How To Order The Right Capacitor For Your AC Unit: A Practical Guide

Kenneth Wilson

Located within the outside component of your AC condensing unit or heat pump, the capacitor plays an important role in the efficiency of your HVAC system. If your capacitor is damaged, it’s really important to replace it correctly so your system works at full capacity. But how do you order the right capacitor for your AC unit?

This article breaks down everything you need to know about choosing the right AC capacitor, so you can get your HVAC system working once again.

Importance of AC Capacitors


The capacitor within an AC unit plays a crucial role in its functionality. Its job is to store the energy until it is required. When needed, the capacitor releases energy to power the condenser or compressor to help you achieve the required temperatures.

The capacitor also provides your AC system with the additional juice that is required to get it started, as most units require more start-up energy than is available through the typical wiring in any household.

Some HVAC units contain multiple capacitors - one in the outdoor unit and one in the indoor fan motor run. Ask any HVAC technician and you will find that capacitor failure is one of the primary causes of faults in AC units, so it’s important to replace your capacitor when required.

How to Choose the Right Capacitor for Your AC


You need to consider three things when choosing the right capacitor for your AC unit:

  • Dual or single-run
  • VAC & MFD rating
  • Dimensions

Let’s take a look at each in detail:

Dual or Single-run


When you come to order a new capacitor for your AC unit, your first job is to work out whether the unit is dual or single-run. As the name suggests, a single-run capacitor connects to one motor and is most prevalent in smaller HVAC systems and portable AC units.

Conversely, a dual-run capacitor includes two capacitors in a single unit. Again, as the name alludes to, a dual-run capacitor is capable of powering two electric motors.

VAC & MFD Rating


Next, you need to take into account the electrical rating of your capacitor. AC capacitors are determined by two electrical ratings: VAC and MFD.

  • Microfarads (MFD) describes the ‘capacitance’ of the unit, which is the charge that the capacitor is able to store after a specific voltage is applied to your system.
  • Voltage Amperage & Frequency (VAC) is simply the indication of the voltage that is needed to power the unit. Crucially, you need to ensure the capacitor that you choose matches the voltage of your AC unit.

If you install a capacitor with a voltage that is too high, you might cause irreparable damage to your AC unit, which could cause the system to fail beyond repair. 

Dimensions


Finally, you should also consider the dimensions of your current capacitor and look for a replacement that is similar in size. While its dimensions aren’t as crucial as its ratings, it’s still worth considering so you don’t end up with a capacitor that doesn’t fit.

If you’re concerned about the dimensions, it’s probably best to take your capacitor to your local Home Depot store to look for a replacement, as it’s not always easy to match the dimensions of your current capacitor with a replacement online.

Now that we’ve looked at the key things you need to consider before ordering a replacement capacitor for your AC unit, let’s look at some of the best options you can find online.

Different Types of AC Capacitors


You probably won’t be surprised to hear that there are lots of AC capacitors to choose from when you head into the online marketplace. So much so, that it can be difficult to know where to begin.

We would recommend you stick to tried and trusted brands wherever possible, even if it costs you a little more. Look for products from TEMCo, MAXRUN, PowerWell, or BOJACK, which are widely available online and in various brick and mortar retailers.

To get your research underway, the following compressors are worth considering:

Brand

Single/Dual

VAC

MFD

Price

Single

370

40

$13

Dual

440

35+5

$15

Dual

370/440

70+7.5

$10 - $15

Dual

370/440

50+5

$17

All of the above AC capacitors are available on Amazon for a very reasonable price. You just need to be mindful of the fact that ordering a capacitor online can potentially cause issues when it comes to dimensions.

Heading to a local store is a good idea if you want to find a capacitor that is of the right size, but you can always return your capacitor if your online order isn’t a good fit.

How Much Does an AC Capacitor Cost?


The good news about AC capacitors is that they’re not expensive. Most are available for less than $20, particularly if you buy them online. While buying a capacitor from a brick-and-mortar store might be a little more expensive, it’s rare to find capacitors that exceed the $40 mark.

Frequently Asked Questions (FAQs)


Will any AC capacitor work on my HVAC system?

No, it’s really important to determine what type of capacitor your HVAC system requires before ordering a replacement. As introduced above, the most important things to consider are whether it’s single or dual-run, the VAC & MFD, as well as the dimensions. If you order a capacitor with a voltage that is too high, you could cause serious damage to your AC unit.

Where is the best place to buy a replacement AC capacitor?

The good news is that AC capacitors are widely available, both online and in brick-and-mortar retail stores. If you prefer to do your shopping in person, head to your local Home Depot store to find the right capacitor for your AC. Alternatively, Amazon is probably the best online retailer to find the replacement capacitor that you need.

Can I replace an AC capacitor myself?

Yes, you can replace an AC capacitor without hiring a professional to do it for you. Make sure you turn the power off and remove the old capacitor from the unit. It’s best to use a multimeter to ensure the unit is completely off before fiddling with the electrics.

How do I tell if my capacitor is bad in the first place?

There are various signs that your capacitor is bad and needs to be replaced, including:

  • The outside fan no longer works
  • Your outside AC condenser unit doesn’t turn on
  • The capacitor is expanding on top
  • The oil from inside the capacitor is leaking

If you investigate but aren’t able to tell what the problem is with your AC system, it’s best to call in an HVAC technician to help you.

Final Thoughts


Helpfully, the process of choosing the correct replacement capacitor for your AC unit isn’t overly taxing. If you follow the steps outlined above and choose a capacitor that is best suited to your system, your AC should be back up and running in no time at all.

Although replacing an AC capacitor is relatively straightforward, if you don’t feel overly confident, it’s best to call in a professional to help you, as you don’t want to cause any extra damage to your unit. (Related: How Long Should Your Home's AC Capacitor Last and Why Does It Cost So Much To Replace?)

Kenneth Wilson
February 8, 2022
Contractor Tips, HVAC

Kenneth Wilson

Retired contractor. Currently residing in Southwest Florida. Now in semi-retirement, I write and manage this blog focused on helping home owners make savvy decisions when it comes to finding contractors and getting their projects done. I also operate remodeling design service for homeowners.

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