Thermistors are a component in refrigerators, furnaces, air conditioners and other systems that need to manage temperatures. In refrigerators, the thermistor is a key part of the system that allows the refrigerator to stay within a short range of temperatures and turn on its cooling cycle when the temperature starts to rise. Problems with the thermistor will keep the refrigerator from operating correctly.
The thermistor is designed to measure temperature where it is located. It is a simple metal device that channels an electrical charge within the refrigerator compartment. Thermistors can take many different shapes, but are usually small capsule-like components that are protect by a plastic shield.
The thermistor works through its resistance. It is made from highly specific metal alloy combinations. When the electrical current passes through these metals, it encounters a certain amount of resistance. However, resistance is also affected by the temperature around the thermistor. By comparing the resistance of the thermistor at one temperature with its current resistance, the thermistor can sense how much the temperature has changed and whether it has gone up or down.
It is not enough for the thermistor to sense what the current temperature is, it also needs to communicate this information to the primary thermostat system of the refrigerator. So the thermistor reads its own resistance and sends the value to the control system. The control system is fitted with the necessary circuitry to interpret the value and alter the temperature.
Because the thermistor is dependent on its electrical current to work, it is also subject to electrical faults. A thermistor can burn out or malfunction and stop sending the correct signals to the thermostat. In this case, all thermostat functions might be working correctly, but the small thermistor might need to be replaced to solve the problem.