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What is Air Conditioner Capacitor and How does it Work?

Author: Apogeeweb Date: 17 Jul 2021  278

safety capacitor


With the improvement of living standards, all kinds of electrical equipment have gradually entered thousands of households. In many electrical appliances, air conditioning is also essential. However, many consumers are ignorant of the working principles of air conditioners and the principles of cooling and heating. In fact, for the operation of the air conditioner, the key to its operation is the air conditioner capacitor. Without this part, the air conditioner cannot operate normally. So what exactly is an air conditioner capacitor? What are the structural characteristics of this part?


Ⅰ What is Air Conditioner Capacitor

Ⅱ Types of Air Conditioner Capacitor

  2.1 Electrolytic Capacitor  

  2.2 Safety Capacitor 

  2.3 Ceramic Capacitor 

  2.4 Capacitors for Starting and Running Air Conditioner

Ⅲ Structure Characteristic of Air Conditioner Capacitor

Ⅳ Working Principle of Air Conditioner Capacitor

Ⅴ Main Reasons for the Failure of Air Conditioner Capacitor

  5.1 Heat Exposure 

  5.2 Voltage Capacity 

  5.3 Shorter Lifespan

Ⅵ The Detection of Air Conditioner Capacitor

Ⅶ Methods to Repair And Replace Air Conditioner Capacitor

Ⅷ Frequently Asked Questions about Air Conditioner Capacitor

Ⅰ What is Air Conditioner Capacitor

The so-called air conditioner capacitors are also called aluminum electrolytic capacitors. It is a capacitor made of an aluminum cylinder as the negative electrode, which is filled with liquid electrolyte, and inserted into a curved aluminum strip as the positive electrode. The core of the air conditioner capacitor is made by overlapping and winding anode aluminum foil, liner paper impregnated with electrolyte, cathode aluminum foil, and natural oxide film. After the core is immersed in the electrolyte, it is sealed with an aluminum shell and a plastic cover to form an air conditioner capacitor. Generally, there is a plastic sleeve outside the aluminum shell of the air conditioner capacitor.

what is air conditioner capacitor

So-called air conditioner capacitiors

Also, it's a little cylindrical container within your air conditioner that stores and distributes energy. When you turn on your air conditioner, it demands more power than your home's electrical system can provide—this is where the capacitor comes in. Moreover, the AC capacitor is a component within the outdoor condensing unit of an air conditioner or heat pump. It delivers power to the motor driving the air conditioning system. The capacitor delivers initial energy burst to turn the system on when it's time for a cooling cycle.)


Ⅱ Types of Air Conditioner Capacitor

2.1 Electrolytic Capacitor 

This capacitor for air conditioner has polarity and leads labeled with + or - marks. It is typically used to smoothen the DC voltage after it has been rectified by diodes. They aided in reducing the ripples in the DC supply. The smaller the ripple, the larger the capacitance of the capacitor employed. This use can be seen in a simple linear power supply with a step-down transformer.

2.2 Safety Capacitor

Safety capacitors are commonly used in the inverter control circuit of an air conditioner. They can be classified into X or Y types and used in the circuit's live parts always be careful when dealing with these capacitors as some charge on them may cause shock even when the power supply has been cut off.

safety capacitor picture

Safety Capacitor Picture

Good design should have bleeding resistors to remove the charge from the device after the air conditioner has been switched off. Ensure proper certification marks such as VDE, UL and CE markings are present on the bodies of the capacitors before using them.


Together with inductor coils, these capacitors are used to reduce the harmonics generated from the rapid switching of the AC power supply by the insulated gate bipolar transistors (IGBT).

2.3 Ceramic Capacitor 

Ceramic capacitors are used as bypass capacitors to bypass the high-frequency content of a circuit. They could be placed parallel to the DC power intake of integrated circuits to bypass certain high frequencies noise in the circuit that may have an adverse effect on the sensitive circuitry.


