When an air conditioner breaks down during the summer, one of the most common culprits is a failed capacitor. Here's what you need to know about these critical components, why they fail, and how to protect your system.
What Is a Capacitor and What Does It Do?
Think of a capacitor like a rechargeable battery — it stores up electrical energy so it can deliver a quick burst of power to a motor when needed. There are two types found in HVAC systems:
- Start capacitors provide the extra voltage needed to get the compressor or fan motor running at the start of each cycle.
- Run capacitors supply a continuous stream of energy to keep those motors running throughout the cycle.
Heat pumps and air conditioners typically use a dual run capacitor connected to both the compressor and the fan motor. Furnaces use a single run capacitor connected to the blower motor. Without a functioning capacitor, your system simply won't run properly — or at all.
Why Do Capacitors Fail?
1. Overheating
Capacitors are sensitive to heat. On a hot summer day, roof-mounted units can reach temperatures exceeding 150°F. Add a system that's working overtime to keep up with the heat, and you have the perfect recipe for an overheated capacitor. You can help by setting your thermostat a few degrees higher on the hottest days, and using reflective blinds on east- and west-facing windows to reduce heat gain inside the home.
2. Power Surges
A lightning strike can instantly fry your HVAC's electrical system — but even smaller surges cause damage over time. Fluctuations in the electrical grid, large appliances cycling on and off, and power restoration after an outage can all weaken capacitors. An HVAC surge protector is a relatively inexpensive investment that can save you a much more costly repair down the road.
3. Age
Capacitors wear out. Like any electrical component, their ability to store and release energy diminishes over time. This is simply inevitable — but catching it early makes all the difference.
Warning Signs of a Failing Capacitor
- The compressor struggles to start, then quickly shuts off
- The system rapidly cycles on and off
- Humming or clicking noises from the unit
- The AC runs but doesn't cool effectively
- The unit won't start at all
Why You Should Never Ignore a Failing Capacitor
A capacitor replacement — caught early — is one of the least expensive HVAC repairs there is. But if you let the system keep running with a failing capacitor, the connected motor will overheat and burn out. Instead of a simple capacitor swap, you could be looking at a new fan motor, a new compressor, or even an entirely new system.
The takeaway: if your AC is acting strangely this summer, call us sooner rather than later. A quick diagnosis now can save you thousands.