Informational Guide

How To Discharge AC Capacitor Safely (Step By Step Guide)

by jtanner

Your residential air conditioner has a lot of electricity flowing through it. That electricity needs to be controlled and reserved, and this is done by using large-capacity capacitors. However, those capacitors will need to be changed from time to time.

When that time comes, you will need to know how to discharge an AC capacitor so that you don’t hurt yourself or cause damage to the HVAC system. In this guide, we will cover all the different methods and help you stay protected while taking on this project.

When researching the discharge process online, you will get a lot of conflicting information. For example, some contractors and technicians will claim they have done it for years without discharging, and nothing ever happens.

It is important to keep in mind, though, that anything connected to electricity (and one that stores electricity) should always be discharged for safety. This section will cover the tools you need to properly and safely discharge your run and motor capacitors. We also cover the precautions, methods, and alternative capacitors to consider.

How To Discharge AC Capacitor

What An AC Capacitor Is For

There are several capacitors in your HVAC system, and they all serve a similar purpose. When the system is turned on, it requires a huge jolt of electricity, higher than that of a normal 240-volt power supply.

A capacitor, also called a run capacitor, stores electricity while the system is running and provides that excess energy jolt when the system starts from a dead stop. These are found for almost all motors in your HVAC system, including the condenser for the fan motor and compressor) and the evaporator unit for the blower motor.

Because these units store electricity, it is important to always discharge them before removal.

Discharging A Capacitor – Tools Needed

Because there are several ways to discharge a capacitor, you will need different tools. Here we have a list of the most common tools needed to get to and remove the capacitor.

  • Eye protection. Small bits of dirt, dust, and metal can fly off when removing. Protect your eyes.
  • Leather or electrical gloves. Every bit of added insulation will help.
  • Multi-use screwdriver. It is important to have an insulated handle and bits to remove the access panel screws on your particular system.
  • Pliers. Both standard snub-nose and needle-nose options are ideal to have on hand, with insulated handles, of course.
  • Capacitor discharge tool. This is a specialty tool designed for discharging your capacitor safely and quickly.
  • Multi-meter. Most multi-meters will have the AC readings and alligator clip tips. Yours should have both of these.

Safety Precautions Before Starting

wiring diagram AC capacitorBefore we get into the actual steps of the discharge process, it is important we discuss safety. HVAC systems use low and high voltage ranging from 10 volts to 240 volts. None of them are pleasant, and you want to protect yourself at all times.

Eye protection and hand protection are a must. Working in tight areas around heavy equipment can lead to many things falling into your eyes. You are also dealing with electrical components and wiring, often by feel. Covering your hands is also recommended.

You also want to know your HVAC system. Refer to the owner’s manual and inspect your circuit breaker before beginning. Some panels will use two breakers for the HVAC system, and others will use three.

You want to ensure power is off to the entire system. Because they are connected, bleed-over is possible. This means that just because the condenser is without power doesn’t mean it won’t get some trickle flow from the powered evaporator unit or the thermostat.

If you are ever unsure of the process, your abilities, or how to test that power is off, please refer to a professional HVAC technician for assistance.

How To Properly Discharge An Air Conditioner Capacitor

The steps to a fully discharged run capacitor are quite short and simple. It is the matter of electrical charge that is the real issue. Let’s follow the steps and get your old capacitor removed from the system. The following steps are known as the AC discharge bleeding method.

  1. Turn off all power to the HVAC system. This includes turning the thermostat off, turning the breakers off at the breaker panel, and pulling the electric cut-off to the condenser unit (usually found outside).
  2. Open the access panel on the condenser unit to locate the capacitor. Most will be on the side of the condenser behind the access panel. Some older models, though, are located inside the unit near the compressor. Use your owner’s manual to find out where yours is.
  3. Identify the wires and which terminals they are connected to. It may be helpful to take a photo before removing the wires and noting the terminals they are attached to before moving forward.
  4. Using the insulated pliers, carefully remove the wires from the capacitor terminals. Pull them out of the way, so they do not touch the terminals or your multi-meter clips.
  5. Clip the negative lead of the discharge tool to the common terminal of the capacitor. Touch the tip of the discharge tool to a ground or even the metal frame of the AC. Wait about 2 to 3 seconds and repeat for the other terminals (Herm and Fan).
  6. Remove the tool from the capacitor and check the voltage with your multi-meter.

Other AC Capacitors Discharge Methods

Other capacitors around your home or in the HVAC system can also be done in much the same way. For example, if you want to know how to discharge your home AC blower capacitors, the steps are identical to those above. The only difference is you are working in the evaporator unit instead of the condenser unit outside.

Microwave capacitors and other types found around the home can also be quite high in voltage, and you should know how to discharge your AC motor capacitor as well as the AC fan capacitors. Once you know how to do one, though, the steps are the same for the others.

The only difference is that the capacitor discharge tool may not be the best option for you. You can then, instead, use a multi-meter to perform the discharge, as covered below.

How To Discharge An AC Capacitor With a Multi-meter

Like using the discharge tool, you can use your multi-meter to discharge a capacitor. This method is slightly safer but can take a much longer time to fully discharge. However, some may not have any other option. Let’s look at the steps required for this process.

