The limit switch energizes the fan circuit when warm air in the plenum of the furnace reaches a preset temperature. When the desired temperature in the home is reached, the furnace burner shuts off, but the blower fan continues to operate until the temperature of the plenum falls to the lower limit switch setting. How to Replace a Furnace Fan Limit Switch | eHow Was this helpful? How to Install & Wire the Fan & Limit Controls on Furnaces Wire the Fan & Limit Controls on Furnaces Honeywell & White Rodgers Fan Limit Controllers , How to Install and Wire the Honeywell L4046B combination Furnace Fan Limit Switch Control: Advice for Installing and Wiring the Furnace Combination Control Fan Limit Switch on Heating Systems Guide to Installing & Wiring Fan Limit Switches on Warm Air Furnace Heating Systems Furnace Combination How to Reset a Furnace Limit Switch - Hunker The function of your furnace limit switch is to tell the fan when to turn off and on depending on the temperature in the home. It's possible to reset the switch at home when necessary by following a few simple steps. However, for your own safety, don't attempt to reset the switch without first consulting your furnace's instruction manual.