This Is How To Test A Capacitor For All Heating And Cooling Needs

Heating, ventilation, and air conditioning systems are vital to any home or building space. To maintain comfort and interior air quality, regular maintenance of these fundamental systems is required.  Although diligent maintenance will help prevent any errors, a system malfunction may occur unexpectedly. One of the main elements to examine upon any HVAC system glitch is the capacitor. Below, we have gathered three of our most recommended trouble-shooting methods, which will help guide you in how to test a capacitor.

Notes on Capacitors

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Capacitors are essential voltage storage units placed inline to an electrical component to ensure a constant supply of energy. This is done through the processes of charging and discharging. If the voltage is too high, the capacitor will reduce it. If the voltage is too low, the capacitor will fill the gap with its held charge. Placing a capacitor within an active circuit will either build and store a charge on one of the conductive plates, or it will act to absorb any extra voltage passing through the capacitor. The role of the capacitor depends on the system it is operating in and its classification as electrolytic or non-electrolytic. Within one system, it is common to have multiple capacitors with different functions. Although there are varying functions among these capacitors, it is possible to test capacitors with the same methods. We will now explain how to test a capacitor using three different methods.

Disclaimer  

Please consult with an HVAC professional before performing any repairs if you are not a fluent electrician/engineer. Knowing how to test a capacitor is likely out of range for most people. It is important to remember the dangers of working with electricity. System maintenance can be harmful to you and should be performed with extreme caution and skilled know-how.

How to Test a Capacitor​ in 3 Ways

Method 1: Using a Digital Multimeter with Capacitance Setting

One of the easiest and most accurate methods to test a capacitor is to utilize a digital multimeter that carries a capacitance setting. This is a common function that is found on most mid to high-end readers. The test can be performed by carefully following these steps:

Before You Begin

Before beginning, it is important to disconnect the capacitor from the circuit board and discharge it completely. A great and easy way to discharge the capacitor is to attach alligator cables to both the leads of the capacitor and a resistor. If you have more questions about this step, you should consult a professional as to avoid any potential harm. We are providing this article to help inform people with prior knowledge of electric components in HVAC systems and to suggest our preferred methods of how to test a capacitor to more easily determine whether it requires replacement.

First Steps

Note the capacitor rating which should visible on the body. This capacitor rating is printed alongside the voltage rating on the side of the capacitor. Set the digital multimeter to its capacitance function. Attach the multimeter probes at the proper terminals of the capacitor which you are testing. If you are working with a polarized capacitor, it will be necessary to connect the red probe to the positive slot of the capacitor (this is typically the longer lead of the two). Then, position the black probe with the negative terminal of the capacitor. If this capacitor is non-polarized, then it is inconsequential which way you will attach the probes as there is no polarity.

Take The Test

After assessing the polarity and securing connections between the multimeter and the capacitor, you are ready to observe the readings. You may consider it a “good capacitor” if the values on the multimeter are close to the noted values written on the body of the capacitor. If the values differ significantly or if the reading measures as “0”, the capacitor is “dead”, and it will need to be replaced. We recommend this method of how to test a capacitor because it will give you the most accurate results for the specific capacitor you are testing. It is possible to use this method on various capacitors within the ranges of a few nanofarads to hundreds of microfarads.

Method 2: Using a Digital Multimeter without Capacitance Setting

If you are using a low-end or cheaper digital multimeter, it will probably not include a capacitance setting. We can still test a capacitor using this multimeter; though, the steps will be different. It is important to note the difference between this method and method #1. Though this method may not be the most accurate, it will help you in determining a good capacitor from a bad capacitor. The point of sharing this option is to inform you of the many ways of how to test a capacitor. Also, note that there will be no measurement of capacitance with this method.

Before You Begin

As stated previously, it is necessary to discharge the capacitor entirely before proceeding. Carefully take the capacitor out from the circuit board and perform a discharge with alligator clips cables and a resistor as explained above or consult a professional HVAC specialist.

First Steps

Switch the multimeter to its resistance setting or to “Ohm.” If your device offers several options for measuring resistance, choose the high range (typically considered 20 KΩ to 200 KΩ). Connect the multimeter probes with the correct lead end from the capacitor. Red connects with the positive probe and black with the negative probe if working with a polarized capacitor.

Take the Test

The multimeter should show the resistance measurement of an open circuit. It is important to note this number. To prove the reading, it is necessary to disconnect the meter and capacitor from one another and repeat this same test a few more times. There should be consistent results with this test to show a good capacitor. If there is no change or no measurement reported on the meter, the capacitor is dead. This is the most economical method we offer on how to test a capacitor although it is not helpful in determining capacitance.

Method 3: Testing a Capacitor with an Analog Multi​meter

Using an analog multimeter will allow you to measure different aspects of the electric activity of a capacitor. An analog meter tests AVO, which is current (A), voltage (V) and resistance (O). This test is possible to perform on hole and surface mounting capacitors.

Before You Begin

As previously mentioned, it is imperative to disconnect the capacitor and discharge it entirely. Please view above the method using alligator cables and a resistor or consult with an HVAC professional.

First Steps

After you have discharged the capacitor, place the multimeter on its OHM setting. Choose the higher range if given multiple options. Locate the positive and negative leads of the capacitor to then securely connect them with the analog multimeter probes.

Take the Test

A reading should be immediately observable if the capacitor is good. With this test, the resistance will read low at first but will noticeably increase. If there is only a reading of low resistance without a gradual increase, the capacitor is shorted and will need to be replaced. It is likely that the capacitor is an open capacitor if there is no movement of the needle while the meter is set on its OHM setting. We consider the capacitor as dead in this situation and would require a replacement.
 

Conclusion

Heating, ventilation and air conditioning systems are some of the most crucial aspects of any building or home. Maintaining comfort, air quality, and interior temperature helps create a livable space without the worry of environmental fluctuations, which can easily occur in the outdoors. These systems are part of the reason we find comfort in being indoors and part of why we enjoy shelter. Considering how important these systems are to our everyday life, it is necessary to apply the proper maintenance techniques. Developing a deeper understanding of these systems can also help us find the right professional who we can trust to perform repairs as needed.

Three Basic Methods: How to Test a Capacitor

This article outlines only three basic methods describing how to test a capacitor.  This article is for professional or highly skilled users. Before beginning any kind of service on a capacitor, carefully disconnect the capacitor from the circuit board and ground/discharge it of any remaining electric current. This is a vital step. You may use a digital multimeter with capacitance setting or, conversely, you may use a digital multimeter without a capacitance setting. Finally, we suggest using an analog multimeter which will allow you to test various aspects of the capacitor such as the current, voltage, and resistance.

Any methods described above are for use only by skilled electricians, HVAC specialists, or people who have received extensive training in working with electric components. The information displayed here is not complete, and we highly suggest contacting a professional if you are at all doubtful in executing any aspect of the methods we have shared above. 

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