As the more transformerless power supply is becoming common today due to its better efficiency and smaller space, you will see many surface mount capacitors being used in multilayer printed circuit boards. These capacitors and inductor coils are used to reduce the harmonics, which are generated from the rapid switching of the AC power supply by the insulated gate bipolar transistors (IGBT).

2.4 Capacitors for Starting and Running Air Conditioner

These capacitors are commonly used in single-phase electric motors. START capacitor is used to alter the phase difference between a capacitor-start motor's START and RUN windings. This difference resulted in the generation of a starting torque capable of starting the motor with a full load connected to it.

start and running capacitor

 Start and Running Capacitor

The RUN cap. is used to further adjust the phase difference between the two windings, resulting in even more beginning torque. The connections in the motor are identified by marks on the single-phase compressor. The designations are R (connected to the RUN winding), S (connected to the START winding), and C (connected to the CUT winding) (common of the two windings).

Ⅲ Structure Characteristic of Air Conditioner Capacitor

1) The working medium of the air conditioner capacitor is to form a very thin layer of aluminum oxide (Al2O3) on the surface of the aluminum foil through anodization. This oxide dielectric layer and the anode of the capacitor are combined into a complete system, and the two are interdependent. The electrodes and dielectrics of what we usually call capacitors are independent of each other.


2) The anode aluminum foil and cathode aluminum foil of air conditioner capacitors are usually corroded aluminum foil, and the actual surface area is much larger than its apparent surface area. It is one reason why air conditioner capacitors usually have large capacitance. Due to the use of aluminum foil with many fine etched holes, the liquid electrolyte is usually needed to more effectively use its actual electrode area.

aluminum foil of air conditioner capacitor

The Structure of  Airconditioner Capacitors



3) The negative foil acts as an electrical lead in the air conditioner capacitor. Because the electrolyte as the cathode of the air conditioner capacitor cannot be directly connected to the external circuit, an electrical path must be formed through another metal electrode and other parts of the circuit.


4) Since the dielectric oxide film of the air conditioner capacitor is obtained by anodic oxidation, and its thickness is proportional to the voltage applied by the anodic oxidation, in principle, the thickness of the dielectric layer of the air conditioner capacitor can be artificially and accurately controlled.


It is precisely because of the structure characteristics and functions of the air conditioner capacitor that the air conditioner can operate normally. It should be noted that the capacitor should be checked for short circuit, open circuit and leakage before it is installed in the circuit, and its capacitance value should be checked. When installing, make it easy to see the capacitor type, capacity, withstand voltage and other symbols for verification.


The above points are related introductions to the structure characteristics of air conditioner capacitors. In fact, for air conditioner capacitors, it is not just used in air-conditioning. But there are many applications, such as air conditioning inverters, color TVs, displays, LED lights, energy-saving lamps and so on. Relatively speaking, the scope of application of air conditioner capacitors is usually in the field of household appliances.

Ⅳ Working Principle of Air Conditioner Capacitor

The capacitor is a key component to start the air conditioner motor. Most air conditioners on the market now use capacitors to start the air conditioner and take into account the operation. The damage of the capacitor will cause the compressor start current to rise too quickly, automatically turn on the protection mode to stop or fail to start the compressor, which will cause the air conditioner to fail to operate normally or automatically power off during the startup process. When the air conditioner is powered on, the capacitor acts as conduction to help the compressor start normally.


The capacitor gathers and stores energy while your air conditioner is running; in other words, it functions similarly to a rechargeable battery. That way, when your air conditioner requires a large burst of energy, the capacitor can supply it and keep everything working smoothly. The compressor (or compressors, depending on your air conditioner) powers the air conditioner's compressor, blower motor, and fan motor, which all rely on the compressor to stay operating and cold air flowing through your home.

Ⅴ Main Reasons for the Failure of Air Conditioner Capacitor

A capacitor experiences significant strain over its lifetime and using an air conditioner more frequently than typical increases this strain. Most capacitors are designed to last approximately twenty years under ideal conditions, although ideal conditions are not usually met. There are three major causes of failure for most capacitors:

This vedio shows that how to tell a AC Capacitor is bad !

