Furnace Fan Limit Switch Settings

The fan limit switch on a heating furnace controls when the furnace blower fan turns on and off.

Furnace fan limit switch settings.

This control also provides a safety limit that turns off the burner or furnace if temperatures at the furnace are too high. Setting the fan limit control switch properly will prevent damage to the furnace. The flames would raise the. The fan limit switch also has two other functions.

The furnace combination fan and limit control fan off setting blue arrow in our photo at left lets the furnace blower continue to run for an interval after the furnace burner has turned off but will shut the blower off after the heat exchanger has been cooled down and the heat it contained has been sent to the occupied space. Setting the middle arm at this temperature ensures that the fan will switch on at the correct time when the furnace warms ups. For example if the blower motor stopped running then no air would move through the unit. Set the temperature on the middle component to approximately 105 to 115 degrees fahrenheit.

High limit switch a high limit control switch will turn off the gas to a furnace if the temperature becomes too high. It works off of temperature and also provides a high temperature safety limit this is a switch actually two switches which turns the furnace blower on and off based on the temperature of the heat exchanger. In many models it also has a built in safety control for the burner to shut off at higher temperatures if the burner s inner control malfunctions. The fan limit control switch on a furnace regulates when the blower will come on or shut off.

Fan limit switches are used on all types of building heating furnaces. Step 6 set the arm to left of the middle component to approximately 90 degrees fahrenheit. 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.