How to Adjust the Limit Switch on a Lennox Fan

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Lennox is one of the most well respected companies in the field of heating and cooling products. Like other brands of furnace fans, the Lennox variety is regulated by a device called the limit switch. The switch serves as a control mechanism for the blower -- or fan -- and a safety control for the burner. Setting the gauge of the limit switch is simple and most consumers should be able to complete it with little to no supervision.

  • Take the cover to your Lennox furnace off. Unlatch or slide off the removable door and put it out of the way.

  • Look for the Lennox fan limit switch. It will resemble a small, shiny box that runs vertically near the ceiling of the furnace.

  • Open the cover to the device. Move it out of the way until you clearly see the inner gauge and the temperature settings.

  • Adjust the three settings to the proper temperatures suggested in your owner's manual. As a general rule, you'll want the lowest on the left at 90 to 100, the center at 130 to 140 and the final setting on the right for the burner at 200 to 210 degrees Fahrenheit.

  • Pull out the white switch to reset the furnace to automatic and finalize your adjustments. Within about 30 minutes, the fan will come on and shut off at the settings you've designated.

Tips & Warnings

  • Be sure to close the limit switch back up and return the cover to the furnace door.
  • According to Richard Jazwin in "Medium and High Efficiency Gas Furnaces," improper settings on the limit switch "could cause the fan or the entire furnace to overheat and malfunction."

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References

  • "Medium and High Efficiency Gas Furnaces"; Richard Jazwin; 2002
  • Photo Credit Jupiterimages/Comstock/Getty Images
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