Once the weather turns chillier you’re going to rely on your furnace to keep your home comfortably warm on a daily basis. If you haven’t already done so, there are some important steps you should take to prepare the furnace to work at top efficiency this coming winter. One of those steps is to turn the furnace on right now to make sure everything is working properly and that includes the unit’s circulation blower fan motor. The blower fan motor is responsible for drawing air into the furnace to heat it and then force the heated air through the home’s venting to keep the room temperature at a comfortable level. A defective blower fan motor will result in no air flow whatsoever making the furnace incapable of keeping your home warm.
If the blower motor isn’t working, you’re going to want to determine if the motor is receiving voltage. This article will guide you through this voltage testing procedure, but let’s look at how a furnace circulation blower fan motor operates first…
Furnace circulation blower fan motor operation
As noted above, a furnace’s circulation blower fan motor is the component responsible for all air flow into and out of the furnace.
The blower fan motor runs at multiple speeds to improve efficiency
The blower fan motor is versatile and will run at multiple speeds to improve efficiency depending on if the component is being used to move heated air during the colder months or cool air during the warmer ones. Lower speeds (example: 750 CFM, or cubic feet per minute) are used when the furnace is heating, and higher speeds (example: 1220 CFM) are used to circulate cool air drawn in by an outside condensing unit when the furnace is part of a central air conditioning system.
The control board sends 120 volts to the blower fan motor
Once a gas furnace’s combustion sequence has completed (the inducer fan motor draws air into the burner assembly and the gas valve opens to allow gas to flow over the igniter which ignites the gas into a flame) or an electric furnace is prepared to heat the air with its heating element, the control board will send 120 volts to the circulation blower fan motor. The blower fan will then draw air through the return vent, blow it past the gas furnace’s heat exchanger or the electric furnace’s heating element, and force the now-heated air through the home’s venting.
Make sure the blower fan motor can do its job efficiently
Since we’re talking about air circulation, it’s important to ensure the circulation blower fan motor is allowed to do its job efficiently. To ensure the air is being circulated properly through the home, the furnace itself should be located in a well-ventilated area. Avoid placing boxes or other storage items in close proximity to the furnace. If the furnace is located in a closet, the closet door or doors should be louvered, or space left at the bottom of the door, to enable good air flow. And, finally, check the furnace filter regularly and replace the filter with a new one at least twice a year. A clogged filter will greatly reduce the furnace’s efficiency and impede the air flow coming through the vents.
How to test for voltage reaching a furnace circulation blower motor
A circulation blower motor that never turns on could be caused by a fault in the motor itself or due to the failure of another furnace component. To help determine this, you should use a multimeter to test for voltage reaching the motor. Here’s how you can do it:
Since you will need to remove one or more panels to access components inside the unit, be sure to shut off power to the furnace before beginning any disassembly. This will help you avoid getting an electrical shock if you accidentally touch an exposed wire or electrical component.
Your next step is to access the furnace’s control board. While the blower fan motor itself is normally supported on rails near the bottom of the furnace, the motor power wires are connected to the control board that is often located in an upper compartment. This may require you to remove both a lower and an upper access panel from the front of the unit.
With the panel or panels removed, you should discharge the run capacitor to avoid another potential shock (capacitors can still hold a charge even after the power has been turned off to the furnace). To discharge the component, place a screwdriver, or a pair of needle-nose plies, with an insulated handle across each of the capacitor’s terminals – avoid touching any metal portion of the tool when doing this.
Refer to the furnace’s wiring diagram to identify the circulation blower fan motor’s power input wires, then disconnect those wires from the control board.
Look for a voltage designation on the motor itself or in the wiring diagram, then set the multimeter’s range selection dial to the appropriate “Volts AC” or “Volts DC” setting.
Restore power to the furnace (with the power restored, you will need to be careful to avoid touching any electrical components with your bare hands).
Be aware, you may need to press in an access panel switch button to maintain the power supply. You can often use a clamp to hold the button in while you conduct the test.
Set the home’s thermostat to call for heating.
Wait approximately 90 seconds then contact the meter leads to the power input wire terminals for the circulation blower fan motor.
Observe the meter display. If the display indicates that voltage is present (example: close to 120 volts should display if the motor runs on alternating current), and you’ve already confirmed the run capacitor is working properly, then it’s likely the motor is defective and will need to be replaced. However, if the meter display indicates that no voltage is reaching the motor, then the furnace control board is probably at fault and a new board will need to be installed.
More furnace repair help from Repair Clinic
Want to learn how to install a new circulation blower fan motor in a York model TG8S080B12MP11A furnace or how to fix your model ML180UH110P48C53 Lennox gas furnace by replacing the flame sensor? This information and much, much more is available to you free of charge as part of Repair Clinic’s “Videos & Articles” content library. From troubleshooting and repairing HVAC units to major home appliances and outdoor power equipment, Repair Clinic has thousands of procedural videos, step-by-step guides, and schematics to assist you. Just enter the appliance/product/equipment model number in the search bar to get started.
You can trust Repair Clinic to stock only genuine original equipment manufacturer (OEM) replacement parts so you can be assured you’re purchasing a part specifically designed to work with your furnace, whether it carries the Bryant, Lennox, Goodman, Rheem, York, Coleman, Ruud, Heil, or Payne branding. To find the exact circulation blower fan motor, capacitor, control board, or any other part, that matches your unit, simply enter the full model number of the furnace in the Repair Clinic website search bar. You can then use the “Part Category” and “Part Title” navigation filters to refine that initial comprehensive part list to locate the precise component that will fix your furnace.