AC Capacitor Ultimate Guide: Types, Cost and Replacement

An air conditioner capacitor is a small cylindrical container that is located in your outside AC condensing unit or heat pump. The capacitor stores energy until the energy is needed, then releases it to power the condenser fan motor and/or the compressor. It supplies a little extra “juice” for the unit at startup or to keep running without interruption. These functions are described below.

A capacitor for AC unit can cost anything from $5 to $35 for the part, depending on the brand you prefer and the type of capacitor needed.

In our comprehensive guide below, we explain what a capacitor does, how to tell when your capacitor is failing, how you can replace a bad capacitor, what types of AC capacitors are available, what factors go into the cost for a DIY or professional capacitor replacement, and more. 

Note: This guide is a response to the search query “capacitor for ac unit” and is not about a vehicle AC capacitor.

Article contents:

Capacitor Types

Capacitors are one of the most essential components for your AC system. There are two main types of capacitor for ac unit: an AC run capacitor and an AC start capacitor. A run capacitor comes in two subtypes:

Single Run Capacitor 

This capacitor starts the condenser fan motor and keeps it running. It does not require a start capacitor in order to function.  

Dual Run Capacitor

“Dual” is a key term here. The unit with this capacitor subtype uses both a start capacitor and a run capacitor. The start capacitor gives the initial push for the motor, disengaging once the fan is in motion. The run capacitor keeps the fan going and powers the compressor.

If you were to have a run capacitor and a start capacitor in front of you for a side-by-side comparison, you would notice that both a single run capacitor and a start capacitor have two terminals on top, while a dual run capacitor has three.

AC capacitor with diagram
AC capacitor

The number of terminals for each type of capacitor will never change.

A capacitor’s terminals are labeled “C” (sometimes “COM”) for “common,” “H” or “HERM” for “hermetic,” and “F” for “fan.” The C terminal connects the contactor to the capacitor, giving the capacitor power. The F terminal powers the condenser fan motor, and the H terminal powers the compressor.

Important note: the colors for each wire can be different from one AC appliance to another, but the placement of each wire will never change.

Causes and Signs of Bad Capacitors

There are a number of things that can cause your unit’s capacitor to fail:

  • Aging. No matter which capacitor(s) your unit uses, it is prone to losing its storage capabilities over time, eventually failing to hold an electrical charge - It wears out. 
  • Power surges. Since capacitors are delicate, a power surge—especially several surges over time—can easily destroy them.
  • Overheating. This could be from the high outside temperatures overwhelming the device, or it can be from internal heating in the unit itself. In other words, this failure might indicate there is something else wrong with your condenser unit.

How to Tell if AC Capacitor is Bad

While it can be difficult to determine if the AC capacitor is bad, there are signs that point to it:

The outside AC fan stops working. You will hear humming from the unit when this happens because the fan motor is trying to work but isn’t receiving the power it needs to do so.

Your outside AC condenser unit won’t turn on, but your inside air handler will. When this happens, your air handler will spew hot air in place of cold air. You may even find a start delay with the air handler.

The capacitor is expanding or bulging on top. This can sometimes look like a dome or even a mushroom top. 

Bad Capactor

Do I Have A Bad Capactor?

The oil inside the capacitor is leaking out along the sides.

The compressor stops working. This problem only occurs with dual run capacitors.

If you find yourself dealing with issues #1 or #2 above, you should know that you may not be dealing with a bad capacitor. There are other problems that can cause the fan to stop or the entire unit to shut down, which you can learn about in the PickHVAC FAQ guide called Outside AC Unit Not Running But Inside Is.

Capacitor Test

If the physical characteristics of the capacitor are normal - it isn’t leaking or misshapen - but you’re suspecting the capacitor is the issue, there is a way you can test the component to find out.

Put a thin but sturdy wooden stick through the grate that is shielding your unit’s fan and gently push the fan into motion. (Warning: Avoid using your fingers or conductive materials, such as metal, for this. Otherwise, you may be electrocuted, which will lead to serious injuries or fatality. You also don’t want your fingers in there if the fan whirls into motion.)

