Run Capacitor in AC Unit: Start Capacitor vs Run Capacitor (2024)

Table of contents
What does a run capacitor do on an air conditioner
How does run capacitorwork?

How to test a run capacitor?
The difference between startcapacitor and run capacitor

A Capacitor is an electronic component that stores an electrical charge and releases a current when needed. It is separated by a dielectric between two conductors, creating an electric field that can store electrical charges. The capacity of a capacitor determines the amount of charge it can store, and the unit is usually expressed in farads. In air conditioner, capacitors play an important role in providing and storing energy. Specifically, air conditioner typically uses two different types of capacitor: Start capacitor and Run capacitor. Start capacitor is used to help the motor generate sufficient torque when starting. Run capacitor is used for the continuous operation of the motor. These two different types of capacitors play different roles in AC unit, but both are designed to provide and regulate current to support the start and operation of the motor. They play an important role in the normal operation of air conditioner, ensuring the performance and efficiency of the motor.

This article discusses the run capacitor in detail, and compares the run capacitor with the Start Capacitor.


What does a run capacitor do on an air conditioner

What is Run Capacitor

A Run Capacitor is a capacitor used during the operation of a motor in air conditioner. It is a capacitor that operates continuously, providing additional current and energy to increase the torque and power factor of the motor.


The role of the Run Capacitor for ac unit

1.Provide additional current: The Run Capacitor meets the needs of the motor by storing charge and releasing the stored charge when the motor requires additional current.

2.Increase the turning moment: The Run Capacitor provides an additional turning moment to enable the motor to overcome load and inertia and maintain stable operation.

3.Improve power factor: Improve the power factor of the motor to convert electrical energy into mechanical energy more efficiently, improving the efficiency of the system.

4.Balance current: The Run Capacitor can help balance the phase current of the motor to ensure normal operation of the motor and reduce the risk of overload and unbalance.

5.Stable voltage: The operating capacitor absorbs transient voltage fluctuations in the circuit, thereby maintaining voltage stability. This is very important to ensure the normal operation of the circuit.

6.Reduce current fluctuations: The operating capacitor reduces the current fluctuations in the circuit, thereby reducing the loss of the circuit. This is very beneficial for improving the efficiency of the entire system and extending the service life of the equipment.

7.Filtering effect: The running capacitor also has a filtering effect, which filters out high-frequency noise in the circuit, thereby improving the performance of the circuit.

How does run capacitorwork?


A Run Capacitor works by storing an electrical charge and releasing a current when needed. When the motor is started, the Run Capacitor creates an electric field between the power line and the motor. During the operation of the motor, the Run Capacitor continuously provides additional current and energy.

Specifically, when the motor starts running, the current on the power line passes through the Run Capacitor. The Run Capacitor stores a portion of the charge and releases a current according to the demand for the charge. This released current is superimposed on the operating current of the motor, providing additional energy and increasing the torque and power factor of the motor.

The capacity and voltage level of the Run Capacitor are selected according to the motor and application requirements. The correct capacity and voltage level ensures that the Run Capacitor can provide the appropriate current and energy to support the proper operation of the motor.

What happens when a run capacitor goes bad & cause

Impact of Run Capacitor damage and possible problems

1.Startup problems: A damaged Run Capacitor may cause the motor to have difficulty starting or fail to start at all. Because the Run Capacitor cannot provide enough additional current and energy, the motor may encounter starting resistance and be unable to overcome load and inertia.

2.Unstable operation of the motor: A damaged Run Capacitor may cause unstable operation of the motor. It may not be able to provide the additional current and energy required, causing the motor to lose torque or experience speed fluctuations during operation.

3.Motor overheating: When the Run Capacitor is damaged, the motor may become over-loaded because it is unable to obtain additional torque and support for rotation. This can cause the motor to overheat and damage windings or other critical components.

4.Reduced power efficiency: A damaged Run Capacitor cannot improve the power factor of the motor, resulting in a decrease in power conversion efficiency. This can lead to wasted energy and higher electricity bills.

5.Increased risk of motor damage: Continuing to Run the motor with a damaged Run Capacitor may result in further damage. Damaged capacitors can cause motor current imbalance, overheating, and other electrical problems, eventually leading to complete motor damage.

