How to Set the Limit Switch on a Miller Mobile Home Furnace

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Miller Heating and Cooling, a division of Nordyne, produces residential HVAC equipment for manufactured housing, including mobile homes. Miller mobile home furnaces use internal limit switches to regulate when the blower fan turns on and off. If the fan in your Miller furnace runs too frequently or not frequently enough, you may need to adjust the fan limit switch settings. The process may be accomplished in minutes, even without previous furnace repair experience.

Things You'll Need

  • Screwdriver (optional)
  • Shut off the electrical supply to your Miller furnace. Look for a dedicated "On/Off" switch on the side of the furnace, or on the wall near the appliance; flip the switch to the "Off" position. Find the circuit breaker switch that supplies the electricity to the furnace and push it into the "Off" position, if your furnace model doesn't have a dedicated "On/Off" switch.

  • Open or remove the control access door on the front of the furnace. Pull the handle to open a control access door with hinges, or take out the screws securing a removable door to the furnace cabinet. Lift the door straight up and pull it toward you, if you don't see any hinges or screws. Remove the burner access door, if your Miller furnace has two front control panels.

  • Find the limit control box mounted to the top of the burner compartment. Look for a small rectangular box with a button protruding from it. Lift the cover off of the limit control box to access the fan limit control switches.

  • Hold the scale plate dial to prevent it from moving, while setting the "Fan On" and "Fan Off" limit switches.

  • Set the "Fan Off" limit switch to tell the furnace blower when to stop circulating cool air. Move the "Fan Off" limit switch to correspond to the 90-degree Fahrenheit mark on the scale plate dial.

  • Set the "Fan On" limit switch to tell the furnace blower when to energize. Move the "Fan On" limit switch to the 110-degree Fahrenheit mark. Adjust the "Fan On" limit switch if desired; the switch must be between 15 degrees above the "Fan Off" setting and 30 degrees below the "Limit Off" setting.

Tips & Warnings

  • Reverse the process to replace the removed furnace components.
  • When setting the "Fan On" and "Fan Off" limit switches, the temperature settings correspond to the temperature inside the furnace blower compartment, not the temperature of the home.
  • The "Limit Off" switch in Miller furnaces is a safety device that is factory-set to 160 degrees Fahrenheit; it cannot be adjusted. The "Limit Off" switch is located to the right of the "Fan On" and "Fan Off" limit switches on the scale plate dial.

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