What describes how a bi-metal fan switch operates a blower motor in a gas furnace?

The bi-metal fan switch in a gas furnace is designed to control the operation of the blower motor based on temperature changes. When the furnace heats up, the bi-metal strip in the fan switch bends due to the increase in temperature. This bending action is what triggers the switch to turn the blower motor on, circulating heated air throughout the home. Once the temperature reaches a predetermined level—indicating that the heat exchanger has cooled to a safe temperature—the switch then activates again to turn off the blower motor.

This operation allows the fan to run only when there is enough heat to distribute effectively, which is why the correct description of its operation is "temperature on-temperature off." This method ensures efficient heating and prevents the furnace from blowing cool air once the heating cycle is completed.

In contrast, other options do not accurately describe the operational mechanics of the bi-metal fan switch: an on-off mechanism does not account for temperature variances, continuous operation would not allow the fan to turn off when the furnace cools, and a manual override only reference suggests that the system is not capable of automatic temperature-based control, which is a key feature of the bi-metal switch functionality.