Your AC capacitor is a small but essential part. Several other AC components require the kick start a capacitor offers, such as the compressor, the fan motor, and the blower. If your capacitor goes bad or begins to wear out, your air conditioner won’t function properly or will cycle on and off many times in a continuous manner.
This article will look at the various types of AC capacitors and help you diagnose the problem, show you the different capacitor types, and help you replace your capacitor, including the cost to do so.
How AC Capacitors Work
A capacitor is a piece of electrical equipment that stores energy. It is connected to the condensing unit power supply (220V) and collects energy until it is needed. When the air conditioner needs to come on, the capacitor sends a high-voltage jolt (upwards of 400 to 600 volts) to the compressor, fan motor, and blower motor. They operate in a similar way to a car’s alternator.
Once the capacitor has started the components, your AC will come alive and begin blowing cold air. During the run cycle, the capacitor stores a new supply of energy while maintaining a constant flow to keep the other parts moving.
Most AC systems will have two capacitors. The primary capacitor in the condensing unit will power the compressor and the condenser fan motor. The secondary capacitor is generally smaller and will operate the blower motor in the evaporator unit.
Smaller AC units can run on a single capacitor while newer, larger systems will require three. Your system’s manual will tell you how many and which type of capacitors it requires.
Types of AC Capacitors
Generally speaking, there are two types of capacitors, start and run. Both types also have sub-types. Let’s take a look at the various types of AC capacitors.
A start capacitor produces the electricity needed to start an electromagnetic motor. A blower motor, for example, will require the jolt from a start capacitor to produce enough energy to begin rotation.
Start capacitors only engage long enough to get the motor running and then disengage; waiting until the next time they are needed. Each start capacitor has a capacitance measured in microfarads (µF), which we will cover further below. Microfarads are also labeled as MFD. This is important to note when looking for a new capacitor. MFD and µF are the same in this situation.
A Super Boost Capacitor/Turbo Capacitor isn’t technically a capacitor. They are also known as a hard start capacitor. The kit is designed to offer an even larger boost to get a motor running and will connect directly to the ports on the start capacitor. These are usually needed in rare situations when the compressor won’t start, or there is an electrical problem.
They are not designed to be installed and forgotten. Instead, they are made to help the AC system work to diagnose other problems or to get a new install up and going.
In your home AC, you will find a run capacitor is used more than a start capacitor.
A run capacitor operates whenever the system is on to help create the magnetic field that keeps coil motors moving.
There are two main sub-types of run capacitors.
A single-stage run capacitor will start and power a single motor or device. In our situation, this will be used to run the blower motor or the fan motor.
However, it is more likely that your condensing unit uses a dual-stage run capacitor.
You can tell because single-stage capacitors have two terminals on the top while a dual-stage capacitor has three.
Signs of a Bad AC Capacitor
The downside to an AC that isn’t functioning correctly is that several parts could be the underlying problem. For example, an AC not blowing cold air but otherwise operating fine could be the result of a bad compressor, a bad capacitor, or even a dirty air filter. Therefore the diagnosis is needed to determine the root cause of the issue. Here are some signs your capacitor is going bad or has failed.
AC Not Blowing Cold Air
As we mentioned above, this could be caused by another part of the system. An air conditioner not blowing cold air will only increase your energy bill. The run capacitor could be the culprit here, and if the air from your AC vents isn’t cold, check to see if the compressor is running.
If the compressor or the fan in the condensing unit is not running, they could be the problem. However, if both are not operating, it is most likely the run capacitor that is faulty.
High and Rising Energy Bills
When the HVAC system seems to be running fine, but you have noticed your energy bill increasing each month, your capacitor could be at fault. A capacitor doesn’t work one cycle and then fail the next. Instead, they get worse and worse as time goes on until they can no longer store enough power to start the system.
While they are still functional but going bad, the AC will run for shorter periods, causing it to cycle on more often. This increase in running times will cause your energy bill to spike.
A common sign of imminent failure is a light humming noise coming from your condensing unit, even when it isn’t running. You can remove the access panel to the compartment that houses the capacitor. If the humming gets louder, it is most likely the capacitor beginning to short out.
Old HVAC System
Age is another concern. A run capacitor has a life expectancy of about 15 to 20 years. However, areas that are warmer longer, like the southwest, will have a shorter life span for their capacitors because they are used and cycled more frequently. If your HVAC system has at least ten years of operation, the capacitor could be starting to fail.
