Watch out: when adjusting the temperature settings in this control do not press on, bend, twist nor in any other way fool around with the rotating metal disc. Up the furnace heat exchanger and supply air plenum.ĭetails about setting the temperature controls on a fan limit switch are Such damage would make the furnace unsafe.īy keeping the fan off until the supply air plenum is warm, the heating furnace limit switch prevents the furnace blower from sending chilly air into the building if the oil or gas burner has not sufficiently heated This control also provides a safety limit that turns off the burner or furnace if temperatures at the furnace are too high.įan/Limit switches are used on all types of building heating furnaces.ĬLICK HERE to see a CLOSE-UP of the FAN OFF, ON, and HIGH LIMIT OFF factory settings on this fan limit control.Ī combined fan limit switch such as the Honeywell L4064 or the White Rodgers 5D51-90 limit control provides at least three heating blower fan temperature controls that respond to the temperature in the furnace supply air plenum:ġ- FAN OFF: the low temperature at which the furnace blower fan will STOP to prevent blowing cool air onto room occupants.Ģ- FAN ON: the temperature at which the blower fan will turn ON to begin to deliver heat to the building's occupied spaces.ģ- FAN LIMIT: the high temperature at which the high limit switch will open (turn OFF) to stop the burner to prevent overheating of and damage to the heat exchanger. The fan limit switch on a heating furnace controls when the furnace blower fan turns on and off. What is the Function of the Hot Air Furnace Fan Limit Switch? We also provide an ARTICLE INDEX for this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need. Sketch at page top courtesy of Carson Dunlop Associates. The sketch at the top of this page shows the typical location of a combination fan and limit control such as the Honeywell type L4064B, a control whose installation, settings, testing, & operation are explained in detail here. Causes of furnace blowing cold air at start-up of heating cycle. Guide to troubleshooting heating system furnace controls, limit controls, and fan controls.
Sensing Furnace Temperatures How to manually turn on a furnace or air conditioning blower fan. Which Way to Set the White AUTO / MANUAL Fan Control Switch. This article describes in detail the purpose, operation, setting, installation, wiring, and testing of furnace combination controls, also commonly called the "fan limit switch" on warm air heating systems.Ĭovered here: How to Wire the Fan & Limit Control wire and test the combination fan and limit control on a furnace. We have no relationship with advertisers, products, or services discussed at this website.įurnace blower fan limit safety switch installation & troubleshooting:
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