Single Run Capacitors: If the fan starts spinning on its own and your unit has a single run capacitor, then the capacitor is likely weak and near its way out. If the fan does not spin, the capacitor has likely failed, which could also mean damage to the fan motor.

Dual Run Capacitors: On the other hand, if the fan starts spinning and your unit uses a dual run capacitor, this could mean one of three possibilities:

  • Debris and/or dust is wedged inside the unit, preventing the fan axle or fan motor from performing.
  • The start capacitor is weak and will soon die.
  • The fan motor is damaged. The problem with this is that most homeowners don’t possess the tools or know-how to determine the exact cause of the issue. An HVAC technician will be able to assist in this scenario. A damaged fan motor could mean that the motor is the problem by itself, while the capacitor is fine. It could mean that both components are damaged and need replacing. You could even find your unit needing additional replacements and fixing, such as with the compressor.

Finally, if the fan does not spin and your unit has a dual run capacitor, then the run capacitor will need to be replaced. 

How to Replace AC Capacitor

Here are step by step run capacitor replacement instructions. Read them over, and if you have the tools and basic skills to test the capacitor, go for it. How to replace AC capacitor is pretty straightforward but with a few precautions. 

  1. Turn the power off before working on the unit. To do so, switch off the AC and furnace circuit breakers, then pull out the disconnect in the disconnect box located near the outside AC unit.
  2. Close the disconnect box lid as an extra precaution.
  3. Use a drill to remove the screws and take off the access panel to the capacitor.
  4. Use a multimeter to ensure the unit is fully powered off. You may have disconnected the power supply, but a unit can sometimes carry residual charge.
    1. If you don’t own a multimeter, you can buy one at your local Home Depot. For info on a clamp multimeter, see the third question in our “FAQ” section below.
    2. If you don’t know how to use the multimeter, refer to this video: https://www.youtube.com/watch?v=PBoOx8YzD_s.
  5. If you find a nest inside, or if there’s a lot of dust and debris, you’ll need to clean the area before applying the following steps. But be careful: messing with any coils can short out the unit.
  6. Make sure that your new capacitor is the same type as the one you are removing.
  7. If you have a dual run capacitor: When you applied the capacitor test by moving the fan, did the fan start up again? If so, you will only need to replace the start capacitor. If the fan did not move, you will only need to replace the run capacitor. (The run capacitor is typically gray/silver).
  8. Rub a pair of needle-nose pliers or screwdriver between the capacitor terminals to discharge residual voltage. Don’t remove the capacitor before you have done this. Note: Make sure the pliers have rubber or plastic handles rather than bare metal, so no charge gets conducted to your hand.
  9. Loosen the bracket holding the capacitor in place, then take the capacitor out of the bracket with wires attached.
  10. Take a picture of the capacitor with the wires still connected so that you remember where each wire goes later.
  11. Use pliers—not your fingers—to disconnect the wires.
  12. Install the new capacitor, plugging the wires in their appropriate terminals.  

For a visual tutorial on this process, watch this video:

Quick Quiz on the video - was that a single run or dual run capacitor?

When Buying a New Capacitor

Before purchasing a new capacitor for your AC unit, you’ll need to consider the following:

  • Which type of capacitor (i.e., start or run) do you need?
  • What’s the shape of the original capacitor?
  • How much energy storage should your capacitor have?

Capacitor Type Needed

Using the capacitor test, you can determine which of the capacitor types you’ll need to replace.

As a reminder:

  • Owners of a single run capacitor unit: If the condenser fan did not spin or began to spin slowly when you applied the capacitor test, you will need to replace the capacitor.
  • Owners of a dual run capacitor unit: If the fan spins when applying the test, you will likely have to replace the start capacitor. If the fan does not spin, you’ll need to replace the run capacitor.

