Having seen this problem before in other equipment so I had an idea where to look. Problem: the automatic defrost function was not operating. Looking through openings in the back panel of the freezer compartment, you could see the evaporator coils and fins were a solid chuck of ice. There are three logical components to check. Heater
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element, thermostat (located just above the evaporator) and a relay on the control board (located in the fridge control panel). Checked the heater with an ohm meter -- OK. The thermostat closes the circuit at around 20 degrees and opens at around 32 degrees. Pulled out the thermostat, wiring, fan unit. Everything unplugs, unscrews, and unclips, don't cut wires. Put the whole assembly in a friends freezer for an hour or so to see if the thermostat closes -- OK. Problem had to be with the control board. Replaced control board, reprogrammed it per included instruction. Everything is working again.
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