AC Turns Off or On Its Own
We set our thermostats to a desired temperature for our comfort. The expectation is that when the temperature rises above this point, the air conditioner will come on. Once the set temperature is reached, the AC will shut off.
If your capacitor is bad or faulty, it can leak the stored electrons into the motors and cause them to turn on, even if the thermostat hasn’t opened the circuit yet. They can also cause the motors to shut off before the desired temperature is met.
AC Doesn’t Turn On Immediately
We also expect our systems to work. When the thermostat opens the circuit, the compressor and condenser fan should start up immediately. The blower motor in the evaporator unit may take some time to come on, though, so be aware.
Most blower motors are connected to a time delay switch that won’t allow the power to the motor for up to five minutes. However, if the AC is turned on, and the compressor takes more than 30 seconds to start, your capacitor could be to blame.
AC Won’t Turn On
If the above situation isn’t remedied, eventually, the capacitor will get to the point where it can’t power the system at all. When this happens, the AC won’t turn on at all. While this could be due to other factors, such as a worn-out compressor or a faulty thermostat, the most likely candidate is the capacitor.
Common Causes of AC Capacitor Failure
Just as there are many different signs that your capacitor is bad, there are also many different causes. The most common cause is age. As I mentioned earlier, the life expectancy of a run capacitor is about 20 years. The more an AC is used, the lower the age range becomes. However, if your capacitor is over ten years old and the system starts to act funny, the capacitor is the most common culprit.
Another cause of failure is heat. While it may sound counter-intuitive, a hot summer day can cause your capacitor to overheat. It is advised to keep your condensing unit in the shade during the hottest parts of the day.
As long as there is room around the unit for proper airflow, shade trees and shrubs can go a long way to prolonging the life of the electrical components inside the condenser, including the capacitor.
Finally, the voltage going to and from the capacitor must be within range. Each capacitor has a voltage rating, and if this is exceeded (or to some extent undervalued by a great deal), the capacitor can fail.
AC Capacitor Replacement & Repair Costs
Replacing your AC capacitor doesn’t have to cost an arm and a leg. As a DIY project (details further below), you will only pay for the capacitor itself. The price range will vary depending on a few factors, such as the brand, capacitance, and size of the capacitor you need. However, you should expect to pay between $5 and $30 for the part.
If you don’t want to take on the job yourself, you can hire a professional. According to Home Advisor, the average cost for a home visit, inspection of the system, and replacement of the capacitor will range from $90 to $400. This will include labor and parts. The entire job should take less than 30 minutes.
If you do hire out a professional, be sure to get a minimum of three quotes before you hire someone to do the job. You can check Angie’s List for recommendations of reliable professionals if you don’t have an electrician or HVAC repair specialist you know and trust.
Choosing Replacement Capacitors
When you have diagnosed the system and found the capacitor to blame, it is time to replace it. There are not parts of a capacitor that can be repaired, so once it fails or begins to fail, the only option is a replacement. Here are things to look for in a replacement capacitor.
Original Capacitor Voltage
Voltage is critical to the capacitor and the system. You must find one that has a voltage range capacity that matches your system. Each capacitor will have the voltage ratings printed on the side of the canister, as well as the packaging. If your capacitor is too old and the writing has worn off, your HVAC owner’s manual will tell you the proper voltage for your capacitors.
Original Capacitance Value
The capacitance value is measured in microfarads (µF). Run capacitors can range from 1.5 to 100 µF. A start capacitor will range from 70 up to 200 µF, and even higher for some commercial situations.
You must ensure that the microfarad rating is a match for your system. If it is not, the system may start by the motors will not have the proper magnetic shielding and will burn out or not run fast enough.
Frequency of Operation
Knowing how often you run your HVAC system on average will also help you determine which capacitor to purchase.
Overall Shape & Size of Capacitor
There are several sizes and shapes of capacitors, and getting the right one for your system is crucial. Primarily, a home AC will use a round or oval-shaped capacitor. These vary in length, but two to four inches is standard.
Before you purchase a new capacitor, you should look at the current one that is installed. It will be mounted to the inside of the access area of the condensing unit with a metal strap and a screw. There isn’t a lot of wiggle room inside this panel for larger capacitors. You can switch between oval and round, as long as you have the space for it.