Shape

Residential central AC units or heat pumps can require round or oval-shaped capacitors, which both vary in length. Before purchasing a new capacitor, what is the shape of your current one?

  • Round run capacitor example:
  • Oval capacitor example:
Oval capacitor example

While you can switch a round capacitor for an oval capacitor or vice-versa, it is best to stick with what you already have. There isn’t a lot of wiggle room in the capacitor’s location, so you may not be able to fit an oval-shaped capacitor in the round capacitor’s place. Shape ultimately isn’t as important, if it fits, as the capacitor’s specifications which follow.

Energy Storage

An easy way to determine how much energy your replacement capacitor will need for your particular AC appliance is by referring to the owner’s manual. If you’re no longer in possession of the manual, you may be able to find a PDF copy online, or you could call the AC appliance manufacturer to ask what your specific AC unit requires.

If you look at your capacitor, you’ll find a list of values labeled on it. The ones you should especially know:

  • Capacitance
  • Tolerance rating
  • Voltage rating

Capacitance (capacity): A capacitor’s capacitance is how much energy it can store. The capacitance is measured in microFarads (µF), which will come in a variety of sizes depending on which type of capacitor you need.

Start capacitors range from 70µF to 200µF, while run capacitors go from 1.5µF to 70µF (with a few exceptions being as high as 100µF). You’ll need to make sure the new capacitor has the exact capacitance your unit requires. For example, if your old run capacitor is 50µF, your new one should be, as well.

Run capacitors are sometimes labeled with two capacitance values—a large value and a small value (45µF/5µF, for example). Whenever you come across this situation, note that the small value is related to the fan motor.

Mismatching capacitors by capacitance will likely damage your AC appliance. An undersized capacitor, for instance, will overheat the fan motor and compressor by forcing them to work harder, while an oversized capacitor will overcharge them.

Tolerance: The tolerance rating is represented by a percentage. It is difficult for manufacturers to figure out the capacitor’s true capacitance, so the capacitance has a range. If, for example, you own a 50µF run capacitor with a tolerance rating of +/- 6%, this means your capacitor is still usable if its capacitance value is still between 44µF and 56µF. You will need to replace the capacitor if its capacitance dips below this range, or if you find its capacitance is higher than 56µF.

Voltage: The voltage rating is how many volts (V) can pass through the capacitor. It’s good to note that AC units and heat pumps typically have a minimum voltage rating of 370VAC. Newer condenser units commonly require capacitors with 440VAC.

Just like mismatching capacitance values, if the new capacitor has a voltage rating that’s too high or too low than what is needed, the capacitor will fail. You can base what you need off the voltage value on your bad capacitor, but if you have never replaced the capacitor personally, it’s possible that the HVAC professional put the wrong size capacitor in your unit. For a precise understanding of what voltage rating you’ll need, you’ll have to determine what the fan motor or compressor requires.

Prices - How Much Does an AC Capacitor Cost?

The cost of your project is contingent on these factors:

  • The capacitor brand you use 
  • DIY vs. professional installation
  • Capacitor size
  • Possible miscellaneous expenses

Choice of Capacitor Brand

We’ve been asked several times before if the new capacitor has to be the same brand as the AC unit or heat pump. Luckily, the answer is, No. Your purchase can be from any brand you prefer, so long as the capacitor you buy follows the guidelines we listed in the “When Looking for a New Capacitor” section.

Lennox, Goodman, and Carrier are all reliable brands for HVAC parts. A Lennox AC run capacitor will range from $9 to $25 depending on the voltage, capacitance, and subtype (single or dual run). Lennox start capacitors begin at $50 and cap off around $80.

A Goodman AC run capacitor ranges from $4 to $32 depending on voltage, capacitance, and subtype. Unfortunately, Goodman does not sell start capacitors.

A Carrier AC run capacitor begins at $5 and cap off around $32 depending on voltage, capacitance, and subtype. Carrier’s start capacitors begin as low as $14 and go as high as $100.

