How does a bi-metal fan switch operate the blower motor on a gas furnace?

The bi-metal fan switch operates based on the temperature of the furnace. It is a device that contains two different metals that expand and contract at different rates with temperature changes. When the gas furnace heats up, the temperature rise causes the bi-metal strip inside the switch to bend and make contact, which activates the blower motor. This action allows the blower to circulate warm air throughout the living space effectively.

Once the temperature drops below a certain threshold, the bi-metal strip relaxes, breaking the contact and turning the blower off. This cycle ensures that the blower motor operates only when needed, providing efficient temperature control and preventing unnecessary energy use. This temperature-dependent operation distinguishes this method of control from other systems that may rely on time-based or voltage-controlled mechanisms.