Your air conditioner unit may look like a simple box outside, but there are several important components inside it that are doing very technical work. One of the most important, and one that most commonly fails, is the A/C capacitor.
Capacitors are the small electrical components that give motors the jump start they need to begin turning. You can think of them as tiny batteries that store energy and release it with a quick burst the exact moment the A/C needs to start the fan motor or the compressor. Without that extra jolt of stored energy, the motor will not start smoothly – and if something goes wrong, doesn’t start at all.
What Exactly Is a Capacitor and What Does It Do?
Your A/C unit doesn’t just need power – it needs power that is controlled and regulated. The capacitor is the part that is responsible for sending the correct electrical charge at the exact moment the compressor or fan needs to start. That surge is the core element that allows the motor to start quickly and then settle back into normal run mode.
Most systems have a separate capacitor for the compressor and the fan motor. These components are small and cylindrical in shape, and tucked inside the outdoor unit. They are relatively inexpensive compared to most other HVAC parts, but when they fail, they can immediately stop the entire system from running.
How Often Does a Capacitor Wear Out?
Air conditioner capacitors are considered “normal wear” items. They are not considered permanent components of the unit. In a mild or average climate, many capacitors can last up to five to seven years. In Arizona, and especially in our extreme summer conditions, it’s not uncommon to see a capacitor fail sooner, as they are continually firing under a heavy load.
When the outdoor temperature exceeds 100°, the A/C cycles more frequently and is running under higher electrical stress. That constant strain shortens the lifespan of the capacitor. So yes, it is true that A/C capacitors are one of the most commonly replaced parts in Phoenix. It’s one of the top five repair calls that HVAC techs get called out for during summer.
Why Do Capacitors Fail?
Capacitors fail due to a combination of factors including heat, age, electrical stress, and excessive cycling. Inside every capacitor is a set of plates and dielectric materials that are required to store energy. Over time, these important materials will break down. The hotter the environmental conditions, the faster the breakdown happens.
If the A/C is rapidly cycling on and off throughout the day, the capacitor is constantly in a state of recharging and discharging, which accelerates its wear. Other factors such as electrical spikes, brownouts, or voltage drops from the power grid can also cause damage to capacitors.
In some cases, the capacitor itself may have been built with lower-quality materials, which causes it to fail prematurely. It’s also common for capacitor housings to swell or bulge before they fail, which is a sign the internal elements of the component are breaking down.
What Does It Look Like When a Capacitor Is Failing?
Signs of failing capacitor often appear through during start-up. You may hear a humming noise or buzzing sound when the system tries to kick on. In some cases, the outdoor fan might not spin up on start. The system may try to start repeatedly but fail to fully engage.
In other instances, your lights in your home might flicker briefly when the system attempts to power on. And other times, the system will just blow warm air because the compressor didn’t start successfully. These are the common, tell-tale signs that the capacitor is struggling and may be headed for failure.
When Is Capacitor Replacement the Right Move?
It makes sense to replace the capacitor the moment it tests outside of the proper electrical tolerance range. Most HVAC technicians use a meter that enables them to measure microfarads according to the rating printed on the capacitor. If the measurement is outside of the acceptable percentage of that rating, it should be replaced.
This is a relatively simple and inexpensive repair, especially when comparing against the cost of replacing the compressor or motors. The important thing to keep in mind is to not wait until that capacitor completely dies. A stressed capacitor will force the other components to work even harder. Allowing a capacitor to continue to run in a weakened state eventually causes the compressor and/or fan motor to start overheating, which can lead to a far greater expense.
Replacement is also the right move if the capacitor has any visible signs of bulging, leaking, corrosion, or swelling. Once the internal components begin to deform, failure of the part is not far behind. Replacing a capacitor will proactively protect the major components of your A/C unit and reduce the chance that the system will fail to cool your family off during the hottest part of the day.
The Final Word
Capacitor failure is one of the most common A/C and normal repairs, particularly in Arizona, and discovering and addressing it early can prevent more serious mechanical failures. Capacitors are relatively low-cost, but high-impact components that keep the motors in your system running smoothly.
When capacitors weaken or fail, the system will lose its ability to start properly and the strain will begin the lead to the premature wear of more expensive parts. Paying attention to unusual signs such as start-up noises, hesitation, or intermittent system operation, is the best way to get ahead of the damage that leads to a more expensive repair later.
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