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How to Replace an AC Capacitor

Author: Apogeeweb
Date: 19 May 2022
ac capacitor cost



Ⅰ What is an AC Capacitor? 

1.1 AC Capacitor Circuit

1.2 What does the AC Capacitor do?

Ⅱ Why do AC Capacitors Fail?

2.1 Signs of a bad AC Capacitor

2.2 Reasons for AC Capacitor Problems

2.3 Effects of a bad AC Capacitor

Ⅲ How to test an AC Capacitor

Ⅳ Difference Between AC & DC Capacitors

Ⅴ AC Capacitor Replacement Cost

Ⅵ How to Choose a AC Capacitor Replacement

Ⅶ How to Replace an AC Capacitor

Ⅷ Frequently Asked Questions about AC Capacitor

1. What Happens When an AC Capacitor Fails? 

2. What to do When the Capacitor Breaks Down?

3. How long does AC Capacitor last?

4. Can I replace my AC capacitor myself ?

5. How to maximize the life of AC capacitor ?

6. Will My AC Unit Still Work with a Bad AC Capacitor?

7. What is the difference between a start capacitor and a run capacitor?


The cost of your AC capacitor will be determined by the cost of the unit plus the labor necessary for installation. When it's time to begin a new cycle of cold air, your ac capacitor stores energy to provide a boost to the unit. If the capacitor fails, your system may fail when it is most needed (which is always, of course). Don't worry, this is a straightforward and inexpensive fix. This essay will educate you on AC.

How to Test Motor Start and Motor Run AC Capacitor of ac fan and compressor

 What is an AC Capacitor? 

An AC capacitor is a small electrical component that stores energy and provides a power surge. In this situation, the capacitor stores energy until your thermostat sends a signal indicating that your air conditioner must be turned on.

At this point, the capacitor releases a burst of energy to supply a beginning current to your AC unit's compressor.

This is necessary since the ordinary power supplied to your AC is insufficient to start the motor on its own. This rapid boost is required for the motor to start. Once the engine has started, the power from your house will suffice to keep it running.

The AC capacitor itself resembles a battery, with two or three wires protruding from the end. Some colored bands around the body of the capacitor will also be utilized to identify how much power it is rated for.

1.1 AC Capacitor Circuit

The capacitor in the purely capacitive circuit above is linked directly across the AC supply voltage. As the supply voltage rises and falls, the capacitor charges and discharges in proportion. We know that the charging current is proportional to the rate of change of the voltage across the plates, with the rate of change being largest when the supply voltage crosses over from its positive half cycle to its negative half cycle, or vice versa, at points 0o and 180o along with the sine wave.

As a result, when the AC sine wave crosses over at its maximum positive peak ( +VMAX ) and its minimum negative peak ( -VMAX ), the voltage rate of change is the slowest. The sinusoidal voltage is constant at these two points in the cycle, hence its rate of change is 0, so DV/DT is zero, resulting in zero current change within the capacitor. When DV/DT = 0, the capacitor serves as an open circuit, therefore I = 0, as illustrated below.


1.2 What does the AC Capacitor do

A capacitor in a central air conditioning system is intended to provide a power increase at the start of each system cycle. This is required to get the air conditioner's fan to run at maximum speed. When the fan motor reaches its maximum speed, the capacitor stops working until the system is restarted.

 Why do AC Capacitors Fail?

Capacitors are a component of your air conditioner or heat pump system; they will eventually wear out and need to be replaced. Overheating is the most prevalent cause of air conditioner capacitor failure. On visual inspection, the ac capacitor will be enlarged and may even rupture due to the pressure caused by overheating. This is a dead giveaway that your capacitor is faulty.

Here are a few reasons why an ac capacitor can overheat.

  1. Extended or abnormal run-time: a heatwave or an inadequately charged refrigerant level in your air conditioner.
  2. Compressor Age: Just like people, compressors take more energy to start up as they age. This can overwork a capacitor and signal the impending failure of a compressor.
  3. Lightning or Power Surge: Power grid spikes or fluctuations, which are frequently caused by lightning strikes, can wreak havoc on a capacitor.
  4. Capacitor Age: The quality of capacitors manufactured nowadays is simply not what it once was. A capacitor's average life expectancy is only 8-12 years.