  1. Turn off all power to the HVAC system. This includes turning the thermostat off, turning the breakers off at the breaker panel, and pulling the electric cut-off to the condenser unit (usually found outside).
  2. Open the access panel on the condenser unit to locate the capacitor. Most will be on the side of the condenser behind the access panel. Some older models, though, are located inside the unit near the compressor. Use your owner’s manual to find out where yours is.
  3. Identify the wires and which terminals they are connected to. It may be helpful to take a photo before removing the wires and noting the terminals they are attached to before moving forward.
  4. Using the insulated pliers, carefully remove the wires from the capacitor terminals. Pull them out of the way, so they do not touch the terminals or your multi-meter clips.
  5. Set your multi-meter to read in volts AC. Clip the negative cable to the common terminal and the positive to the other terminals in sequence.
  6. As you watch your meter, you are looking for the voltage to drop to zero. This can take some time, depending on the current charge level of the run capacitor.

When To Discharge An AC Capacitor

Safely Discharge AC CapacitorAs covered, an AC capacitor is responsible for storing electrical power and providing a massive jolt to the system to get it to kick on and run when needed. Any time you need to access the electrical components of your AC, the capacitors need to be discharged.

There are a few reasons for this requirement, with personal safety being the top one. However, it also goes into equipment safety as well. If the capacitor gets shorted or grounded, the discharge that occurs can break fuses and damage the capacitor or internal electronics of the system.

Anyone can discharge a capacitor as needed, but you should never feel forced to work with electricity. If you are ever unsure or unable to perform the steps, a professional HVAC technician will be happy to help.

Discharging Capacitor Of Popular Central AC Models

One of the common thoughts about discharging central AC capacitors is that different brands have different processes. However, this isn’t really the case.

For example, knowing how to discharge the capacitor of Rheem central AC units will be identical to how you discharge the capacitor of Frigidaire central AC units. Once you know the proper steps involved, you can perform a capacitor discharge on any standard air conditioner system, regardless of brand or model.

What is important to note (and different) is where the capacitors are located. Each brand is fairly uniform in the parts they use, but the design layout and location may change. This is one of the major reasons for knowing where your owner’s manual is located and how to read its diagrams.

In your specific brand and model manual, it will outline where the various components are located, including the condenser and evaporator run capacitors.

Discharging Capacitor Of Window AC Units

Just like a central AC unit or other primary HVAC equipment set up, window and portable air conditioners also use run and start capacitors. Just like their counterparts, these capacitors also need to be discharged prior to removal.

The actual discharge steps are the same as before, and this will rarely change. However, locating and accessing the capacitor is a bit different. For a window unit, you will need to remove the unit from the window mount and remove the housing covers.

Once the internal parts are exposed, you need to locate the capacitor. Use your owner’s manual for assistance if you can’t see it right away. Some brands put covers over their capacitors to prevent moisture from accumulating on the terminals.

With some brands, you are ready to discharge safely. However, others require that you first remove the capacitor from its mount (with wires attached) so you can properly access the terminal ends and remove the wires without grounding out the capacitor. Otherwise, the discharge steps are the same as outlined above.

Discharging Capacitor Of Other AC Types

Aside from central and window air conditioners, electrical capacitors are found all over. Two of the most commonly accessed are the microwave and automotive capacitors.

For automotive capacitors, the same safety measures are required, but instead of turning off breakers and opening access panels, you only need to disconnect the negative terminal from your car battery.

Once the capacitor in question (AC, radio, etc.) is located, you need to safely remove it and discharge it using a multi-meter as outlined above. Another option, however, is to use a speaker, light bulb, or small motor to draw the electrical charge from the capacitor.

Always make sure the voltage is at or near zero before handling the capacitor after discharge, though. In this YouTube video from ehowauto, the light bulb process is shown in detail.

Frequently Asked Safe Discharging Of AC Capacitor Questions

Is discharging a capacitor with a screwdriver dangerous?

One of the most common methods is to short the terminals of a capacitor with a screwdriver. While this is a fast option and does work, it can break fuses, short circuit boards, and even cause damage to an otherwise healthy capacitor. While it isn’t recommended, it happens every day by many DIYers.

Can you reuse a discharged AC capacitor?

If the capacitor is not bloated, damaged, or burnt, you can reuse a run capacitor in your HVAC system. To ensure the usability of the original capacitor, you must discharge it properly (not using a screwdriver), as we have outlined in the steps above.

Do you need to discharge the AC capacitor before changing the relay?

Yes, the relays and capacitors are all connected to the same electrical source, and power is running through all of them. Before you can remove and replace an AC relay, you need to remove power from the system and discharge the capacitor to prevent damage or injury.

How long does it take a capacitor to discharge on an AC unit?

The time it takes to discharge an air conditioner capacitor will depend on the current held charge, the health of the capacitor, and when the system was last run. On average, with a discharge tool, it can take only a few seconds. With a multi-meter, it may take a few minutes.

Conclusion

Accessing your central air conditioner’s electrical system is a dangerous project. It requires a lot of safety measures, understanding, and proper tools. However, before you can even begin to remove or replace electrical parts, you need to know how to discharge an AC capacitor.

Your HVAC system will have a few capacitors, but the run and start capacitors in the condenser and evaporator units are the most important. Hopefully, now, you have a better understanding of what the capacitors are and do, and how to safely discharge them for service or replacement.

Last Updated on January 9, 2023

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