Note - You might not find a capacitor labeled as a Goodman AC capacitor or Carrier AC capacitor. Many ACs can be fitted with capacitors from other manufacturers as long as the part has the right specifications as the old capacitor. 

DIY vs. Professional AC Capacitor Replacement

Replacing a capacitor on your own should cost somewhere between $5 and $200. The large discrepancy between the numbers is based on a few factors:

  • Capacitor type. A run capacitor can be $5 or $30, while a start capacitor can be as much as $100. The cost of your DIY project is mostly reliant on which capacitor you’ll need.
  • Capacitor Brand. Some brands are cheaper than others, and generally, you get what you pay for.
  • Tools. Do you have a screwdriver or drill? Do you own a multimeter? If you are missing these tools, they will raise the price quite a bit. A multimeter like this one is a handy tool to have, and other tools. It’s affordable and quite useful when diagnosing electrical issues around the house.

Keep in mind that while replacing a bad capacitor can be DIY, it is not a task for the inexperienced. Not only can the job lead to serious, if not fatal, electrical injuries, but a non-professional might not be able to detect if the unit is experiencing other issues such as a damaged fan motor or compressor.

For these reasons, we suggest calling a reliable HVAC professional to do the job for you.

If you decide to hire a professional, you can expect the cost to be somewhere between $125 to $375, according to our 2020 AC Repair Guide. These prices include the cost for the capacitor and an hour or less of labor.

The expense for professional help may vary on the cost of living in your area and on whether the repair is made during the company’s usual business hours or as an after-hours emergency.

Possible Miscellaneous Expenses

In the case your capacitor ruins your fan motor or compressor, replacing a fan motor can take at least two hours of labor, which will be a $200 to $700 expense depending on the damages. Compressors can be repaired, but the most cost-effective option for long-term satisfaction would be to replace the damaged compressor, which will require one to three hours of labor for $1,200 to $2,500. When repairs get into that range and the AC is already 10+ years old, your money might be better spent on a new AC condenser unit

Where to Buy an AC Capacitor Online and Locally

If you haven’t purchased a capacitor before, you may be at a loss on where to buy AC capacitor online or locally.

For online purchases, capacitors can be found on Amazon for any price between $5 and $35, depending on the brand. Lennox, Goodman, and Carrier capacitors are available via Amazon, although you can also find other brands, such as Genteq and MaxRun, with the right specs for a range of brands including Rheem, Ruud, Trane, Heil, etc. 

Repair Clinic has a superb HVAC parts website with a wide variety of available products.

  • If you’re looking for a Lennox AC capacitor, refer to this link.
  • For a Goodman AC capacitor, go here.
  • For a Carrier AC capacitor, go here.

If you are a Home Depot enthusiast, you can also find a few options on their website.

Unfortunately, if you rely on Home Depot for most of your home improvement purchases, you should know that the company doesn’t carry capacitors in stores. You may find that your local store is the exception, but the company reserves its capacitors for online shopping.

If you’re a homeowner who prefers in-store shopping, you can go to an HVAC parts store. Don’t know where to find one near you? This website lists over 70 HVAC stores and their locations across the country. For a faster search, type your specific city, state, or ZIP code at the top.

Helpful Tips to Know When Hiring a Professional 

If you decide to hire a professional, here are some things to keep in mind:

  1. Make sure to get written cost estimates from at least two contractors. This way, you will be able to compare costs and job quality, getting the most for your buck.
  2. Tell each professional that he is competing for your job. If contractors understand they are competing, they will be less likely to make installation shortcuts or overprice you for their services.
  3. It is worth researching if a company is licensed, insured, and has the most experience with AC unit installation. Hiring someone without these qualifications could mean more AC trouble in the future.

If you don’t have the time to research company qualifications, we can help! See our free estimate service, which prescreens HVAC contractors for experience, licensing, and insurance. There is no cost to filling out a form or any obligation to accept an estimate, and because these contractors already know they’re competing for your project, they will be less likely to gouge you.

