Everything You Need to Know About AC Capacitors
Learn everything you need to know about your AC capacitor, from what it does, to signs that it may be going bad, to the importance of HVAC maintenance in prolonging the life of your capacitor.
Understanding some of the components that keep your central air conditioner or heat pump cooling efficiently can be helpful to a homeowner. Today, we’re going to discuss AC capacitors and the vital role this little part plays in the cooling of your home.
What is an AC Capacitor and How Does It Work?
An AC capacitor, also known as an HVAC capacitor, is a vital component of any central AC unit or heat pump. It’s a silver canister that looks somewhat like a battery. It’s a small part that plays a big role in cooling your home. If you were to look inside your outdoor unit, you would see a mass of wires connected to the canister.
Look But Don’t Touch
You can look but don’t touch an AC capacitor or the wiring. AC capacitors are dangerous, high-voltage components. Touching or mishandling one could lead to serious injury or death. Always consult an experienced and licensed HVAC technician if you’re experiencing problems with your air conditioner or heat pump’s cooling.
What Does a Capacitor Do?
The capacitor for your AC unit or heat pump provides energy to your cooling system’s motor to help it cool your home. The AC capacitor stores electrical energy and gives your AC unit or heat pump compressor motor an electrical jolt to start the motor when the thermostat indicates the need for cooling.
Once the air conditioner or heat pump compressor motor is running, the AC capacitor’s job isn’t done. The capacitor reduces its energy output but continues to supply a steady current of power to the motor until the cooling cycle finishes.
Types of AC Capacitors
There are two types of AC capacitors - the start capacitor and the run capacitor. In some systems, there are two AC capacitors. But in other cooling systems, there is a dual capacitor that handles both the start and run functions. It’s essentially one canister containing both the start capacitor and the run capacitor.
AC capacitors are measured in voltage and microfarads (MFD). Voltage measures how much electrical current is moving through the capacitor. The more voltage in your capacitor, the faster the electrical current moves throughout it.
Microfarads, meanwhile, describe how much electrical current the capacitor can store. Most capacitors range from 5-80 MFD. Capacitors with an MFD above 70 are starting capacitors.
Signs of a Bad AC Capacitor
The AC capacitor works hard, and may eventually fail. The average lifespan of an AC capacitor is 15 years, but it can be shorter if you run your AC more. In fact, capacitor replacement is one of the most common air conditioning repair tasks. Here are some signs you may have a bad AC capacitor:
The Unit Is Running but There’s No Cool Air Blowing
Is the AC running but not cooling? The capacitor may not be powering the compressor, so the unit isn’t getting enough refrigerant.
The Outside Unit Emits a Loud Humming Noise
Is the outside AC unit humming loudly? The unit will normally hum when it’s running. But if you notice a very loud sound, it can be another sign of a failed or failing capacitor.
The AC Unit Turns Off Randomly/Short Cycles
Is the AC short-cycling? If the AC unit randomly turns off, it’s short-cycling, or ending a cycle before it’s fully complete. This can be a sign the capacitor is failing.
The AC Unit Won’t Turn On at All
AC won’t turn on at all? Like all other AC problem symptoms, this one can be caused by a lot of things, but a failed capacitor is one of the possibilities.
There Is Smoke or a Burning Smell at the Outdoor Unit
Burning smell from the AC? This could also be a sign of a failed capacitor. You should immediately turn off the power to the unit and contact an HVAC company to schedule repairs.
If you’re having problems with your AC unit or heat pump cooling properly, visit our troubleshooting tips for help.
What Causes an AC Capacitor to Fail?
You know by now that the AC capacitor is one of the hardest-working components in your cooling system. Common reasons for the capacitor to fail include:
- Wear and tear over many years
- An extreme heat wave that keeps it running continuously
- Short circuit in the wiring
- Lightning strike
When it’s time to replace an AC capacitor, you should know that it’s not a cheap repair, but it’s not cost-prohibitive by any means. An average cost for this common AC repair is $100-$300, depending on the type of capacitor, where you live, and other factors.
How to Test a Capacitor
Since capacitors are high-voltage parts connected to electrical wiring, we don’t recommend that you test or try to replace a bad AC capacitor yourself. Leave that up to trained HVAC professionals who can test and diagnose a problem safely. They will know how to test a capacitor with a multimeter to tell if it is working properly or needs to be replaced.
However, testing may not be necessary to tell if the capacitor needs to be replaced. Visible signs of a failed capacitor include bulging, cracks, and oozing liquid.
Tips for Maintaining AC Capacitors
You can help prolong the life of your AC capacitor and the rest of your system by scheduling regular air conditioning and heat pump maintenance. During an AC tuneup, the HVAC technician will inspect and clean all parts of the cooling system, including the capacitors.
You should schedule cooling maintenance of your air conditioner or heat pump once a year - ideally in the spring before temperatures heat up. Read more maintenance tips to keep your system running at peak performance.
Your Local American Standard Dealer Can Help
A bad capacitor is one of the most common air conditioning repair issues homeowners face. Fortunately, AC capacitor replacement is a relatively straightforward and cost-effective repair. If a failed air conditioner capacitor is the only issue, replacing it can get your central air conditioning system or heat pump cooling properly again.
If your system is aging out or repairs are getting more and more costly, it may be time to start considering air conditioner replacement. Check out our Repair or Replace Guide for guidance.
If you do decide to replace your air conditioner or upgrade to a heat pump, know that American Standard’s outdoor units are designed to provide superior energy-efficient cooling and quiet, reliable operation. We’ve designed down to the smallest detail, from the most complex parts to the most basic features, like the cabinet and basepan.
Contact your local American Standard HVAC professional to schedule AC repair to get your home comfortable again. They can also make new product recommendations.
Anne Fonda, Content Writer
A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.
She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism.
When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.
Expert review by Kimberly Sexton, Senior Systems Engineer
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