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How to Identify Blower Motor Capacitor Issues

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blower motor capacitor issue

A furnace capacitor is a small but important component that regulates power input to the blower motor. An issue with it can cause a furnace to malfunction. Fortunately, replacing a capacitor is one of the more affordable furnace repairs, but the issue can be hard to identify without a trained eye. We’ll look at a few blower motor capacitor issues to help a technician focus their heating repair efforts.

Signs of a Faulty Blower Motor Capacitor

The following signs can help identify a capacitor that’s stopped working or is failing:

  • The Blower Motor Isn’t Receiving Power: If the blower motor isn’t powered, then it will not turn on. First, check the fuse in your furnace (if it has one) or the circuit breaker it is connected to (in the main electrical panel). Consult with the owner’s manual or manufacturer to determine where the unit’s fuse is. If the issue isn’t due to a blown fuse or tripped circuit breaker, your furnace likely needs a new blower motor capacitor.
  • The Blower Motor Is Slow or Inconsistent: A failing capacitor can cause the blower motor to run slowly or fluctuate in speed. The motor can also overheat, short cycle, or run erratically. Call a professional if any of these issues occur. They’ll check for a faulty capacitor and replace it to restore normal performance.
  • The Capacitor Makes a Humming Sound: A humming noise is typically a sign of an electrical issue. You can check if the capacitor is working properly by turning up the thermostat; when the blower starts running, open the access panel and listen for any sounds from the blower housing. If you hear a humming or the fan is louder than usual, the capacitor may be weakening and may soon fail.
  • The Capacitor Has a Visual Fault: A bulging top vent means the capacitor has failed; an electrolytic discharge breaks the top vent to prevent damage to nearby components. The bad capacitor may instead bulge at the bottom if the gas pressure doesn’t break the top vent. Also, look for broken terminals or a burnt, cracked, or damaged casing.

Frequently Asked Questions

How Do I Test the Blower Motor Capacitor?

The traditional way to check a capacitor is to discharge it using a resistor (while wearing safety goggles). The resistor has two leads; connect each lead to opposite sides of the capacitor and a 230 VAC supply for a few seconds. A spark should occur when you remove the leads. If there’s a weak spark or none at all, the capacitor should be replaced.

Please note this method is risky, so it’s best to have a properly equipped and protected technician check for a blower motor capacitor issue.

A multimeter can also be used to test the capacitor. You can discharge the capacitor with the multimeter by touching the probes to the terminals; the reading should stabilize. There are a few options for testing, each requiring several steps. You can set the multimeter to:

  • Capacitance mode
  • Resistance mode
  • Continuity mode

It’s also possible to test the capacitor with a voltmeter or measure the time it takes to charge the capacitor (which requires removing it). But instead of explaining these steps in detail, we  recommend you call QRC, and our technician will safely and quickly identify and replace a bad capacitor.

Why Do I Need a Furnace Capacitor?

Capacitors regulate the flow of electricity. Having sufficient power output to the blower motor ensures it can run even when your HVAC system isn’t in heating mode. Running the fan can improve air circulation and air quality.

The capacitor also maintains a steady power input. Otherwise, electricity can fluctuate and damage the motor. The system has run capacitors that manage power input while a component is running and start capacitors to regulate the higher power input needed to turn on equipment. Most furnaces have run capacitors that provide both functions.

What’s the Life Expectancy of a Furnace Capacitor?

Capacitors have an average lifespan of 10 to 15 years. If a capacitor has to work harder, it can fail sooner.

What Causes a Capacitor to Fail?

The capacitor can fail because it’s at the end of its lifespan. It can also be damaged if the motor is under strain due to a different furnace problem. Prolonged exposure to heat, incorrect voltage ratings, and improper sizing and installation can cause a capacitor to fail as well.

Can I Replace the Capacitor Myself?

It’s not the most difficult furnace repair, but for safety reasons, we strongly discourage you from attempting to replace a blower motor capacitor. The job requires working with high-voltage electricity. Therefore, you risk a serious or fatal injury or causing major damage to your furnace by installing the part incorrectly. You also risk voiding the furnace’s warranty. 

Call QRC If You Have Blower Motor Capacitor Issues

Homeowners in Winston-Salem can trust QRC for any type of heating repair. Our licensed, trained professionals provide prompt repairs to avoid a major breakdown and prolong the lifespan of heating equipment. Prompt service also improves your comfort and safety. We can often perform a minor fix such as replacing the blower motor capacitor, and inspect the unit for other issues to resolve. To request heating repair service 24/7, call (336) 827-9143.