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9.9 High Limit Thermostat - FFLE3911QW and FFLG4033QW
9.9.1 General Characteristics
Thermostat is a device that is used to control a heating or cooling system so that it maintains a
certain temperature or maintains the temperature within a certain range. It acts as a switch that
opens or closes the circuit. If the temperature rises beyond the specified range, it opens the circuit,
else the circuit remains closed.
Function of Hi-Limit Thermostats:
• Based on 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 very hot. This will force open the circuit providing power to the
heater once the temperature reaches at a certain point within the dryer. This allows the Hi-Limit Thermostat to act as a
secondary safety option for the rimary thermostat, and also for other components such as the Thermistor and Blower.
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 to switch ON and OFF to
prevent the temperature from rising too high within the dryer. The Hi-Limit thermostat will remain unaffected through
all these cycles, because the temperature inside the dryer will remain lower than what is required to activate the Hi-Limit
sensors (generally 250-°Fahrenheit, though the exact temperature may vary).
Conditions that activate Hi-Limit Thermostats:
• If the temperature within the dryer exceeds the temperature allowed by the Hi-Limit Thermostat, the unit will activate
and turn off the power to the dryer’s heater. There are several 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, includes 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.
Wiring Diagram - FFLE3911QW
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