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Signs of a Faulty AC Capacitor: Troubleshooting Guide

Signs of a Faulty AC Capacitor

The AC capacitor is an important element in the functioning of an air conditioning system. It serves as an electrical energy storage device that provides a boost of power to the compressor and fan motors, which are essential components of the AC system.


Without the AC capacitor, the compressor and fan motors would struggle to start, leading to potential damage due to excessive current draw and strain on the system. Moreover, the capacitor helps maintain a stable voltage supply, ensuring smooth and efficient operation of the air conditioning unit.

Identifying and addressing capacitor issues promptly in an air conditioning system is of utmost importance to prevent further damage and ensure the efficient performance of your AC unit. When a capacitor starts to fail or becomes faulty, it can lead to various problems in the AC system such as reduced efficiency, overheating, short cycling, and system failure. 


Table of contents:

  • What is an AC Capacitor? 
  • How Does an AC Capacitor Work?
  • Common Symptoms of a Bad AC Capacitor
  • AC Capacitor Troubleshooting and Diagnosis
  • AC Capacitor Replacement and Maintenance

What Is an AC Capacitor?

An AC capacitor is an electrical component commonly used in air conditioning systems and other HVAC (Heating, Ventilation, and Air Conditioning) equipment. It serves as an energy storage device, storing and releasing electrical energy to help the system’s motors start and run efficiently.

AC capacitors are typically of two types:

Start Capacitor: 

The start capacitor provides an extra burst of electrical energy to the compressor and fan motors during startup. When the air conditioner is turned on, these motors require a higher amount of electrical power to overcome the initial resistance and reach their operating speed. The start capacitor temporarily stores and delivers this energy, aiding in a smooth and quick startup.

Run Capacitor:

The run capacitor, as the name suggests, continues to provide electrical energy to the motors while the air conditioner is running. It helps to maintain a stable voltage supply to the motors, ensuring they operate efficiently and maintain their speed during the cooling cycle.

Both types of capacitors are essential for the proper functioning of an air conditioning system. They help prevent strain on the motors, reduce power consumption, and contribute to the overall efficiency and performance of the AC unit.

How Does an AC Capacitor Work?

An Air Conditioner capacitor works by storing and releasing electrical energy to assist the motors in an air conditioning system during startup and operation. When the air conditioner is turned on, the compressor and fan motors require a sudden surge of electrical energy to start running. The AC capacitor stores this energy and releases it when needed, allowing the motors to quickly reach their operating speed. 

Capacitors consist of two metal plates separated by an insulating material called a dielectric. This process stores electrical energy in the form of an electric field between the plates. When the capacitor discharges, it releases this stored energy to the motors.

It’s important to note that AC capacitors are designed to work with alternating current (AC) systems, which have continuously changing voltage polarities.

Common Symptoms of a Bad AC Capacitor

  • Weak or No Airflow

When the start capacitor, which provides the initial electrical boost during system startup, is faulty, it may fail to deliver enough energy to the compressor and fan motors. As a result, the motors may struggle to reach their operating speed, leading to weak or slow rotation of the fan blades and reduced airflow. In more severe cases, a completely failed start capacitor may prevent the motors from starting altogether, resulting in no airflow through the vents.

  • Inconsistent Cooling

If the run capacitor is faulty, it can affect the motor’s ability to maintain a consistent speed during the cooling cycle. The motor’s fluctuations can result in irregular cooling output, where the air conditioner may alternate between cooling effectively and not providing enough cooling.

The capacitor serves as an electrical energy storage device. It stores electrical charge and releases it when needed. When the air conditioner is switched on, the capacitor quickly charges up. Then, it provides an extra burst of electrical energy to the compressor, giving it the necessary kick to start running. This electrical boost helps the compressor overcome its initial inertia and reach its operating speed rapidly.

  • Frequent AC Cycling

Capacitor issues can cause the air conditioner to cycle on and off more frequently than usual. This phenomenon, known as short cycling, can put unnecessary stress on the system, increasing wear and tear.

  • Tripped Circuit Breaker

A faulty capacitor can cause the compressor and fan motors to draw excessive current from the electrical supply during startup. When the motors require more current than the circuit breaker’s rated capacity, the breaker detects this as an overload and trips to protect the electrical circuit from damage.

  • Strange Noises

A malfunctioning capacitor can produce unusual humming or buzzing noises when the air conditioner is running. These sounds may originate from the capacitor itself or the motor as it tries to compensate for the capacitor’s inadequacy.

AC Capacitor Troubleshooting and Diagnosis

AC capacitor troubleshooting and diagnosis involve identifying potential capacitor issues in an air conditioning system.

Before troubleshooting your AC capacitor ensure that you turn off the power and the necessary tools include screwdriver, multimeter, capacitance metre, capacitor discharge tool, insulated gloves and safety glasses, Replacement capacitor and flashlight.

Here are the steps to troubleshoot and diagnose problems with the AC capacitor: 

Visual Inspection: 

Start by inspecting the capacitor visually. Look for signs of any physical damage, such as bulging, leaking, or cracks in the capacitor’s casing. If you notice any of such issues, the capacitor is likely faulty and needs replacement. 

