Function of Hi-Limit Thermostats
Due to the vast amount of heat produced by clothes dryers during the course of normal operation, it is important that a secondary safety option is available in case problems arise. A hi-limit thermostat serves as a safety feature that keeps the dryer from getting too hot, since it will force open the circuit providing power to the heater once the temperature reaches a certain point within the dryer. This allows the hi-limit thermostat to act as a secondary safety option for not only the primary thermostat but also for other components such as the thermistor and blower as well.
Hi-Limit Thermostats During Normal Operation
The standard position of the hi-limit thermostat is closed, allowing current to flow to the heater without interruption. Under normal conditions, the dryer's primary operating thermostat will cycle the heater on and off to prevent temperatures from rising too high within the dryer. The hi-limit thermostat will remain unaffected through all of these cycles, since the temperature inside of the dryer will stay lower than what is required to activate the hi-limit sensors (generally 250-degrees Fahrenheit, though the exact temperature may vary on some dryer models).
Conditions That Activate Hi-Limit Thermostats
Should the temperature within the dryer exceed the temperature allowed by the hi-limit thermostat, the unit will activate and shut off the power to the dryer's heater. There are several different conditions that could lead to this increased temperature, including faulty parts such as the primary operating thermostat, thermistor and blower. Other conditions that can lead to an increase in temperature significant enough to trip the hi-limit thermostat include the improper configuration of components, such as the primary thermostat or heater. Blocked or clogged vents can also cause a significant increase in the temperature within the dryer and are one of the most common causes for the activation of a hi-limit thermostat.