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here your furnace fan limit controler, the combination high-limit/fan control contains a normally open fan switch on the right side
On a call for heat, the burners are ignited. as the temperature of the heat exchanger, begins to rise, the bimetal begins to rotate turning the front dial with it.
even more The bimetal strip will first close the fan switch and start the fan motor.
and also if an overheating condition occurs due to insufficient airflow for example:
faulty fan motor or fan switch or dirty air filter and sometimes low fan speed.
and also The bimetal strip will continue to warp until the high-limit cut out temperature is reached and then opens the limit switch.
Similarly, when the limit switch is open, the control circuit finally de-energized, which causes the gas valve close.
Meanwhile, the fan continues to run until the fan switch cools to the fan -offset point.