Lennox Gas Furnace: G23

Re: Inducer Motor Not Running

The furnace is receiving a call for heat, but the inducer motor is not running and ignition never takes place.

CHECKOUT:

1. Check Operation

• Place an amp probe on the Black wire going to the combustion motor.
• Start the furnace with a call for heat.
  • Inducer motor should start immediately.
    • Inducer Motor Draws Amperage but Does Not Run → Step 3. Check Inducer Motor
    • Inducer Motor Does Not Start & Draws No Amperage ⇒ Check the temperature of the inducer motor.
      • Motor Hot →  Step 3. Check Inducer Motor
      • Motor Cool →  Step 2. Check Control Board

2. Check Control Board

• Check for 24VAC between "R" and "C" at the furnace board.
  • No Power = Door Switch Open, Tripped Mini-Breaker or Open Limit Switch
• Check for 24VAC between "W" and "C" at the furnace board.
  • No Power = No Call for Heat ⇒ Recheck Thermostat
• Unplug the 2-wire connector feeding power to the inducer motor.
• Check for 120VAC in the plug coming from the control board.
  • 24VAC on "W" + No 120VAC at Plug = Bad Control Board

3. Check Inducer Motor

• Unplug the 2-wire connector feeding power to the inducer motor.
• Check for resistance through the motor windings.
  • No Resistance + Cool Motor = Bad Inducer Motor
  • No Resistance + Hot Motor = Internal Overload Open ⇒ Allow time to cool.
• Spin the motor manually by turning the cooling fan blades at the front of the motor.
  • Motor Spins Freely but Won't Start with 120V Power = Bad Inducer Motor
  • Motor Stiff or Difficult to Turn ⇒  Remove the vent and check for an Item Stuck in Vent Blower
    • No Obstruction ⇒ Oil the front and back bearings of the inducer motor then manually turn the motor until it is free enough to start on its own.
    • There are two, small oil ports on the top of the inducer motor.