Furnace Heat Limit Switch

Once the plenum reaches a specific temperature the limit switch sends a signal to the air handler to begin running and delivering warm air to your home.

Furnace heat limit switch.

A limit switch is a device that s located under your furnace s supply plenum. It reads the temperature of the plenum and waits until it gets appropriately warm. Fan limit switches are used on all types of building heating furnaces. When the thermostat calls for heat the furnace burners ignite and begin heating the heat exchanger.

Watch the oil or gas burner. A furnace has two switches called a fan limit switch and a high limit switch these switches can be separate or in one package called a combination switch. High limit switch a high limit control switch will turn off the gas to a furnace if the temperature becomes too high. The fan limit switch on a heating furnace controls when the furnace blower fan turns on and off.

This control also provides a safety limit that turns off the burner or furnace if temperatures at the furnace are too high. This happens because the flames are not being drawn into and throu. Initially the air above the heat exchanger in the supply plenum is not warm enough to blow into the house so the limit switch keeps the blower off. The limit switch plays an important role in every normal cycle of the furnace.