The start capacitor may be the problem if the motor is energized and makes a humming sound but does not rotate or rotates slowly. The run capacitor may be the problem if the motor starts but runs at a higher than stated current load (amps) and overheats.
There are two different types of capacitors: start capacitors and run capacitors. Although the concept behind both devices is similar in the way they charge energy, they serve different purposes, and cannot be interchanged.
Motor start and run capacitors are used in single-phase AC induction motors. Such motors are used whenever a single-phase power supply is more practical than a three-phase power supply, such as in domestic appliances. They are not as efficient as three-phase AC induction motors, however.
Capacitors with ratings above 70 microfarad (uF) are starting capacitors. Run capacitors are designed for continuous duty, and are energized the entire time the motor is running. Single phase electric motors need a capacitor to energize a second phase winding. This is why sizing is so critical.
If it will not run at full speed, is noisy, overheats or hesitates while rotating, the run capacitor has failed.
In some cases, you can tell that a capacitor is bad without testing. Common indicators of this include a capacitor that looks expanded or bloated, signs of leaking dialectic fluid, an oil-soaked top cap, or any other physical issues.
The capacitor is one of the parts you should expect to replace at some point in your AC's lifetime. While your AC itself could last for 15 years, the capacitor won't last that long. It might make it five years before you need to replace the capacitor. In some systems, there are multiple capacitors.
A start capacitor is only used in the motor circuit for a second or two when it first starts to turn. Once the motor is up to speed, the start capacitor disconnects and is not used again until the next time the motor starts. If the start capacitor fails, then the motor will not be able to begin turning.
The simple answer is “No.”
This is not to imply bigger is better, because a capacitor that is too large can cause energy consumption to rise. In both instances, be it too large or too small, the life of the motor will be shortened due to overheated motor windings.
For AC capacitor replacement, anticipate spending between $150 and $400, depending on the capacitor's type and accessibility. A bad AC capacitor is a fairly minor repair, and most HVAC technicians will recommend a repair rather than replacing the unit when the capacitor is the problem.
Always discharge the capacitors with a discharging tool, which can be found online. Never touch a capacitor until you have done so.
The start capacitor creates a current to voltage lag in the separate start windings of the motor. The current builds up slowly, and the armature has an opportunity to begin rotating with the field of current. A run capacitor uses the charge in the dielectric to boost the current which provides power to the motor.
Overheating is a primary cause of a failed start capacitor. Start capacitors are not designed to dissipate the heat associated with continuous operation; they are designed to stay in the circuit only momentarily while the motor is starting. If a start capacitor stays in the circuit too long, it will overheat and fail.
There are two common types of motor capacitors, start capacitor and run capacitor (including a dual run capacitor). Motor capacitors are used with single-phase electric motors that are in turn used to drive air conditioners, hot tub/jacuzzi spa pumps, powered gates, large fans or forced-air heat furnaces for example.
The motor or compressor being powered by the capacitor will have trouble running smoothly or may not run at all. You can often tell that a capacitor has failed because the casing will bulge or leak. If you observe any bulging or leaking, the capacitor will require immediate replacement.
Capacitors can fail due to a number of reasons and when they fail it can lead to short-circuit, damage to the circuit and sometimes even explosion.
The capacitance and voltage ratings would have to match the original start capacitor specification. A start capacitor can never be used as a run capacitor, because it cannot not handle current continuously.
A faulty capacitor – whether it's the wrong size, blown, or damaged – can be the root cause of your motor hum. Solution: Test and replace any faulty capacitors. Both the start and run capacitors are usually located on the exterior of the motor housing, often in dedicated metal or plastic casings.
Although your unit may continue to run, it is not wise to continue using the air conditioner before replacing a failing capacitor as it can lead to compressor failure and fan motor issues as well as system failure.
One of the most common signs of a failing AC capacitor is an overly warm home. Without this component, the cooling cycle won't start and indoor temperatures won't go down. Other signs of capacitor problems include: Loud humming sounds coming from the AC condenser.
While your AC will still work with a bad capacitor, it will struggle to function correctly. Eventually, the system will stop working altogether. Extended use can cause further damage internally. We recommend contacting a professional to handle the repairs so that you don't risk any damage to your air conditioning.
Excessive heat generation in the motor or capacitor area can signal a malfunctioning capacitor. Overheating is often caused by increased electrical resistance due to capacitor failure, leading to elevated temperatures that can damage the motor windings and surrounding components.