FAQ

1. Can I run my AC unit on a weak AC capacitor?

Unfortunately, no. If you have to push start the fan every time, for example, well, that’s going to get old fast and lead to greater damage to the condenser unit (outside AC unit).

Like a battery, capacitors can’t be fixed, only replaced. A weak capacitor may do its job for the most part, but by leaving it in, you will be forcing the fan motor to put in more effort to compensate for the capacitor. This will eventually overwork the motor, causing it to fail.

If your unit uses a dual run capacitor, you also risk damaging the compressor, which will cost you over $1,000. (See compressor price range in “Prices” section above.)

You should replace the weak capacitor as soon as you can.

2. Is there any way to keep my start and/or run capacitors from failing?

No, all capacitors go out eventually. But keep in mind they are fairly inexpensive, and experienced DIYers can make the repair. 

This said, you can ensure your capacitor(s) has a longer lifespan by regularly cleaning the condenser unit. In other words, you can

  • Cut the surrounding grass to keep it from growing too high around the wires.
  • Get rid of any debris in and outside the unit. The fan can especially get messy with leaves, dirt, and sticks.
  • Prevent insects or rodents from making homes inside the unit. You’ll also do well to check the unit’s wiring from time to time since rodents are prone to chewing them.

3. Do I always have to disconnect the run capacitor when I want to test it with a multimeter?

It depends on what you prefer.

If your unit isn’t working and you’re trying to see if your run capacitor is the problem, there is nothing wrong with removing the capacitor. However, for homeowners who perform regular maintenance checks on their units, constantly removing the capacitor can get annoying.

You can test your run capacitor under load (which is to say, when the AC unit or heat pump is on) by using a clamp multimeter. Using a non-clamp multimeter can lead to serious, if not fatal, injuries.

If you do not own this kind of multimeter, you can easily find one on Amazon (see link below). But before you purchase a device, you’ll want to make sure you understand the differences between the four clamp multimeter types, as you may find one type is more user-friendly than another.

To distinguish the four types:

To purchase a clamp multimeter.

You can test your capacitor under load by doing the following:

  1. Take off the access panel. Note your capacitor’s voltage (VAC), tolerance (+/- %), and capacitance values (µ), as labeled on the capacitor’s body.
  2. Clamp the multimeter around the single wire that connects the HERM terminal on the run capacitor to the start terminal on the compressor. Set the rotary switch on amperes (amps) to find the value of the current in the wire.
  3. Multiply the amps by the universal constant, 2,652. (Example: 8 amps x 2,652 = 21,216).
    Note: Some contractors use 2,650 or 2,653 as the universal constant. These are not technically wrong, but 2,652 will give you the most accurate results.
  4. Set the rotary switch on voltage. Place the meter leads on the C and HERM terminals to measure the voltage across the capacitor.
  5. Take the number you previously calculated and divide it by the voltage rating you see on your multimeter. The quotient is the capacitors present capacitance. (Example: 21,216 / 367VAC = 57.8µF)
  6. If the quotient is lower than the capacitor’s labeled capacitance value, does it fit within the tolerance range? If not, then your capacitor is weak and will need replacing. (Example: The capacitor capacitance value we received is 57.8, and the capacitor’s labeled capacitance is 60µF with a +/- 3% tolerance rating. 57.8µF falls within three values of 60, so it’s still usable.)

For a visual tutorial of this process, see this video:

4. Can I use a start capacitor in place of a run capacitor?

No. Start capacitors and run capacitors have too many differences to be interchangeable. Using a start capacitor in place of a run capacitor would short out your AC system and would likely lead to the fan motor and/or compressor malfunctioning.

5. How long can I expect my capacitor to last?

A capacitor is built to last the lifespan of the AC unit or heat pump, which is to say 15-20 years.

This is liable to fluctuate, however, depending on

  • The ambient temperature
  • The number of times the unit or heat pump receives maintenance
  • The frequency at which the AC system is used
  • How old the capacitor is to begin with
  • How often you experience power surges
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