How Dryer Thermistors Work

Dryer thermistors that control the heater are always in the airflow. Thermistors are heat sensors that change resistance with temperature. Dryer thermistors are wired directly to the dryer control board. The board constantly monitors the resistance of the thermistor for subtle changes as the heater heats the airflow. When the control board senses a specific resistance value it opens up the low voltage circuit to the heater relay coil. When power is cut off to the relay coil the heat contacts open interrupting the current flow to the heater. The heater turns off and the cycle starts over.

Notice on the drawing that the thermistor item #15 is located in the front of the blower housing directly in the airflow.

Typical Dryer Thermistor