What Is an AC Capacitor – Most Commonly Replaced AC Part

What is an AC Capacitor? How Long Does a Capacitor Last?

This guide explains what this vital AC and heat pump part is, what it does, what replacement cost and other FAQs. 

What is an AC Capacitor?

An AC capacitor, or any type of capacitor, is a battery-like device that holds an electrical charge. It releases that charge to give a motor, like an AC fan motor or blower motor, a little extra “juice” at the start – extra torque to get the motor going. For example, a start capacitor supports an air conditioner or heat pump compressor when an AC or heat cycle is called for by the thermostat. For this reason, one is commonly called a start/run capacitor.

Capacitor Failure: Because of the constant cycles of charging and discharging electric, the capacitor is one of the first parts of an HVAC system to wear out and require replacement. The good news is that replacing the part is pretty easy – even a DIY option for those with basic skills who enjoy accomplishing repair projects. If you want to learn more about this subject, see the Pick HVAC AC Capacitor Cost and Replacement Ultimate Guide. It’s another in a series of useful, detailed FAQ guides we produce for readers that want to make the repair without calling an HVAC technician or that want to be more knowledgeable when discussing the repair issue with a repair tech.

AC Capacitor Location

AC Capacitor Location

Where is the AC capacitor? AC capacitor locations vary, but they are usually located very close to the specific part of the air conditioning unit they are designed to help power, such as the compressor or blower motor in a furnace or air handler. Those installed in the outdoor unit are placed in a covered location to protect their electrical connections from rain.

How Many Capacitors Are in an AC Unit or Heat Pump?

One or two. But this is a bit of a trick question. If there is only one capacitor, it might be a dual capacitor, aka a dual run capacitor, that serves the fan motor and the compressor. Or there might be separate capacitors for each part, so two capacitors total. In some units, there will be a capacitor to start the AC unit (start capacitor) and another one to keep the air conditioner running properly and as needed (run capacitor). 

Details: Air conditioners might have a start/run capacitor (single run) or dual run capacitors.  The start/run capacitor has the purpose of giving the air conditioning unit a boost or push to get it started and to keep it running, as needed.  Dual capacitors are used for more than one part of the AC or heat pump unit.  They give a boost of energy to parts such as the fan motor and the compressor. 

How Long Do AC Capacitors Last?

The capacitors in your AC unit will usually last 8-15 years, but they have been known to last as long as 20 years. AC capacitors are not a moving part, but they do fail or burn out over time, as are prone with electrical parts.  Usually, an AC capacitor will need to be replaced every 10 to 15 years.  There are a number of different factors that will affect the lifespan of a capacitor.  First of all, if you live in an area with extremely high temperatures, your AC unit will have to work harder and the AC capacitors will need to be replaced earlier than if you live in a more mild climate. 

Capacitors also fail if the wrong size or type of capacitor is used in the AC unit.  Oftentimes a homeowner will replace the AC capacitor, but not use the correct size, so the capacitor will continue to “burn out” and stop working.  A third factor that limits the length of time an AC capacitor will work is simply age.  As an AC capacitor gets older the ability for it to hold energy diminishes. 

How Do I Know if My AC Capacitor Needs to be Replaced?

Once the AC capacitor in your AC unit or heat pump begins to fail or go bad there will be some telltale signs that will indicate you will need to replace the capacitor.  Below are a list of the most common issues that will occur due to a bad capacitor:

The AC unit stops blowing cold air (blower motor capacitor or compressor capacitor)

  • Rising and/or higher than normal energy costs as a result of the system not working properlyA non-normal humming noise coming from the AC unit
  • Your air conditioner shuts off before the thermostat setting is reached
  • The AC fan struggles to turn on – or it won’t start spinning

Pro tip on a fan capacitor: There’s an old trick to determine if your fan motor capacitor is bad. When an AC cycle (AC or heat cycle with a heat pump) begins, use a stick to push a blade of the fan to give it the boost of energy a capacitor normally would. If the fan starts spinning – and keeps spinning – then the capacitor failed to give it the initial boost of electrical power. The capacitor should be replaced.