5.1 Heat Exposure

Heat exposure is a term used to describe the condition of being exposed to heat.
While air conditioners are designed to keep you cool in hot weather, the hotter the environment, the more likely your capacitor will fail. Overheating the machine might cause harm and limit its lifespan. Keeping your air conditioner covered and well ventilated is an important aspect of reducing the risks of high temperatures in Houston.

5.2 Voltage Capacity

There are several air conditioner capacitors for various AC models, each with its voltage rating. The higher the voltage of a capacitor, the more expensive the part, so it may be tempting to replace it with a lower level capacitor. This, however, places a significantly greater demand on the capacitor, reducing its lifespan.

5.3 Shorter Lifespan

Again, most capacitors have a lifespan of roughly twenty years, but that also means they are only useful in certain situations. Older capacitors will be less capable, and higher-than-average AC consumption, as well as having a capacitor with malfunctioning parts, will limit its lifespan.


One of the most serious issues with an AC capacitor failure is that it might cause harm to other components that it powers. Fans can wear out, and electric connections can be damaged—if you spot a problem with the capacitor, replace it as soon as possible to avoid extra maintenance needs and expenditures.


Ⅵ The Detection of Air Conditioner Capacitor

Method 1: Use 220V alternating current to connect directly, you can connect one pole first, and touch the other capacitor pin with another power cord. If there is an obvious small spark when touched, you can be sure that the capacitor is charged, which means that the capacitor is not broken.


Method 2: Pointer multimeter, you can also use the digital meter to measure capacitance. If you use a pointer multimeter, generally use the R × 1K gear, and connect the test leads to the two poles of the capacitor respectively. At this time, the pointer of the multimeter will swing and then slowly return to or near the zero position. Such a capacitor is good. The larger the capacity of the capacitor, the longer the charging time, and the slower the pointer swings in the 00 direction. If it is connected, the resistance value displayed by the pointer does not move, it is bad.

Detection of Air Conditioner Capacitor

The methods of dectecting a airconditioner capacitor

Method 3: Check with a digital multimeter. Set the digital multimeter to an appropriate resistance range. The red and black test leads respectively touch the two poles of the capacitor under test. At this time, the display value will gradually increase from 0 until the overflow symbol "1" is displayed. If 0 is always displayed, it means that the capacitor is short-circuited. If it always shows overflow, it may be an open circuit between the capacitors, or the selected resistance file is not suitable.


The principle of selecting the resistance gear is: when the capacitor is large, the low resistance gear should be used; when the capacitor has a small capacity, the high resistance gear should be selected.


Ⅶ Methods to Repair And Replace Air Conditioner Capacitor

When you've established that your capacitor needs to be replaced, you have a few options. Because it is similar to a battery, the method is as simple as swapping it out for a new one. However, it is a bit more involved than simply removing the old capacitor and replacing it, so don't try it yourself if you aren't comfortable handling the parts.

There are various tips on how to replace a capacitor on your own, however here are some fundamentals to remember:


  • Find the right replacement capacitor. The capacitor should have a voltage and capacitance level on it, and you need to match that in your replacement. Writing down that and the make and model of your air conditioner can help the type of capacitor you need.
  • Power down your air conditioner before starting any fixes. It may sound like common sense, but it’s still vital. Working with high-electricity machinery can be dangerous without proper safety.
  • Discharge the capacitor. Even with your air conditioner turned off, the capacitor still has a significant amount of energy stored inside (that’s it is a job, after all). You need to discharge that energy so as not to cause damage to yourself during handling or after disposal. Make sure to wear proper safety equipment as well.
  • Take notes. Either draw a diagram of how your capacitor is connected or take several pictures to aid in the reconnection process.

Be aware of capacitor differences.·B If you’ve selected the same type of capacitor as your old one, this won’t be as much of an issue. However, some capacitors have different labels for the connections you need, so be aware of where these need to reattach so that you don’t have additional troubles.

