Temperature Control Thermostat
The temperature control thermostat directs voltage to the compressor, evaporator fan motor, and condenser fan motor (if applicable). If the temperature control thermostat is not working properly, it may cause the refrigerant system to run longer than necessary. As a result, the refrigerator will be too cold. To determine if the thermostat is defective, rotate the thermostat from the lowest setting to the highest setting and listen for a click. If the thermostat clicks, it is not likely defective. If the thermostat does not click, use a multimeter to test the thermostat for continuity. If the temperature control thermostat does not have continuity at any setting, replace it.
The thermistor monitors the air temperature and sends the temperature reading to the control board. The control board then regulates power to the compressor and evaporator fan based on the thermistor readings. If the thermistor is defective, the compressor and evaporator fan may run too frequently. As a result, the refrigerator will be too cool. To determine if the thermistor is defective, test it with a multimeter. The thermistor resistance should change in conjunction with the refrigerator temperature. If the thermistor resistance does not change, or the thermistor does not have continuity, replace the thermistor.
Temperature Control Board
The temperature control board provides voltage to the compressor and fan motors. If the control board is faulty, it may send continuous voltage to the compressor or fan motors. As a result, the refrigerator will be too cool. Control boards are often misdiagnosed—before replacing the control board, first test all of the more commonly defective components. If none of the other components are defective, consider replacing the temperature control board.