How to Troubleshoot an HVAC Combustion Motor

Blower Runs Continously

• 1

  Remove the furnace door and listen to the combustion motor blower. The furnace door usually has rows of fins and pops off with a flathead screwdriver. The combustion blower sits underneath the furnace flue vent and has a round-like shape with spokes at its center. A small tube runs out of the bottom or side of the blower component. This tube connects with the pressure switch component, which tells the blower motor when to turn off. Rather than turning off for each heating cycle, the blower motor fan runs continuously.

• 2

  Check the room thermostat to see if it's set for continuous fan operation. Normally, the combustion blower motor should only run for 30 to 60 seconds at a time. A thermostat set at the continuous setting will cause the motor to run continuously. Listen to see if the blower shuts off at normal intervals.

• 3

  Reset the furnace fan limit control switch. The fan limit control switch sits just underneath the furnace draft hood inside a small rectangular box compartment. Push the white button that protrudes from the box. This is a manual switch that resets the combustion blower device. Listen to see if the blower shuts off at normal intervals.

Blower Runs Frequently

• 4

  Turn off power to the furnace using the switch on the furnace service panel.

• 5

  Push down on the belt assembly that runs off the combustion blower device. If the belt depresses more than 1 inch at its center, the belt assembly may require tightening or replacement if areas on the belt are frayed.

• 6

  Check the heat anticipator setting inside the room thermostat box. The heat anticipator regulates when the blower motor turns on and off as room temperatures approach the thermostat setting. The heat anticipator’s setting should correspond with the manufacturer’s recommended setting as listed in the furnace service manual.

Blower Doesn't Run

• 7

  Turn up the room thermostat to trigger the start of a heating cycle.

• 8

  Check to see if the wheel on the combustion blower motor spins. If the wheel doesn’t spin, it may be stuck or seized up.

• 9

  Attach a volt meter or gauge to the electrical line that runs to the combustion blower motor. Blower motors typically have a 115-volt requirement. If the gauge reads less than 115 volts, the motor is not receiving the electrical current needed to operate.