Ⅷ Frequently Asked Questions about Air Conditioner Capacitor

1. What does a capacitor do for an air conditioner?

The main job of capacitors is to store electrons to provide start-up energy for your air conditioner, they build up a charge when electricity runs through them by swapping electrons between the two conductive plates inside.


2. How much does it cost to replace a capacitor on an air conditioner?

The average HVAC capacitor cost is around $170. Prices generally range between $120 and $250, including professional installation. Branded units are more expensive, costing upwards of $400 or more. The price you pay depends on the brand, model, voltage and the labor required for installation.


3. How long does an AC capacitor last?

The life expectancy of the air conditioner capacitor lies between 10-20 years. However, various factors, such as heat exposure, may tamper with their lifespan. If your capacitor is tiny or was built with the wrong parts, it may not live long.


4. Why is AC running but not cooling?

Condenser Unit is Blocked
If your air conditioner is running, but not lowering temperatures inside, one issue could be a blocked or clogged condenser coil. When operating correctly, the condenser fan draws air into the outdoor unit through the condenser coil to pull heat energy out of your home.


5. Can I replace the AC capacitor myself?

Yes, you can. It could be a capacitor, or it could be a compressor. Since capacitors are cheap, it may be worth a try to see for yourself if that's it, if not you will need a technician. There is really no “DIY” fix when it comes to repairing or replacing a capacitor.


6. How do I know what capacitor to get for my AC?

Multiply the full load amps by 2,650. Divide this number by the supply voltage. The full load amps and the supply voltage can be found in the owner's manual. The resulting number is the MicroFarad of the capacitor you need.


7. Do air conditioner capacitors get weak?

Power surges can cause a capacitor to fail, too.

Obviously, a lightning strike from a summer thunderstorm can overload and burn out your HVAC's electrical system., Also weaker power surges can cause damage to capacitors over time. Those weaker surges can be caused by fluctuations in the electrical grid.


8. Should I turn off AC if it's not cooling?

If your ac is still not cooling, there is one more thing you need to do. This is very important. TURN IT OFF and call your HVAC service provider to assist you. We always tell our customers to turn off an ac that is not cooling properly.


9. What does a bad capacitor look like?

Well, bad caps typically have a domed or swollen top. Sometimes really bad caps can leak their electrolyte out of themselves too. Then you may see this brown crust around the capacitor, or perhaps on it. It often looks somewhat like a dried coffee stain.

Ordering & Quality

Photo Mfr. Part # Company Description Package PDF Qty Pricing
EEU-FC1J101 EEU-FC1J101 Company:Panasonic Remark:Aluminum Electrolytic Capacitors - Radial Leaded 100uF 63V Package:N/A
In Stock:On Order
1+: $0.51000
10+: $0.39000
2500+: $0.13200
T491X476K035AT T491X476K035AT Company:KEMET Remark:Tantalum Capacitors - Solid SMD 35V 47uF 2917 10% ESR=600mOhms Package:N/A
In Stock:On Order
1+: $2.65000
10+: $2.05000
100+: $1.62000
500+: $1.08000
1000+: $0.96900
2500+: $0.90000
10000+: $0.86500
T491B476K010AT T491B476K010AT Company:KEMET Remark:Tantalum Capacitors - Solid SMD 10V 47UF 1311 10% ESR=1 Ohms Package:N/A
In Stock:On Order
1+: $0.57000
10+: $0.31300
100+: $0.22000
500+: $0.20200
1000+: $0.17200
2000+: $0.13700
10000+: $0.13300
24000+: $0.12900
50000+: $0.12500
C0603X104K5RACTU C0603X104K5RACTU Company:KEMET Remark:Multilayer Ceramic Capacitors MLCC - SMD/SMT 50V 0.1uF 0603 X7R 0.1 Package:N/A
In Stock:On Order
1+: $0.19000
10+: $0.07700
100+: $0.06500
500+: $0.04400
1000+: $0.03900
4000+: $0.03300
8000+: $0.02900
24000+: $0.02800
48000+: $0.02700

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