The Function of an AC Capacitor
Air conditioners require a burst of energy to start their motors, often more than your circuit can supply on its own. That’s where the capacitor comes in. It stores an electrical charge and then releases it to “jump start” key components such as the compressor, outdoor fan motor, and indoor blower motor.
Depending on the system, there may be one capacitor powering all three motors, or separate capacitors for each. Either way, without a functioning capacitor, the motors won’t kick on.
Signs That Your Capacitor Needs Replaced
Capacitors wear out naturally over time and can also be damaged by power surges. When one begins to fail, you’ll usually notice warning signs:
- Clicking sounds: A failing capacitor often makes a distinct clicking noise, and if ignored, it can cause the motor to burn out.
- Hard starting: The motor struggles to start, then quickly shuts off again.
- Humming or buzzing: If the capacitor is completely dead, the motor won’t start at all and will just hum when trying to turn on.
If you notice any of these symptoms, it’s time to replace the capacitor before it causes further damage.
Steps for Removing an AC Capacitor
Replacing a capacitor is possible for a homeowner, but it requires extreme caution. Capacitors store a large amount of electricity and can deliver a dangerous shock if not handled properly. To safely discharge it, use an insulated screwdriver and place the blade across the two terminals. This will release the stored charge.
Always cut the power before you begin. First, turn your thermostat to “OFF.” Next, shut off electricity to the outdoor unit. Many systems have a disconnect box nearby—either a breaker switch or a block fuse. If not, flip the double-pole 240-volt breaker labeled “air conditioner” in your home’s electrical panel. If it isn’t labeled, you may need to shut off the main breaker.
After confirming the power is off, remove the access panel on the outdoor unit. The capacitor is a metal can-shaped cylinder with wires attached. Discharge it with your screwdriver, then carefully label each wire so you’ll know exactly where to reconnect them later.
Dual capacitors that power both the outdoor unit and blower fan usually have three terminals labeled F (fan), C (common), and H (hermetic/compressor). Single capacitors will only have two. Once the wires are labeled, you can disconnect and remove the capacitor.
Bring the old part to the store to ensure you buy an exact match. The replacement must meet the same specifications in tolerance, capacitance, and load voltage—otherwise, it won’t work properly. Even if the new part looks slightly different, it will work as long as the ratings match.
Installing the New AC Capacitor
Once you have the correct part, secure the new capacitor in place with the mounting strap. If the strap is damaged, replace it as well. Reconnect the wires to the correct terminals, making sure each one is in the right spot.
Before closing the unit back up, restore power at the breaker or fuse and test your system. Set your thermostat to “cool” and lower the temperature so the AC turns on.
- If the system runs normally, the job is done.
- If it doesn’t start, double-check your wiring, discharge the capacitor again, and reconnect as needed.
- If it’s wired correctly but still won’t run, either the wrong capacitor was installed or another issue is preventing startup—such as a burned-out motor. At that point, a licensed HVAC technician will need to inspect the system.
Expert AC Inspections and Repairs
If you’re unsure about replacing a capacitor yourself, the professionals at Blue Best Plumbing, Heating, Air, & Generators are here to help. Our certified HVAC technicians can quickly diagnose capacitor issues and inspect your entire system to catch any other problems affecting performance.
Our team has more than two decades of experience providing air conditioning and heating services to residents of Bountiful and the rest of the Greater Salt Lake City area, and we also specialize in indoor air quality services. We also provide indoor air quality services to keep your home healthier and more comfortable.
Whether you need a quick capacitor replacement or a full AC system upgrade, call Blue Best Plumbing, Heating, Air, & Generators today.