In summary, when the Run Capacitor is damaged, it may result in start-up problems, unstable motor operation, overheating of the motor, decreased energy efficiency, and an increased risk of motor damage. Therefore, it is recommended to replace the damaged Run Capacitor in time to ensure the normal operation of the motor and protect its reliability. It is not recommended to continue using a Run Capacitor with damage, as it may further damage the motor and other system components.

Is it safeto run AC with bad capacitor?

Using a damaged Run Capacitor may cause the motor to fail to operate properly or cause other faults during operation. In addition, a damaged Run Capacitor is unable to provide the additional current and energy required, potentially resulting in reduced performance and wasted energy for the motor.

To ensure normal operation of the motor, prevent further damage, and improve system reliability, you are advised to replace the damaged Run Capacitor.

How to test a run capacitor?

Steps

1.Power off: Before performing any tests, make sure to turn off the power and disconnect the wires associated with the Run Capacitor.

2.Discharge: Using an insulated screwdriver, short circuit the lead of the Run Capacitor to ensure that the charge in the capacitor is fully released. This avoids the risk of electric shock if a live lead is touched.

4.Test run capacitorwith multimeter: Select the appropriate capacitance range on the multimeter, generally choosing a higher range, such as 200μF or higher. Select a range based on the nominal capacitance of the Run Capacitor to be tested.

5.Connect test leads: Connect the test leads of the multimeter to the two leads of the Run Capacitor. Make sure the lead is in good contact with the lead and is not loose or disconnected.

6.Observe and record the Capacitor: Observe and record the capacitor of the Run Capacitor based on the Settings of the multimeter. If the capacitance value is close to the nominal value, then the Run Capacitor is usually normal. If the capacitance value is significantly lower than the nominal value or appears as infinity ("OL"), then the Run Capacitor may have been damaged.

RELATED: How to Test Capacitor with Multimeter

Matters needing attention

1.Before testing the Run Capacitor, make sure to disconnect from the power supply safely and discharge to avoid the risk of shock if you touch a live lead.

2.Use an insulated screwdriver or other insulating tool to discharge the charge in the Run Capacitor.

3.When connecting test leads, ensure that the lead is in good contact with the lead and is not loose or disconnected to obtain accurate measurement results.

4.See the nominal Capacitor of the Run Capacitor to determine whether the measurement result is normal.

5.If the capacitance of the Run Capacitor is significantly lower than the nominal value or infinity is displayed, the Run Capacitor may be damaged, and you are advised to replace it.

If you are unsure about testing with a multimeter, or need more in-depth diagnosis and repair, consult a professional electrical technician or repairman.

The difference between startcapacitor and run capacitor

A start capacitor is a capacitor used to help start an electric motor. It usually has a high capacitance value to provide additional starting current. Starting capacitors are connected in parallel to the motor's starting loop to provide additional phase shift and current spikes to help the motor overcome starting resistance and inertia.

A run capacitor is a capacitor used in the operation of an electric motor. It usually has a low capacitance value and is mainly used to improve the power factor and efficiency of the motor. The operating capacitors are connected in parallel to the motor's operating loop, allowing the motor to operate more efficiently, reduce reactive power, and improve the power factor by introducing additional current phase shifts.


Capacitance value: start capacitor typically have high capacitance values, usually between tens of microfads (μF) and hundreds of microfads (μF). Operating capacitors have low capacitance values, typically ranging from a few micrometers (μF) to tens of micrometers (μF).

Function: The main function of the start capacitor is to provide additional starting current and phase shift to help the motor overcome starting resistance and inertia to achieve reliable starting. The main function of the runcapacitor is to improve the power factor and efficiency of the motor, reduce the reactive power loss, and improve the operating efficiency of the motor.

Connection mode: The start capacitor is usually connected in parallel with the starting circuit of the motor and plays a role when the motor starts. The run capacitor is connected in parallel with the operating circuit of the motor and continues to function during the operation of the motor.

Purpose: start capacitor ismainly used to help motors start, especially for motors that need to overcome high starting resistance or inertia, such as air conditioning compressors. Run capacitors are mainly used to improve the operating efficiency and power factor of motors, and reduce energy waste, and are commonly found in applications such as fans, pumps, and compressors.

In summary, start capacitor isused to help the motor start, providing additional starting current and phase shift; The runcapacitor is used to improve the power factor and efficiency of the motor, reduce the reactive power loss, and improve the operating efficiency of the motor. They have obvious differences in capacitance value, function, connection mode and use.

