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Air Conditioner Capacitor

Air Conditioner Capacitor Types


An air conditioner capacitor is a capacitor used for both the compressor (commonly referred to as the hermetic pump) and the fan in an air conditioning system. For smaller systems, these motors are both single phase. For larger systems, they may use a three phase compressor and a single phase fan, or even both a three phase compressor and fan.


These capacitors can either be start capacitors or run capacitors.


Air Conditioner Capacitor - Start

The most common need for replacement of an Air Conditioner Capacitor is the starting capacitor used in single phase compressors or fans. Starting Capacitors create a phase shift during start up of the electric motor to help produce enough torque to bring the motor to full speed.


In hot environments, this capacitor may be over worked and fail prematurely. At this point, a replacement will need to be obtained to bring the system back online. Fortunately, these are very simple to select. Start with the voltage, then capacitance, and finally, you'll need to verify that the capacitor selected will fit within the space available by checking the measurements.

Air Conditioner Capacitor Selection

Air Conditioner Capacitor - Run

The other common type of air conditioning capacitor is the run capacitor. These are used on both single and three phase compressors and fans but are split into two main groups: Single unit (standard) run capacitors and dual-run capacitors.


A single unit run capacitor is used to continuously adjust current or phase shift to a motor's windings in an effort to optimise the motor's torque and efficiency performance. All run capacitors are designed for continuous duty, and as a result, have a much lower failure rate than start capacitors. A single unit air conditioner capacitor will have 2 connections and will be dedicated to optimising current on one motor.


Dual run air conditioning capacitors are 2 run capacitors in one case. They have nothing else that makes them electrically special. They generally have connections marked "C" for "common", "H" or "Herm" for "Hermetic Compressor," and "F" for "Fan." They will also have 2 different capacitor ratings for the 2 different parts. You might see 40/5 MFD, meaning that one side is 40 microfarads (measurement of capacitance), and the other side is 5 microfarads. The smaller value will always be connected to the fan. The larger connection will always be connected to the compressor.


The dual run air conditioning capacitor design's only advantage is that it comes in a small package with only 3 connections. There is no other difference. In a pinch and even as a permanent solution, if there is enough space for mounting, using two separate run capacitors in place of your original dual run motor capacitor is an acceptable practice.


As with selecting a starting capacitor, it's simple. Start with the voltage, then capacitance, and finally, check the measurements of the selected capacitor to verify that it will fit within the space available.

Run Capacitor for Motor Selection

Choosing a Replacement Air Conditioner Capacitor


View our AC Capacitor Troubleshooting page for more information on how to troubleshoot your air conditioner capacitor.



Starting Capacitor Help