How To Check A Start Capacitor: 11 Steps (with Pictures) - WikiHow

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Terms of Use wikiHow is where trusted research and expert knowledge come together. Learn why people trust wikiHow How to Check a Start Capacitor PDF download Download Article Co-authored by Daniel Stoescu and Hunter Rising

Last Updated: February 19, 2026 Fact Checked

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  • Discharging the Capacitor
    • |
  • Using a Multimeter
    • |
  • Video
    • |
  • Q&A
    • |
  • Tips
    • |
  • Warnings
    • |
  • Things You'll Need
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This article was co-authored by Daniel Stoescu and by wikiHow staff writer, Hunter Rising. Daniel Stoescu is a Master Electrician and the Owner and Operator of Home Tech Solutions, LLC in Hampton, Virginia. With over a decade of experience, Daniel specializes in wiring residential, commercial, and light industrial structures. The Home Tech Solutions team has over four decades of combined experience and offers comprehensive solutions for residential electrical needs. There are 11 references cited in this article, which can be found at the bottom of the page. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 976,727 times.

Start capacitors are used in many home appliances, like washers, refrigerators, or air conditioners. If your appliances are humming but not starting or performing correctly, check the capacitor to see if it’s working properly. By conducting a simple test with a multimeter, you can easily tell if your capacitor is still working or if it needs to be replaced.

Steps

Part 1 Part 1 of 2:

Discharging the Capacitor

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  1. Step 1 Locate the capacitor inside your appliance. 1 Locate the capacitor inside your appliance. Capacitors are metal tubes that store an electric charge usually found near a motor in the appliance. Use a screwdriver to open your machine and locate the capacitor. Use needle-nose pliers with an insulated handle to remove wires.[1]
    • Make sure your device is unplugged and turned off before you find the capacitor.
  2. Step 2 Use a screwdriver with an insulated handle. 2 Use a screwdriver with an insulated handle. Find or purchase the screwdriver from a hardware store. The rubber will prevent electricity from traveling through the metal to your hand.[2]
    • Use caution when working with electricity. A strong enough shock can cause serious harm or death.
    • Make sure the screwdriver’s handle doesn’t have any cracks and that no bit of metal is sticking out the back. This could carry voltage and cause you serious harm.
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  3. Step 3 Wear a pair of gloves meant for housework or working with electricity. 3 Wear a pair of gloves meant for housework or working with electricity. Since you’re using an insulated screwdriver, work gloves will work fine. For added protection against electricity, use tight-gripping gloves made with rubber.[3]
    • Gloves can be purchased at your local hardware or home improvement store.
    • Don’t use large rubber gloves because they will give you less dexterity while you’re working.
  4. Step 4 Hold the handle of the screwdriver so no part of your hand touches the metal. 4 Hold the handle of the screwdriver so no part of your hand touches the metal. Have a firm grip on the handle, making sure you aren’t in contact with the metal. Even with gloves, the current running through the shaft can cause you harm.[4]
  5. Watermark wikiHow to Check a Start Capacitor 5 Place the shaft of the screwdriver on the positive terminal. Set the screwdriver down so the terminal contacts the shaft 1 inch (2.5 cm) from the tip. The correct terminal will be marked with a plus sign (+). Make sure the screwdriver doesn’t touch the other terminal on the capacitor yet. [5]
    • On a capacitor with more than 2 terminals, the positive terminal may be labeled “common” instead.
  6. Watermark wikiHow to Check a Start Capacitor 6 Tap the negative terminal with the tip of the screwdriver. While maintaining contact with the positive terminal, tilt the screwdriver so you make contact with the negative terminal. Once you make the connection, you’ll hear a small pop and see a spark on the tip of the screwdriver. Don’t be alarmed; this is the capacitor discharging completely.[6]
    • Do not hold onto the metal part of the screwdriver while making the connection. Capacitors can store a lot of energy and the resulting spark or current can result in serious injury.
  7. Watermark wikiHow to Check a Start Capacitor 7 Connect the terminals again to remove any residual charge. After the initial spark, keep the screwdriver on the terminals and tap the negative side with the tip 1 or 2 more times. Sometimes, leftover charge is still left in the capacitor.[7]
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Part 2 Part 2 of 2:

Using a Multimeter

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  1. Watermark wikiHow to Check a Start Capacitor 1 Use the capacitance setting on a digital multimeter. Multimeters are electronic devices that read the voltage and capacitance of circuits or batteries. Find a multimeter with a dedicated capacitance setting for the most accurate readings.[8]
    • Make sure the capacitor you’re testing is completely discharged or the circuit is off before using a multimeter.[9] Too high of a voltage can damage the meter or cause you harm.
    • Digital multimeters can be purchased hardware or home improvement stores.
    • Capacitance is measured in farads (F).
  2. Watermark wikiHow to Check a Start Capacitor 2 Place the red probe on the positive terminal and the black probe on the negative. Hold the probes by their base without touching the metal pins on the end. Once both probes come into contact with the terminals on your capacitor, the readout on your multimeter will start to change. [10]
    • Wear gloves while testing with a multimeter if you’re worried about any residual charge.
  3. Watermark wikiHow to Check a Start Capacitor 3 Hold the probes in place until the numbers stop changing. The numbers will fluctuate for a few seconds after you connect the terminals if the capacitor is good. Wait until the readout has the same number for 5 seconds before disconnecting the probes.[11]
    • Write down the capacitance number after you take a measurement so you can remember it.
    • If the numbers do not move at all, the capacitor is considered open and needs to be replaced.
  4. Step 4 Ensure the reading matches the range of numbers on the capacitor. 4 Ensure the reading matches the range of numbers on the capacitor. The minimum and maximum capacitance are listed on the side of the capacitor with all of its other information. The acceptable range depends on the size of the capacitor you have. If the capacitor is above or below the range, it will have to be replaced.[12]
    • If the capacitance number went up infinitely to the limit of your multimeter, the capacitor has shorted out and should be replaced.
    • Some capacitors will have a set capacitance with an acceptable percentage of variance. For example, if your capacitor says “50 ±5%,” the acceptable capacitance range is 47.5 to 52.5 F.
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Community Q&A

