The box is now empty, disassembled and at room temp and I believe the issue is the ineffectiveness of the defrost cycle, which over time causes a buildup of frost on the damper for the FF section. Perhaps other blockages that I have not check for...
Performed some tests with ice on the Thermodisc with no definitive results. Instead of opening and closing, it registers a changing resistance value much like thermistor. Anyone know how to test this unit using ice cubes in a bowl of water? Attached is an online copy/photo if the part.
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Found another difference between actual wiring and available schematics. The schematic shows the over-temperature thermodisc to be in series with the Calrod defrost heater wiring, but I find that both are wired directly to the board.
The original Thermodisc shows it to be L65-20F and the current replacement part shows it to be L140-30F (opens at 140F and closes at 30F). Seems like that's a better arrangement than the opens at 65F which would allow the evaporator to get hotter. Appreciate any help with that.