Honeywell furnaces have a combination control, also known as a fan limit switch, that you can adjust to control the settings on a central heating system. To protect the temperature sensing element, steady the faceplate dial while moving the sliding pointers on its face. Never turn the silver control dial by hand; this could cause damage to the system.
The off setting of the furnace combination fan and limit control is located at the bottom of the control dial. This setting allows the fan to keep blowing after the furnace burners have turned off. The fans stop after the heat exchanger is cool. The "Fan Off" setting is a metal rod located to the far left of the dial. Adjust this control so that the fan does not send cool air into a heated space.
The "Fan On" switch is located just to the left of the "Fan Off" setting and controls the furnace blower. When properly adjusted, this switch ensures the fan does not blow cool air into a space you want to heat. Adjust the "Fan On" control to a minimum of 20 degrees above the "Fan Off" set point. Set it to a maximum of 30 degrees below the "Limit Off" set point.
The "Limit Off" indicator is located on the top right portion of the control dial. This safety control shuts down the furnace if temperatures exceed the maximum temperature setting on the combination control. Set the temperature according to the specifications for your model of Honeywell furnace. For the L4064B model furnace, set the "Limit Off" indicator to between 100 and 250 degrees.