To check if your furnace fan is working, first turn your thermostat's fan setting from Auto to On. Listen closely at a nearby vent. If you feel no airflow and hear no humming, the fan is likely malfunctioning and requires further troubleshooting.
A bad furnace blower motor usually causes weak airflow, strange noises (screaking or grinding), overheating, or completely failing to turn on. The quickest way to check if it's dead is to inspect if the fan wheel spins freely by hand or if it has seized.
Learning how to reset your furnace blower motor is relatively simple, but there are a few steps to follow:
Start by turning the furnace off, turn your thermostat to “fan only,” and wait a few minutes. If you see or hear the fan turn on, your blower motor is not the culprit. If the fan does not start, you have a wiring issue (circuit breaker trips) or motor problem (circuit breaker does not trip).
To put it very simply, the furnace fan limit switch is a control that tells your furnace's fan when to turn on and off. So, when the furnace isn't on, it tells the blower not to operate (and send cold air into your home) and when the furnace is on, it tells the blower to turn on and start circulating the warm air.
To get your furnace to kick on, first verify your thermostat is set to "Heat" and raised at least 5 degrees above room temperature. Next, check that the furnace power switch (usually resembling a standard light switch on or near the unit) is toggled "ON".
In newer applications, the blower motor resistor is actually a solid state module that sends a varied signal to the blower motor. The traditional blower motor resistor is connected to ground and wired in series with the blower motor assembly.
If your furnace fan won't turn on, first check your thermostat to ensure it’s set to "Heat" and the fan mode is on "Auto." Next, verify that the furnace is receiving power by checking the circuit breaker and ensuring the safety door panel is tightly closed.
The $5,000 rule is a guideline to help homeowners decide whether to repair or replace their HVAC system. You multiply the age of your unit by the cost of the needed repair. If that number exceeds $5,000, replacing your HVAC system is often more cost-effective.
The heat exchanger is often considered the most costly part of a furnace to repair or replace. It is a critical component that transfers heat from the combustion process to the air that circulates throughout your home. Over time, heat exchangers can crack due to the constant heating and cooling cycles they undergo.
Your furnace’s reset button is typically a small, bright red or yellow button located either inside the blower compartment, near the burner assembly, or directly on the motor housing.
A furnace blower motor is the heart of your heating system. It's the part that pushes warm air from your furnace through the ducts and into your rooms. Without a working blower motor, your furnace might create heat, but that heat would stay trapped inside the unit.
Diagnosing a faulty blower motor versus a bad resistor typically comes down to what fan speeds are working. If the fan only works on the highest setting, the resistor is usually the culprit. If the fan doesn't work on any speed, or if it makes strange noises, the motor itself is likely failing.
On average, a furnace blower motor lasts between 10 and 20 years. However, this lifespan can be significantly shortened by a lack of maintenance, specifically if air filters are not changed regularly, causing the motor to overheat and overwork.
To reset a furnace blower motor, turn off the power at the circuit breaker or service switch, wait 5-10 minutes for it to cool down, and press the red or yellow reset button located directly on the motor housing. If the button does not stay in, the motor may need more time to cool or a professional repair.
One of the key benefits of running your furnace fan all the time is enhanced air filtration. This allows air to pass through your furnace's filters more frequently, which can significantly improve indoor air quality.
5 Warning Signs It's Time for Furnace Replacement
A standard furnace lasts between 15 and 20 years on average, though electric furnaces can stretch up to 20 to 30 years. Regular maintenance, such as annual tune-ups and changing your filters every 1 to 3 months, is the most important factor in reaching or exceeding this lifespan.
The "two-foot rule" in HVAC is a duct design and installation guideline that requires a minimum of 24 inches of straight, uninterrupted space between branch take-offs (where air taps off the main trunk). It is also applied to spacing branches away from end caps, transitions, and the main plenum.
To test a furnace blower motor, start by turning off the power and checking that the fan spins freely by hand. Then, use a multimeter to check the capacitor's Microfarad (MFD) rating and test the motor windings for electrical continuity or correct resistance.
Replacing a furnace blower motor typically costs between $400 and $1,500, with most homeowners paying around $900 for parts and professional installation. Your total cost largely depends on the motor type and whether your system is under a manufacturer warranty.
All furnaces are equipped with a reset button. They are generally red or yellow and are located inside the blower compartment. The reset button is a safety feature that will shut down the furnace when a problem is detected, often a hot or overheating furnace, before it trips the circuit breaker.
Modern furnaces typically take 30 to 90 seconds from the time the thermostat calls for heat until the blower fan starts pushing warm air into your home. This delay is completely normal and protects your furnace from blowing cold air into your home.
The fuse for a vehicle's blower motor (which controls the cabin fan) is usually rated between 30 and 40 amps and is typically located in the under-hood or interior fuse box. The exact name, amperage, and location depend entirely on the vehicle's make and model.
A bad blower motor relay will typically cause your HVAC system to produce no airflow, blow warm air only, or leave the fan running constantly. It often fails due to overheated electrical contacts or melted wiring.