Check for Weak Airflow: 

If the air conditioner is running, but the airflow seems weak or inadequate, a faulty capacitor could be the cause. Weak airflow can result from the capacitor’s inability to start the fan motors properly.

Inspect Motor Operation: 

Observe the compressor and fan motor’s operation during startup. If the motors have difficulty starting, take longer to reach their speed, or stall, it may point to a faulty capacitor not providing the necessary electrical boost.

If you need any replacement parts for your air conditioner compressor, buy them from PartsHnC to ensure the high-quality. 

Capacitor Leakage Test: 

Some multimeters have a leakage current test feature. If available, use this feature to check for any leakage current, which could indicate a capacitor issue.

Check Motor Run Capacitor Terminals: 

If the air conditioning system has a motor run capacitor, check for loose or disconnected terminals, as these can also cause capacitor-related problems.

Capacitor Replacement: 

If you suspect or confirm a faulty capacitor, it’s crucial to replace it with a compatible and properly rated replacement.

If you are unsure or unfamiliar with troubleshooting and diagnosing the AC capacitor issues yourself, it’s best to seek the assistance of a qualified HVAC technician. 

AC Capacitor Replacement and Maintenance

AC capacitor replacement and maintenance are essential for ensuring the efficient and reliable operation of an air conditioning system. Here’s a guide on how to perform these tasks:

AC Capacitor Replacement:

Turn Off Power: Before attempting any capacitor replacement, turn off the power to the air conditioning system at the circuit breaker or disconnect the unit from the power source.

Discharge Capacitor: To discharge the old capacitor safely, use an insulated screwdriver with a rubber handle to short the terminals or use a capacitor discharge tool.

Take Pictures or Label Wires: Before removing the wires from the capacitor, take pictures or label them to ensure correct reconnection later.

Remove Old Capacitor: Use a screwdriver to remove any screws or clips securing the capacitor in place. Carefully detach the wires from the terminals.

Select Replacement Capacitor: Choose a replacement capacitor with the correct voltage and capacitance ratings. Install New Capacitor: Position the new capacitor in the same orientation as the old one. Reattach the wires to the appropriate terminals, ensuring they are securely fastened.

AC Capacitor Maintenance:

Regular Inspection: Periodically inspect the capacitor for any signs of physical damage, such as bulging, leaking, or cracks. 

Check Airflow and Cooling Performance: Monitor the airflow and cooling performance of the air conditioning system. If you notice a decrease in cooling efficiency or weak airflow, it might signal a capacitor issue.

Professional Maintenance: Schedule regular maintenance by a qualified HVAC technician. They can perform a thorough inspection of the capacitor and the entire air conditioning system, ensuring optimal performance and identifying potential problems before they escalate.

Remember that working with electrical components can be dangerous, so if you are uncertain about capacitor replacement or maintenance, it’s best to seek help from a qualified HVAC technician.

Follow our maintenance and troubleshooting tips to replace and maintain your AC capacitor. Check for the signs we have mentioned above to find out whether your capacitor is faulty or not. It is important to inspect your capacitor frequently to enhance the lifespan and for the efficient functionality of your Air conditioner. Get the help of a professional to replace your capacitor to avoid any issues later. 


  • How can I tell if my AC capacitor is faulty?

Look for the signs such as Frequent tripping, strange noises, not cooling, AC won’t start, Capacitor overheating, and bulging or leaking. These are the signs to look for to find out whether your AC Capacitor is faulty. 

  • Why is my air conditioner not blowing cold air?

If your air conditioner is not blowing cold air, then it might have the following issues:

  • Dirty air filters 
  • Refrigerant leak 
  • Faulty Compressor 
  • Faulty thermostat 
  • Blocked condenser unit 
  • Frozen evaporator coils 
  • Why does my AC keep turning on and off frequently?

If your AC keeps turning on and off frequently, the most common reasons could be:

  • Thermostat issues 
  • Dirty Air filters 
  • Frozen evaporator coils 
  • Oversized or Undersized AC 
  • Refrigerant leak 
  • Electrical issues 
  • Can a faulty capacitor affect the cooling of my AC?

Yes, a faulty capacitor can affect the cooling of your AC. The capacitor plays a crucial role in the proper functioning of the AC’s compressor and fan motors. It stores and releases electrical energy to help start the motors and keep them running smoothly. 

If the capacitor is faulty or failing, it can lead to several cooling-related issues such as reduced cooling performance, AC not starting, Frequent on/off cycling, warm air output and overheating. 

  • When should I replace my AC capacitor?

You should replace your AC capacitor when it starts showing signs of failure or becomes faulty. Replace your AC capacitor when you notice reduced cooling, frequent cycling, strange noises, bulging or leaking, or if your AC won’t start. It’s best to have a professional HVAC technician handle the replacement for safety and proper installation. Regular maintenance helps prevent sudden failures and extends your air conditioner’s life.

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