What is a Furnace Capacitor (Health Ohio)

Furnace capacitor in Newark Ohio

Expertise from a Professional HVAC Contractor in Health Ohio

One of the most important parts of a gas forced air furnace is the blower motor. This motor is responsible for moving fresh air through the furnace, over burners to heat it (or over the evaporator coil to cool it), then distribute it out to the home via a series of ducts. The blower motor is connected to a fan and fan cage (also called a “squirrel cage”) either directly or via a belt, and requires a “jolt” of extra power to get it turning to start blowing.

The job of the start capacitor is to store that extra power. When the thermostat and control board sends a request to start the motor turning, the capacitor sends that burst of power to get it spinning. A capacitor is a sealed unit, typically shaped like a small can, and can only be replaced, not repaired.

Signs of a Bad Furnace Capacitor

There are some telltale signs that the capacitor is at fault when your furnace or AC won’t start. Look for these signs and symptoms.

Symptom: Clicking Noise

Fortunately, a capacitor can show symptoms of failure before, or during a failure event. The first symptom is a clicking noise as the furnace is trying to start up, as the relays and switches attempt to send power to the blower motor. If you hear this noise, but the blower doesn’t start, switch the thermostat to off and call a professional HVAC contractor in Heath, Ohio to check the furnace.

Symptom: Acrid Burning Smell Coming from the Furnace

Often, the furnace will give off a burning smell in the vents, indicating electrical issues in the furnace. If you get any sense of something burning in the area of the furnace, switch the furnace off at the thermostat. You may also want to switch off the breaker at the home’s electrical breaker box to ensure further damage doesn’t occur to the heating system.

Note: A musty, dusty smell could be from an accumulation of dust on the burner and in the ductwork, but that type of smell usually dissipates within a short time of the furnace running again after a long summer off.

Symptom: Humming Sound from the Blower

When the start capacitor can’t send that burst of power, or can’t send enough power to the blower motor to start turning, often you’ll hear a “humming” sound coming from the blower motor. Sometimes, the motor will try to turn but seems like it’s binding or stuck. You can check this by setting the temperature on your thermostat a bit higher, then stand by the furnace to listen as it tries to start. You may hear a click as a relay sends power to the capacitor or motor, then the humming sound. A bad capacitor can also cause the circuit breaker or other safety devices within the system to trip, to prevent damage to the blower motor or other sensitive electronic parts.

Symptom: No Power At All

When the capacitor goes bad in a furnace, it may also cause circuit breakers to trip, or may not provide power at all to the blower motor to begin its operation because of an electrical fault in the capacitor. Either way, the blower motor isn’t getting power. Double-check the circuit breaker in your home’s electrical panel, and be sure the heating system switch is turned on (there may be a light-switch style switch near your furnace that controls power at the furnace). Turn up the thermostat, and wait for it to start. If nothing happens, it’s time to call for a professional HVAC contractor to check out your heating system.

Symptom: Erratic Motor Operation

The capacitor acts like a battery, holding a charge to get the blower motor spinning. All electricity going to the motor passes through the capacitor, even after it’s running. A bad capacitor might cause your blower motor to run slower than normal, run hot, and short cycle. If you notice your furnace stopping and starting erratically, it could very well be the capacitor.

Older furnace models may use separate start and run capacitors. The start capacitor is responsible for the extra burst of electricity to get the motor running, when the run capacitor takes over to regulate the power running to the motor. Newer furnace models have split capacitor motors that handle both functions, making it easier for our service technicians to diagnose and repair.

Don’t let a bad capacitor in your furnace ruin your day! If it appears you’re having one of the above issues with your furnace, call Dor-Mar Heating & Air Conditioning. We are available 24 hours a day, 7 days a week, every day of the year. We can arrive at your doorstep same day, if necessary.

Dor-Mar to the Rescue!

Schedule an appointment for HVAC system installation, troubleshooting or maintenance with us today by using our online contact form, or call one our Heath number listed below . We pride ourselves on our customer-focused service, and our reviews show it!

HEATH  740.640.6116

Dor-Mar…Your Climate Hero!

*Please note: neither the Centers for Disease Control(CDC), the World Health Organization (WHO), nor the manufacturer of our UV-C Devices have officially announced whether UV-C kills the current strain of Corona Virus (COVID-19). We urge you to err on the side of caution until we have a definitive answer, and take other measures to prevent the acquisition or spread of this virus.


In continuous operation since 1962, our expertise goes beyond just the mechanicals of your HVAC system. We’re pretty handy when it comes to ductwork and system-wide maintenance as well. For top-notch service keeping your home’s heating and cooling system clean and your family breathing clean, filtered air, contact Dor-Mar today.

Our team offers a wide array of routine maintenance and emergency services for your heating and cooling system, allowing your family to breathe fresh, safe, clean air and be comfortable year-round. We also offer a number of add-ons to your HVAC equipment that can improve your home’s Indoor Air Quality (IAQ), such as electrostatic air filters, whole-house humidifiers, duct cleaning, Ultraviolet-C lighting systems, and more.

Schedule an appointment for HVAC system troubleshooting or maintenance with us today by using our online contact form, or call one of local offices listed below. We pride ourselves on our customer-focused service, and our reviews show it.

Dor-Mar…Your Climate Hero!

Steven Brewer<br/>HVAC Expert & Owner

Steven Brewer
HVAC Expert & Owner

I started in the HVAC business as a young man, with my father putting me in crawl spaces to run ductwork while on summer vacation from school; I began full time in our family HVAC business at the age of 19. I obtained my state commercial HVAC license at 25. I'm married with three kids, and I love boating, fishing and hunting.

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