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Air Compressor Capacitor Guide: How to Size a Capacitor for a Compressor

Published Categorized as Air Compressor Motor Guides 10 Comments on Air Compressor Capacitor Guide: How to Size a Capacitor for a Compressor

When either one or both air compressor motor capacitors fail, you will need to replace them. But what capacitor does my compressor need? And how do you size the starter capacitor? These are two questions many compressor owners ask on this site.

This is because OEM parts can be expensive and finding a source for the capacitor of a low-cost air compressor can be a challenge.

This page will provide you with all the relevant information about capacitors as well as some replacements readily available on Amazon.

Table of Contents

What Are Air Compressor Motor Capacitors?

Without getting into too many details, the compressor capacitor typically sits on the side of the compressor motor on the outside of an air compressor, near the motor shaft. It may also be under a motor capacitor cover.

Some air compressors have more than one start capacitor. Each compressor will have a start capacitor while some have a start and run. Others have a combination of start/run capacitors. Start capacitors are only used once when switching on the air compressor, while run capacitors help with the ongoing running of the compressor motor.

Where to Find the Capacitor for an Air Compressor Motor

In the image below the red dot identifies the capacitor housing on a typical compressor motor. The capacitor sits inside the housing. Your compressor motor might just have the capacitor itself attached or adjacent to the motor rather than inside a housing as the one in the picture is.

Air Compressor Capacitor Guide: How to Size a Capacitor for a Compressor
What Capacitor Does My Compressor Need Capacitor Housing On Electric Motor

Safety Note: Be careful not to touch the capacitor terminals as a capacitor is a high-discharge device. You may get a severe electric shock from the stored energy. If unsure, please seek professional guidance while fixing the air compressor. It is also advisable to test the capacitor with a voltmeter to check the state of charge.

What Capacitor Does My Compressor Need?

To help you better visualize one, here’s a capacitor from a Campbell Hausfeld air compressor motor. In the quest to find an air compressor capacitor replacement, know that compressor motor capacitors have two ratings:

  • Voltage
  • Capacity
Air Compressor Capacitor Guide: How to Size a Capacitor for a Compressor
capacitor for air compressor


On the side of the capacitor, there should be a label. This label shows the ratings of the capacitors, one of which is the voltage. Typically the voltage range will be 120-240 Volts. In this image the capacitor voltage is 250V AC, meaning 250 volts, and an alternating current type capacitor.

As long as you get a capacitor that has the same voltage range as the one you currently have, then the voltage will be satisfactory for your air compressor motor.


Another rating noted on the label will be the microfarad capacity. It may show as an MFD rating, MFD being the acronym for micro-farad.

Air Compressor Capacitor Guide: How to Size a Capacitor for a Compressor
What Capacitor Does My Compressor Need Air Compressor Motor Capacitor

These are different ways that identify the microfarad rating of that capacitor.

Wondering what starter capacitor my compressor motor needs? You need to get one that has the same microfarad rating as the existing capacitor, or, one that shows a microfarad range into which the existing capacitor range fits.

Note: If your replacement capacitor is too low the air compressor will not start, if it’s too high then you are likely to cause electrical faults.

Replacing the Start Capacitor for Air Compressors

The last thing you need to figure out is whether or not the new capacitor will fit on your compressor motor. Typically they all have terminals to which you connect the wires to the motor, yet what I’m referring to here is whether the new capacitor will fit inside the existing capacitor housing or not.

You see, if the new capacitor has the same voltage range, the same microfarad range, and you can attach it to the existing mounting of the motor capacitor on your compressor, you can use it. Even if it’s a different shape, a different color, longer or shorter, or a bigger circumference, as long as the voltage and microfarad ratings are the same, it is a suitable capacitor for your compressor motor.

If you’re unsure if your capacitors are being problematic then check out our how-to test air compressor capacitors page to learn how to do so correctly!

Air Compressor Capacitors Available on Amazon

The first is an HQRP 100uf 250VAC run capacitor that is compatible with Campbell Hausfeld.

The next is a 120uf 450VAC CBB60 run capacitor which is an Amazon choice.

Another is the 12uf 370-440VAC HQRP run capacitor which boasts terrific reviews and is a best seller!

A final is the Appli parts start capacitor which is suitable for ranges 216-259Mfd and 110-125VAC.

FAQs (Frequently Asked Questions)

What are the symptoms of a bad start capacitor?

Here are the most common symptoms of a bad start capacitor:
1. Air compressor won’t turn on
2. Air compressor doesn’t turn on immediately
3. Air compressor cuts out
4. Air compressor capacity blows
5. Air compressor capacitor casing melts

What capacitor do I need for my air compressor?

You need a capacitor that matches your air compressor’s requirements for its voltage (V) and microfarad capacity (uF). You can typically find this in your air compressors manual, or by buying the exact capacitor specs as the one you’re replacing.

What does a capacitor do on an air compressor?

The capacitor modulates the current and voltage to the air compressor motors run windings and can be considered as a continuous-duty device. If the capacitor fails, your air compressor will not start or run properly.

Reader Questions & Responses

A number of air compressor capacitor reader questions and responses are available on this site:

Compressor motor start capacitor is blowing

Clarke Rebel 60 240v capacitor casing has melted

Piston Head heats up and the motor capacitor blows off

Replace capacitor in 1998 Clarke air compressor

Harbor Freight 90234 run capacitor exploded

The Air compressor capacitor keeps blowing

Capacitor for Central Pneumatic 67847

Husky Pro Air Compressor Motor Won’t Start?

Is Charge Air Pro compressor getting hotter than normal?

If you have any questions regarding air compressor capacitors and how to size them, please leave a comment below with a photo if applicable so that someone can help you!

By Bill Wade

About Air Compressors has been helping folks with their Air Compressor Problems since 2002 online. We're a community of DIY and Compressed Air professionals who are keen to support everyone across the globe with their air compressor issues and troubleshooting. Whether you're trying to identify an old air compressor, or troubleshoot an error code on a sophisticated new industrial air compressor - the community at About-Air-Compressors.com is here to help you

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