The freezer is working but the fridge is warm. I checked the evaporator coil and it's full of ice built up. I checked the defrost heater and the defrost thermostat and both are ok. I can't find the defrost timer so I think it uses an electronic defrost. I also found a thermistor mounted on the back plate of the evaporator. What could be the problem and what is the purpose of the thermistor and how is it connected in the circuit? I called Sears and they don't provide the schematic diagram. Any help you could provide is very much appreciated.

Ben