Also read: How to Safely Discharge an AC Capacitor

Run Capacitor in AC Unit: Start Capacitor vs Run Capacitor (2024)

FAQs

Run Capacitor in AC Unit: Start Capacitor vs Run Capacitor? ›

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.

How do I know if I need a run capacitor or start capacitor? ›

However, there are signs that might alert you to the problem. If the compressor on the outside unit of your air conditioner has trouble starting or cycles quickly on and off, the start capacitor may be failing. If the air conditioner repeatedly starts and stops, the run capacitor might be the culprit.

Can I use a start capacitor as a run capacitor? ›

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.

What is the difference between a start capacitor and a run capacitor on an air compressor? ›

In summary, start capacitor is used to help the motor start, providing additional starting current and phase shift; The run capacitor is used to improve the power factor and efficiency of the motor, reduce the reactive power loss, and improve the operating efficiency of the motor.

What are the advantages of capacitor run over capacitor start? ›

Start Capacitor: Provides a high starting torque by creating a large phase shift during the start-up. Run Capacitor: Maintains the phase shift during normal operation, ensuring smooth and efficient running.

What are the symptoms of a bad run start capacitor? ›

If the start capacitor malfunctions or wears out, it usually prevents the HVAC unit or the blower from turning on. A bad run capacitor won't prevent the unit from starting, but it can lead to the unit shutting down prematurely, overheating, or making more noise than usual.

Can AC run without start capacitor? ›

Most of the motors in your air conditioner can't run without a good capacitor.

What happens if you use the wrong start capacitor? ›

If the wrong run capacitor is installed, the motor will not have an even magnetic field. This will cause the rotor to hesitate at those spots that are uneven. This hesitation will cause the motor to become noisy, increase energy consumption, cause performance to drop, and cause the motor to overheat.

Do all AC motors need a start capacitor? ›

In case of DC Motors, both conventional (Brushed) and modern (BLDC) do not require a capacitor in their operation. In case of AC Induction Motors, the single phase motors need a capacitor if they are split phase induction motors or capacitor start or capacitor-start—capacitor-run induction motors.

Can I replace a start capacitor with a higher uF? ›

A slightly higher capacitance value will result in slightly more power available from the motor if the load requires it. But a capacitor WAY BIGGER than 30uf (100uf, for example) might cause the motor to draw too much current and make it overheat.

Will a compressor run with a bad run capacitor? ›

In most cases, this indicates that the AC capacitor is bad. The capacitor is responsible for providing power to the AC compressor, so when it fails, the compressor can't run properly. As a result, your AC unit won't be able to cool your home effectively.

Do all AC units have a start and run capacitor? ›

Depending on how your HVAC system is built, there may be two single capacitors or one dual capacitor in your outdoor unit. Systems requiring two single capacitors need a start capacitor and run capacitor to function properly.

What are the disadvantages of a capacitor start capacitor run motor? ›

The disadvantages of capacitor motor include the following.
  • The cost of the paper capacitor used in the motor is expensive and also its size is larger as compared to an electrolytic capacitor with the same ratings.
  • It has less starting torque.

Can I use a start capacitor instead of a run capacitor? ›

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.

What is the difference between starting capacitor and running capacitor? ›

While the start capacitor provides an initial electrical push to the motor helping it to start, the run capacitor helps in maintaining that start and charge. Note: Working principle of an electric or DC motor is that a current carrying conductor will produce a magnetic field around it.

What is a capacitor start capacitor run motor used for? ›

This arrangement is known as a capacitor-start, capacitor-run motor. Capacitor induction motors are widely used for heavy-duty applications requiring high starting torque. Examples are refrigerator compressors, pumps, and conveyors.

Will a motor run with a bad start capacitor? ›

If your HVAC capacitor is bad, the motor will run at higher amplification, run backwards or stop running altogether. Investing in the health of your HVAC system will save you time and money including your HVAC tune-up in Sacramento.

When should a run capacitor be replaced? ›

The lifespan of AC capacitors varies from unit to unit, but generally speaking, they should be tested and replaced every 20 years or so. If your air conditioner unit is older than 20 years, it's a good idea to have it checked by a professional AC technician who can inspect the capacitor and replace it if necessary.

How can you test a run capacitor? ›

Testing the run capacitor with a multimeter. You can use an analog Ohm meter to test the capacitor's ability to store and release an electrical charge. You can also test the component to determine if it has the proper capacitance rating by measuring the microfarads present in the capacitor.

References

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