You may need to replace the metal mounting strap for a longer piece if you switch to an oval-shaped capacitor, or to tighten the existing strap if going to the smaller cylindrical type.
Another factor to consider is the terminal type. A majority of homeowners won’t have to worry too much about this, as run capacitors use a male-end plug that slips into a female connector.
Some older models are the opposite, though, with the capacitor having the female leads and the wires using the male terminators. You will have to look at your capacitor to determine which style your unit has.
AC Capacitor Replacement Products
To get you started with your replacement research, I have compiled several brands, sizes, and types of capacitors for you to choose from. Remember that your capacitor must fit your system in size, voltage, and range.
Special note: While some run capacitors are rated and branded for a specific use, you do not have to stick to a particular brand. Just because a capacitor is a direct replacement for a Trane, for example, doesn’t mean it won’t work in a Goodman unit. As long as the voltage and MFD ratings are the same, the capacitor will work just fine.
To read the ratings, there are two numbers to be on the lookout for. All capacitors will have the MFD rating range. This will appear as two numbers split by a forward slash or sometimes a positive and negative symbol. For example, the Carrier capacitor, first on the list below, has an MFD of 45/5. This means it produces 45 µF with a variance of +5.
The second number after the slash is the variable in change. It shows how much discrepancy there is between the lowest and highest output. In this case, the 45 µF can be as low as 40 or as high as 50. If your capacitor rating is between 40 and 50, this capacitor will work for you.
1. Carrier 45/5 Dual Run Capacitor – Round
This model is a direct replacement for most Carrier models. Before you purchase, you should double-check the voltage and output ratings of your AC and ensure they match the capacitor.
2. HVACPartsUSA – 80/7.5 Dual Run Capacitor – Oval
The 80/7.5 capacitor sold by HVACPartsUSA is an oval capacitor that will fit most Lennox units. If you want or need an oval capacitor, this one will work in most systems. As always, be sure to double-check the voltage and capacitance ratings prior to purchase.
3. Universal 10/5 Dual Run Capacitor – Round
If you aren’t concerned with a name brand match, this universal capacitor will fit a wide variety of models. The 10/5 MFD will replace most 12 SEER and older models.
4. ClimaTek 45/5 Dual Run Capacitor – Round
The Climatek capacitor is made for Trane parts replacement. However, with a 45/5 MFD and 440volt capacitance, it will also fit most modern AC systems up to 14 SEER.
1. Electrolytic Start Capacitor 108/130 Start Capacitor – Round
A lot of start capacitors can be replaced with this 108-130 MFD range round capacitor. Double-check your ratings and ensure you need a capacitor with a voltage output of 125.
2. Trane CPT00091 Start Capacitor – Round
Trane motors need a specific amount of voltage. This 330v capacitor fits the bill for a lot of Trane models. It also has an MFD rating of 135 to 162. A list of compatible Trane units is listed in the description.
DIY vs Professional HVAC Technician
It is never a bad idea to call a professional if you are ever in doubt or uncomfortable working on your own air conditioner. There are a lot of dangers that must be prepared for and expected when dealing with moving electrical parts and high-voltage.
With that being said, you can save yourself hundreds of dollars by replacing the capacitor yourself. You only need a few tools and about 15 minutes of your time to get your AC system back in proper working order.
If you are interested in a DIY project, see below for more details on how to replace a capacitor. For those that cannot be bothered or are too wary of attempting the job, you should look for a professional to get the job done. Angie’s List is a great place to find a licensed professional with a good reputation and acceptable labor charges.
When hiring a professional, make sure you get at least three quotes and know exactly what process they will take when caring for your HVAC system.
How to Replace AC Capacitors
If you have decided to take on the capacitor replacement yourself, there are a few tools you will need:
- A multi-tipped, electrician’s screwdriver. As long as the grip is rubberized to prevent shocks, you will be fine. It should include a Phillips and flathead. If you do not have a ¼ inch driver bit for the screwdriver, a small socket set will suffice as well.
- Needle nose pliers, also with rubberized handles.
- Eye protection. Safety glasses or goggles are a must.
The procedure is a simple one, as well. Remember, though; you are dealing with over 220 volts of electricity. Double-check all breakers and switches are off before opening the access panel.
- Shut the Ac off at the thermostat, then switch the breaker for the AC. Note: Some breaker boxes have up to four breakers for the AC, often the condensing unit is on its own breaker.
- Outside, pull the power disconnect block from the breaker panel.
