You may not even be consciously aware of it, but during the coldest days of winter, there’s comfort in hearing that “clicking” sound. You know the one; it’s the sound that indicates the thermostat has detected a decrease in the home’s temperature and has alerted the furnace’s control board to begin the ignition process so warm air will soon be circulating through the venting.
But what if that warm air never seems to arrive? Now you’re on your knees with your palms held inches from the floor vent, hoping to feel at least a little heated air eking out. If you’re experiencing little-to-no heated air circulating through the home’s venting, it’s likely that some aspect of the furnace’s blower system has failed.
How the furnace blower is supposed to work
A furnace’s circulation blower fan motor will run at multiple speeds to improve efficiency. 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.
Once the 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), 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 heat exchanger, and force the now-heated air through the home’s venting.
Keep in mind, the most important factor in efficient furnace operation is air circulation. 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 ensure good air flow. And, while it should go without saying, we’ll say it anyway: the furnace filter should be checked regularly and replaced at least twice a year. A clogged filter will greatly reduce the furnace’s efficiency and impede the air flow coming through the vents.
4 reasons why the blower may not be working
If you’ve been diligent about replacing the furnace filter and keeping the area where the furnace is located free of air flow obstructions, some kind of defect in the furnace’s blower system is likely responsible for the lack of heated air circulating through the home. Ready to start troubleshooting? Here are the top four things you should investigate:
- Incoming power problem – Let’s get this one out of the way first. The blower won’t run if there is a problem with the incoming power. Make sure the furnace’s on/off switch is in the “on” position and check to see if the circuit breaker controlling the voltage to the furnace has tripped or a circuit box fuse has blown. If there is no problem with the incoming power, we can move on.
- Malfunctioning blower motor – As mentioned earlier, the circulation blower fan motor draws air through the return vent, and then blows that air past the heat exchanger before forcing the air through the home’s venting. You should first confirm the blower motor is receiving power. You can do this by using a multimeter. Set the meter to “Volts AC” and carefully contact the meter’s red and black probes to the terminals of the incoming power wires connected to the motor. The meter’s display should indicate if voltage is present. If the motor is receiving power, but doesn’t run, the motor has probably burned out. Does the blower motor just hum? Does the blower wheel attached to the motor shaft have trouble rotating freely? Then it’s likely the motor bearings are locked up. Since the bearings can’t be replaced, you will need to install a new blower motor to fix the problem.
BONUS TROUBLESHOOTING TIP: If there is an obstruction in the blower wheel preventing it from turning, that could be the source of the problem. Confirm there is nothing obstructing the blower wheel and that the set screw securing the wheel to the motor shaft is tight. If the blower wheel is damaged, you should replace it with a new one.
- Faulty capacitor – The capacitor stores an electrical charge and then releases it in order to start the blower motor. If the blower motor does not start, or starts slowly, the capacitor may be faulty. When a capacitor fails, it will often bulge or leak. Even if you don’t see any visible signs of failure, you can test the capacitor using an analog-style Ohm meter or a capacitor tester to determine if the component is capable of storing and releasing its charge and whether it is operating with an acceptable capacitance rating. Be aware: before you handle the capacitor, you should release the potentially stored electrical charge to avoid injury. You can do this by placing a screwdriver with an insulated handle across each set of terminals (be careful not to touch the screwdriver blade when doing this).
- Defective control board – Since the control board regulates the power supply to all of the furnace components, a defective board could be responsible for the blower not running by failing to send voltage to the blower motor. Control boards are not easy to test for component failure, so you should confirm the blower fan motor, blower wheel, and capacitor are all functioning properly before considering replacing the control board.
Once you’ve determined the reason for your furnace’s blower not running, Repair Clinic.com will make it easy to find the right blower motor, blower wheel, capacitor, or control board to solve your problem. Enter the full model number of your furnace in the Repair Clinic website search bar, then by using the “Part Category” filter (Examples: “Motor”, “Blower Wheel & Fan Blade”) and “Part Title” filter (Examples: “Blower Motor”, “Blower Wheel”), you’ll be able to identify the specific part that will work with your particular furnace. In addition to carrying original manufacturer replacement parts from such top names in heating and cooling as Bryant, Lennox, Goodman, Rheem, York, Coleman, Ruud, Heil, or Payne, Repair Clinic also supports do-it-yourselfers and technicians alike with scores of heating and cooling product procedural videos, articles, and diagrams.