrost thermostat is perhaps intermittent. I removed it and connected the two leads together until I receive the new one that I ordered. We'll see how it goes from there.