2.1 Signs of a bad AC Capacitor

When an AC capacitor needs to be replaced, you'll notice a variety of symptoms, including:

  • Your air conditioner is taking too long to start chilling.
  • Your air conditioner shuts down on its own.
  • Your air conditioner does not operate at all.
  • Your air conditioner makes a noise but does not provide chilly air.
  • Your air conditioner is making a buzzing or humming sound.
  • You smell a burning odor or see smoke coming from your unit.
  • Your utility bills are inexplicably high.

An AC unit's capacitor might fail due to age and regular wear and tear, an overheated system, an unknown short circuit, lightning strikes or power surges, or excessively hot temperatures.

2.2 Reasons for AC Capacitor Problems

There are numerous causes for an air conditioner's capacitor to fail. While only a professional heating and cooling specialist can establish the exact cause of capacitor breakdown in your specific air conditioning machine, the following are some of the most typical reasons that this part fails:

  • Physical damage to the capacitor, such as when a piece of debris strikes the unit.
  • Inadequate voltage or current flowing through the capacitor.
  • The unit has overheated.
  • Wear and tear caused by aging.

2.3 Effects of a bad AC Capacitor

The rising warmth inside your home is the first clue that your capacitor is no longer functioning properly. Other consequences may not be as obvious, but they can be harmful to your cooling system.

A faulty capacitor prevents the outside unit from performing its function, preventing the cooling process from taking place. Incorrect voltage might easily damage other sections of the machine.

Second, in an attempt to compensate for the failing capacitor, other components will begin to overwork. An rise in energy use may result in an unexpected increase in your monthly energy bill.

 How to test an AC Capacitor

As previously stated, the capacitor inside your heating and cooling system can be quite deadly if mistreated. As a result, it's advised to contact a local HVAC repair professional to test or replace your capacitor.

When the technician arrives, they will use a multimeter to calculate the capacitor's current, resistance, and voltage. In layman's words, they'll check to see if the capacitor is keeping the charge required to start and finish the cooling system. If the readings are faint or do not register at all, it is time to replace the AC capacitor.

Testing a capacitor is not suggested, even if you have a multimeter. While dozens of YouTube videos may make the procedure appear simple, it's advisable to avoid the DIY route and hire a professional. Capacitor testing is only possible after the power has been turned off, the wiring has been disconnected, and the voltage remaining in the capacitor has been drained.

It's a perilous task, and even after watching the most detailed how-to video, it's not safe to attempt. Use a professional.

 Difference Between AC & DC Capacitors

A capacitor is an electronic device made up of two plates of electrically conducting material separated by a non-conductive layer, known as an insulator. It is utilized in A/C (alternating current) and D/C (direct current) electrical applications and circuits to accomplish certain effects based on the capacitor's ability to store and discharge current.

Capacitors in DC Circuits


Electrolytic capacitors on circuit board

A capacitor's two plates, which are electrically insulated from each other, store energy in the form of capacitance. When DC is applied to a circuit consisting merely of resistance and capacitance, the capacitor charges to the applied voltage level. Because DC only flows in one direction, there is no more current flow once the capacitor is fully charged. This property enables capacitors to "block" DC flow.

Capacitors in AC Circuits

In alternating current circuits, the alternating current alternately charges the capacitor in one direction and then the other. As the plates discharge during the direction shift, the capacitor output current alternates in phase with the alternating current voltage. This is how capacitors are said to "pass" alternating current.

 AC Capacitor Replacement Cost

According to Home Advisor, the cost of replacing an AC capacitor ranges between $120 and $250, with the majority of fixes falling within the $170 range.

HVAC capacitor brand, model, and voltage are all factors that will influence the repair cost. The component itself typically costs between $9 to $45, while top-rated brand-name parts may be more expensive.

Labor and installation will consume the majority of your budget. Professional capacitor replacement often costs between $60 and $200. (By comparison, the average EMERGENCY ROOM VISIT costs $774, reinforcing our recommendation to hire a professional.) A technician should be able to do the job in approximately an hour.