Can I Run My Air Conditioner or Heat Pump with a Bad Capacitor?

If it’s the fan motor capacitor, then the trick just described will work, and you can run your AC or heat pump with a bad capacitor. But it’s a major hassle having to go outside to get the fan started each time the unit comes on.

Even though your air conditioner or heat pump may be able to still run and function with a capacitor that needs to be replaced, you should not do it for long.  Running an AC unit with a bad capacitor will cause your air conditioner to work harder than normal and also possibly cause more damage to your heating and cooling system.  This could result in a more expensive fix than replacing your AC capacitor.

Can I Replace an AC Capacitor Myself?

If your AC unit stops working or is showing signs of not working properly then there is a good chance that you will need to replace the AC capacitor. 

As we said above, this is something that a homeowner can do, but it is not the easiest “do it yourself” task.  The following are the steps you can take in order to replace the AC capacitor in your home AC unit by yourself:

  1. Turn off the power to the AC unit.  This can be done by using your breaker box and turning off the proper breaker that powers your AC unit.  DO NOT start any work on your AC unit without double checking that the power is off.
  2. Locate and remove the panel where the electrical lines run into the AC unit.
  3. Locate the start/run or dual capacitor that you will be replacing.  They are cyclical in shape and look a lot like a battery.  It is a good idea to take a picture of the capacitor before you disconnect the wires that feed into it.
  4. Discharge the AC capacitor.  Even though the power is turned off there will still be an electrical charge stored in the capacitor.  Touching the terminals on the AC capacitor will shock you!!  You might benefit from a tutorial video on how to safely discharge a capacitor.
  5. Disconnect the capacitor for the AC unit.  Do not touch any of the connections or terminals with your hands.  Always use needle-nose pliers with rubberized, shock-resistant coatings on the handles.
  6. Make sure that the new capacitor has the proper MFD (milliFarad) and voltage.  Using the picture you took of the old capacitor, connect the proper wires to the new capacitor.  Do one connection at a time.
  7. Replace the electrical panel, turn on the power for your AC unit, and power up your air conditioner.

Everything should be working correctly, and your house will be at a comfortable temperature very soon.

Frequently Asked Questions

Here are a few questions we get. Some of the answers have been given above, but the answers will clarify the issues.

How much does an AC capacitor cost?

Buying an AC capacitor will cost anywhere from $5 all the way up to $100.  Most cost $15 to $30, so they’re not a pricey part. But again, make sure you get one with the same specifications as the one you are replacing!

This cost is for the capacitor only. The cost to have a pro install it ranges from about $65 to $150.

What type of capacitor does my air conditioner use?

It varies by brand and model. All air conditioners will have either a single or dual AC capacitor.  You can tell what type of capacitor your AC unit has by looking at the number of terminals that are on the top of the AC capacitor.  Single run capacitors will have two connecting terminals and a dual run capacitor will have three.

How much does it cost to have an AC capacitor replaced?

If you decide to hire a professional HVAC technician to supply the part and install it, your total cost will range from about $80 to $150 or $200 tops. If you get estimates higher than that, ask for an explanation. It could be that the part is a unique one. Some Carrier and Lennox capacitors cost around $100.

How long does an AC capacitor last?

A capacitor for your air conditioner or heat pump can last up to 20 years, but they normally need to be replaced after 10-15 years of usage.  How much you run your air conditioner and where you live will play a factor in how long your AC capacity will last.

What is the difference between a single run capacitor and a dual run capacitor?

Single run capacitors have a single function, such as starting a fan motor, blower motor or compressor. Single capacitors have two connecting terminals.  Dual run capacitors are used to give an energy boost to two parts of the air conditioning system, and they have three connecting terminals.

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