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  • Question How do I tell if my capacitor is faulty? wikiHow Staff Editor wikiHow Staff Editor Staff Answer This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness. wikiHow Staff Editor wikiHow Staff Editor Staff Answer The capacitor may have a bulge on top if it's faulty. Otherwise, when you're checking the capacitor with a multimeter, the readings will be far above or below the listed range on the unit. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 6 Helpful 15
  • Question How do i check a start capacitor if my A/C is starting on the heat setting and shutting off after a few minutes? wikiHow Staff Editor wikiHow Staff Editor Staff Answer This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness. wikiHow Staff Editor wikiHow Staff Editor Staff Answer Remove the start capacitor from the AC unit and look for a bulge on the top of the capacitor. Otherwise, use a multimeter to check. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 6 Helpful 12
  • Question How can I tell the high and low parts of a capacitor? Community Answer Community Answer You can use a DMM for this purpose. Connect the probes to the terminals of the charged capacitor. If the reading shows a minus sign then you've connected the positive probe to the negative terminal of the capacitor. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 18 Helpful 26
See more answers Ask a Question 200 characters left Include your email address to get a message when this question is answered. Submit Advertisement

Video

Tips

  • Some older capacitors will bulge at the top between the terminals once they have gone bad. Visually inspect your start capacitor for a small protuberance.[13] Thanks Helpful 0 Not Helpful 0
  • When using a multimeter to test a capacitor, always consult the capacitor’s manual as each make and model could work differently.[14] Thanks Helpful 0 Not Helpful 0
Submit a Tip All tip submissions are carefully reviewed before being published Name Please provide your name and last initial Submit Thanks for submitting a tip for review! Advertisement

Warnings

  • Make sure the screwdriver you use doesn’t have cracks in the handle or exposed metal coming out of the back side. Thanks Helpful 6 Not Helpful 0
  • Never touch the terminals of a capacitor with your bare hands in case it has a charge. Treat every capacitor as if it had voltage.[15] Thanks Helpful 0 Not Helpful 0
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Things You’ll Need

Discharging the Capacitor

  • Screwdriver with insulated handle
  • Needle-nose pliers
  • Work gloves

Using a Multimeter

  • Digital multimeter

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References

  1. ↑ https://www.aces.edu/blog/topics/farming/nptc-tools-of-the-trade-testing-a-motor-capacitor/
  2. ↑ https://www.aces.edu/blog/topics/farming/nptc-tools-of-the-trade-testing-a-motor-capacitor/
  3. ↑ https://www.aces.edu/blog/topics/farming/nptc-tools-of-the-trade-testing-a-motor-capacitor/
  4. ↑ https://www.aces.edu/blog/topics/farming/nptc-tools-of-the-trade-testing-a-motor-capacitor/
  5. ↑ https://youtu.be/ZTQi5rTJIw8?t=3m51s
  6. ↑ https://youtu.be/ZTQi5rTJIw8?t=4m10s
  7. ↑ https://youtu.be/ZTQi5rTJIw8?t=4m55s
  8. ↑ https://youtu.be/hdN0AHzEMAU?t=7s
  9. ↑ Daniel Stoescu. Master Electrician. Expert Interview
More References (6)
  1. ↑ https://www.applianceaid.com/capacitor-testing.php
  2. ↑ https://youtu.be/AYHuJuMPy_A?t=2m38s
  3. ↑ https://youtu.be/AYHuJuMPy_A?t=12s
  4. ↑ https://youtu.be/hdN0AHzEMAU?t=2m29s
  5. ↑ Daniel Stoescu. Master Electrician. Expert Interview
  6. ↑ https://youtu.be/ZTQi5rTJIw8?t=1m30s

About This Article

Daniel Stoescu Co-authored by: Daniel Stoescu Master Electrician This article was co-authored by Daniel Stoescu and by wikiHow staff writer, Hunter Rising. Daniel Stoescu is a Master Electrician and the Owner and Operator of Home Tech Solutions, LLC in Hampton, Virginia. With over a decade of experience, Daniel specializes in wiring residential, commercial, and light industrial structures. The Home Tech Solutions team has over four decades of combined experience and offers comprehensive solutions for residential electrical needs. This article has been viewed 976,727 times. 12 votes - 65% Co-authors: 29 Updated: February 19, 2026 Views: 976,727 Categories: Home Appliances Article SummaryX

To check a start capacitor, start by turning off and unplugging your appliance. Then, use a screwdriver to open the appliance so you can locate the capacitor, which is a metal tube that should be near the motor. Wear work gloves and use a screwdriver with an insulated handle so you don't shock yourself. Once you've found the capacitor, place the shaft of the screwdriver on the positive terminal and tap the negative terminal with the tip to discharge the capacitor. To learn how to use a multimeter to check the capacitor, scroll down! Did this summary help you?YesNo

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Yes No Advertisement Cookies make wikiHow better. By continuing to use our site, you agree to our cookie policy. Daniel Stoescu Co-authored by: Daniel Stoescu Master Electrician 12 votes - 65% Click a star to vote Co-authors: 29 Updated: February 19, 2026 Views: 976,727 Bill Wiltshire Jr.

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"I had an air conditioner repaired and wanted to verify the technician's findings. Your information allowed me..." more Michael Javines

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