Without an AC capacitor, your HVAC system would not function properly. This small but powerful component is responsible for keeping your home cool when summer temperatures climb. Schedule your seasonal HVAC maintenance with a skilled technician to guarantee that your capacitor and unit as a whole work optimally.

 How to Choose a AC Capacitor Replacement

You must choose the correct replacement if you are replacing your AC capacitor yourself. When it comes to ac capacitor replacement, the size and shape aren't important, but you will want to know two things: the voltage rating and the microfarads (F).

The voltage rating does not have to be the same as your present capacitor, but the microfarad must be the same. The voltage and microfarad are marked on your capacitor and may look like "35/5 F and 370V." When you go to your local home goods store, make a note of this, as well as the brand and model of your air conditioning system.

Finally, because capacitors are universal parts, form, size, brand, and other basic criteria are unimportant — just make sure to acquire the correct voltage and microfarad and you'll be fine.

 How to Replace an AC Capacitor


An AC Capacitor replacement can be purchased at a hardware store. Then it's time to put everything together:

Step 1 Turn off the power to your air conditioner at the breaker panel.
Step 2 To access the capacitor, unscrew the side panel of the condenser unit.
Step 3 Locate the capacitor and turn off the power.
Step 4 Remove the old capacitor and take note of how the wires are connected.
Step 5 Carefully unplug the wires from the three capacitor connectors labeled HERM, FAN, and C. Note or photograph which colored wires link to which connector for future reference.
Step 6 Install the replacement capacitor according to the instructions.
Step 7 Replace the side panel on the condenser unit.

 Frequently Asked Questions about AC Capacitor

1. What Happens When an AC Capacitor Fails? 

When an air conditioner capacitor fails repeatedly, the compressor motor in your system is unable to start. Your system may appear to be running, but the motor will never start, and you will not receive the chilly airflow you expect. In reality, while the motor tries and fails to start, you may hear a ticking or clicking sound.

2. What to do When the Capacitor Breaks Down?

When the air conditioner's capacitor fails, an AC capacitor repair is required. An expert AC service technician can determine whether the capacitor can be fixed or if it must be replaced. Our air conditioning repair technicians have new capacitors in the service vehicles they drive on all service runs, so you won't have to wait for this service if your capacitor needs to be replaced.

3. How long does AC Capacitor last?

The lifespan of HVAC capacitors varies slightly depending on the manufacturer and model. An AC capacitor has a 10-year average lifespan. SCHEDULE ROUTINE SEASONAL MAINTENANCE ON YOUR HEATING AND COOLING SYSTEM TO ENSURE YOU GET THE MOST OUT OF YOUR UNIT.

Annual maintenance on your HVAC system will allow a professional to detect any potential problems with the capacitor. Solving the problem before the part fails will save you the trouble of locating an emergency HVAC contractor and will keep you from experiencing unpleasant INDOOR TEMPERATURES in the heat of summer.

4. Can I replace my AC capacitor myself ?

You can't do it. An expert HVAC professional should be able to correctly remove your faulty capacitor and replace it with a new one, restoring your AC to normal operation.

5. How to maximize the life of AC capacitor ?

Avoid inconsistent voltage rating and exposing outdoor components to intense temperatures to extend the life of your ac capacitor. Regular checkups will also help to ensure the longevity of your equipment.

6. Will My AC Unit Still Work with a Bad AC Capacitor?

While your air conditioner will continue to operate, it will struggle to function properly. The system will eventually cease to function. Internal harm might be exacerbated by prolonged use.

We recommend hiring a professional to do the repairs so that your air conditioner is not damaged.

7. What is the difference between a start capacitor and a run capacitor?

A start capacitor, in essence, assists in starting the motor by providing a voltage boost at startup. A run capacitor keeps a motor going by producing a phase shift in the stators, allowing the rotor to "grab" and turn the next stator. When a run capacitor fails, this phase change does not occur, causing the motor to work harder, overheating and destroying the bearings.



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