What Does a Thermistor Do in a Dryer?

Thermistors are made from compounds of certain types of metals, called transition metals, including manganese and copper, and can be made in a variety of shapes to best fit the needs of the situation. They allow heat-generating appliances to monitor and regulate internal air temperatures.

Thermistors in Dryer Circuits

Dryer thermistors are located in the airflow conduit that carries heated air into the dryer's cavity, which contains clothes and other materials that are being dried. They are wired to a central circuit board, called a control board, that synchronizes the dryer's operations and processes user input. The control board reads the resistance levels of the thermistor to determine the temperature of the air being propelled into the dryer. The circuit board uses data sent from the thermistor to determine when it should cut power to the heating element and allow the drying cycle to restart.

Temperature Monitor

Thermistors are temperature-sensitive conductors. Their ability to conduct voltage is affected by the temperature around them. Some thermistors become less conductive as they are exposed to higher temperatures, but most become increasingly conductive as the local temperature rises. A dryer's circuit board is programmed to respond to the level of voltage conducted by the thermistor, which is determined by its current levels of resistance.

Benefits

The primary benefit of thermistors compared to other types of temperature-sensitive resistors, like thermocouples, is their sensitivity. Thermistors react to even slight changes in temperature. Some thermistors can accurately detect fluctuations of less than a single degree in temperature. The consistent sensitivity of thermistors helps prevent dryers from overheating, which could destroy the entire appliance.

Disadvantages

The sensitivity of thermistors also carries some drawbacks. Thermistors can be damaged or destroyed if temperatures fluctuate outside of the acceptable range. A broken thermistor may prevent a dryer from operating at all. Thermistors are also designed to handle radically different heat capacities, which means that dryers and other appliances require a specific type of thermistor to function. Thermistors are rarely interchangeable, so it can be difficult to find replacements for old, out-of-date appliances.