- Open the access panel. Usually, there are two to four screws that hold the panel in place. Remove the screws and lift up from the bottom then pull out and down to remove.
- Locate the capacitor. Using a rubber-handle screwdriver short the terminals. Place the tip of the screwdriver on a bare terminal and touch a bare terminal of another post with the shaft of the screwdriver. Repeat for all combinations and terminals.
- Remove the screw from the metal mounting strip to release the capacitor.
- Gently pull the capacitor away from the mounting location. Take a photo of the terminals, noting which color wire is connected to the terminal posts. The posts are marked Fan (or just F), Common (or simply C), and Herm (H).
- Using pliers remove the wire terminals from the capacitor port.
- Dispose of the old capacitor properly.
- Push the wire terminals on to the new capacitor ports using the photo from earlier as a guide.
In case you lost the photo or forgot, the general rule is color-coded wires. BE WARNED, not every installation uses the proper color code. This is why it is important to take a photo or draw a diagram before removing the wires. Use the below information only as a guide and not a rule. Every system can be different.
Purple and or red will connect to the common-C post. Bown will link to the fan-F post. Yellow wires will connect to the Herm-H post. Green wires will be a ground wire and not connected to the capacitor. White wires typically don’t appear in AC systems at the condenser; if they do, it is usually a ground wire, especially if a green ground wire is absent. Orange wires will connect to the common-C post.
Also note a start capacitor will be labeled R for Run, S for Start, and C for Common. Red wires will connect to run. Blue wires connect from the contactor to the R or S posts. Brown with white striped wires connect to the Common-C post.
Once the wires are back in place, continue with the installation.
- Position the capacitor against the mounting area of the access panel.
- Wrap the metal strap around and secure it to the wall with the mounting screw.
- Ensure there are no loose wires, or wires laying across contacts or terminals.
- Restore power to the AC unit and turn on to test.
- If everything works correctly, attach the access panel cover back in place. For comfort and safety, you should remove the power disconnect block. However, there isn’t a need to also shut off the breakers inside if you are only attaching the panel cover.
If you want to see a video of how easy it can be to replace the capacitor, you can watch this short video:
Frequently Asked Questions
Here I will answer some of the most commonly asked questions about AC capacitors.
Where can I buy replacement AC capacitors?
AC capacitors are found virtually anywhere AC parts are sold. Many local hardware and home improvement stores will have them in stock or available online. Places such as Home Depot, Lowes, and Ace Hardware are ideal resources. You can always find a specific capacitor through Amazon, as well.
Can start capacitors be interchanged with run capacitors?
Technically, you can, as each does, primarily the same job. However, it isn’t advised and can short out your system. A run capacitor is a long term item that runs as long as there is power to the HVAC system. A start capacitor works much like the starter on your car, only engaging when it is needed. Swapping them or using one instead of the other can cause your HVAC system to malfunction or short out, causing further parts to be replaced.
How long do AC capacitors last?
The average expected life span of a capacitor is about 20 years. This will depend on the overall age of the system, ambient temperature, and amount of usage.
How long does it take to discharge an AC capacitor?
If you discharge with an insulated screwdriver, as mentioned in the article, the discharge takes only a second or two. You can also discharge by using a voltmeter, but depending on the size and capacity of the capacitor, this can take some time.
Do home warranties cover AC capacitor replacement and repairs?
This will be up to your specific contract with your home warranty. HVAC systems are tricky when it comes to home warranties, and many cover some parts, but not all. Other companies will cover every bolt and screw in your home. You will need to contact your home warranty company to find out for sure if you are covered when it comes to the AC capacitor or not.
How much does an AC capacitor typically cost?
The actual cost will vary based on brand, size, shape, capacitance, and other factors. You will also receive a mark-up if you hire a professional, and they supply the part. However, in most cases, a dual-run capacitor form your local hardware store should run you between $5 and $30.
A capacitor going bad or burning out can cause your entire HVAC system to be unresponsive. However, a capacitor is an inexpensive part and quickly replaced by most homeowners. Of course, if you don’t want to be bothered with the project or are uncomfortable working around high-voltage, you can always hire an HVAC specialist to replace it for you.
The overall cost is low, and you won’t be without your cold air for very long. A capacitor will range between $5 and $400, which varies for a DIY project and a hired project. The entire process should take less than 30 minutes before cold air is restored.
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