Skip to main content

How to Diagnose and Repair An Air Conditioner Capacitor

  • Author:
  • Updated date:

Dan has been in the HVAC industry for 23 years with experience ranging from installation and service to sales and distribution.

A capacitor usually resembles a tin can or 9-volt battery.

A capacitor usually resembles a tin can or 9-volt battery.

Air Conditioner Capacitors Commonly Cause Breakdowns

So it's a hot day in the summer sun. The family is coming over this weekend and you're very busy making all the necessary arrangements when suddenly the A/C quits working. Perfect timing, right?

Well, before you call the local HVAC technician to fix the unit and re-allocate the money you were going to spend on burgers, take a quick look. Perhaps you're about to luck out by making a simple repair that will only cost you a few dollars and take very little time. It's also helpful to find out whether your air conditioner is still under warranty, in case you want to replace it later on.

If you need to fix it right away, you won't need any special tools, and you may not have to rearrange your entire day. Just a few minutes, a couple of tools you likely have around the house, and these instructions could save you a significant amount of money while keeping your family gathering right on track.

Quick Overview: How to Replace an A/C Capacitor Yourself

See below for more detailed information and pictures.

StepDetail

1. Turn off the power to the unit at the disconnect or breaker panel.

Do not proceed if you do not know how to do this.

2. Find and inspect the capacitor.

Remove the service panel, locate the start capacitor, and check to see if it's misshapen.

3. Discharge the power of the capacitor.

Be very careful in this step — watch the video below for details.

4. Dismount the old capacitor.

It should be simple to unscrew the metal band holding it in.

5. Note down how the wires connect.

Do this before you remove them!

6. Disconnect the wires.

You can remove them with needle-nosed pliers.

7. Choose a replacement.

Know the micro-farads (μF) and the voltage rating, or the make and model of A/C

8. Buy a replacement and attach.

Check your local contractor supply store.

What Is a Capacitor?

Capacitors are small cylindrical objects that store energy. They either send a jolt to start a motor or send jolts to keep a motor running. They work with the compressor, the blower motor, and the outside fan in your air conditioner.

Checking Your Air Conditioning Capacitor

A voltmeter, if you have one, can tell you if you have blown a capacitor, but it’s even simpler to find out just by watching and listening. Take a walk outside to your condensing unit, and look and listen for the following:

  1. Do you hear any humming?
  2. Do you see the fan spinning?

If the A/C is humming but the fan is not running, you may have a capacitor problem.

A Simple Trick to Test if the Capacitor Is Working

If the A/C is humming but the fan is not turning, find yourself a long skinny stick. Gently slide the stick through the fan grate and give one of the fan blades a gentle push, to see if the fan will spin. If the fan takes off on its own and keeps going, you very likely have a bad start capacitor.

You see, the capacitor is there to give a boost to the fan motor upon startup. A capacitor stores power in a roll of electrically charged sheets of material.

When the capacitor is called to action, it is supposed to release its energy and give the fan a sort of electrical kick in the pants. If the capacitor is shot, the fan can't quite get going from just the 120 volts the motor supplies to it. You and your stick just took over the job of the start capacitor.

There are a few things that could have caused your capacitor to blow. The heat of summer plus motor heat could have proven to be too much for the part, or it could be something else.

Below I'll go over how to fix this problem yourself.

Step 1: Start by Turning Off the Power

First of all, make sure you know how to turn off power to your air conditioner. Don’t proceed if you do not.

Scroll to Continue

Read More From Dengarden

  • Turn off the power to the unit at the disconnect or breaker panel, which should be mounted outside the house within a few feet of the outdoor condensing unit.

It's always a good idea to double-check that the power to the unit has been disconnected successfully with a circuit alert device. There's an example of a reliable and very inexpensive circuit alert device in section three of this article.

The disconnect box for the air conditioner.  The cover opens easily.

The disconnect box for the air conditioner. The cover opens easily.

On this particular disconnect, pulling the handle cuts the power and exposes the fuses.

On this particular disconnect, pulling the handle cuts the power and exposes the fuses.

Step 2: Finding and Inspecting the Capacitor

After you have turned off the power at the disconnect:

  1. Remove the service panel on the A/C unit itself.
  2. Locate the start capacitor. (It's most likely silver, round, or oval, and with multiple prongs on the top for wire connections.)
  3. Look at the capacitor surface where the prongs are attached, and ask yourself: does this surface look raised or domed?

One tell-tale sign that a capacitor is shot is its shape. When a capacitor blows, at least 95% of the time, its top will be pushed up or swollen, somewhat resembling a pop can that has been dropped and is ready to explode when given the chance. Is this what you see? If so, this is good news, and we'll have you back up and running in no time.

It may not be pretty, but there's my capacitor.

It may not be pretty, but there's my capacitor.

Step 3: Discharging the Power in the Capacitor

You've already shut off power to the air conditioner, but now you will have to discharge the power in the capacitor.

WARNING: As I mentioned, a capacitor stores power. That has not changed because you've shut off the flow of electric current. The capacitor may still have power ready to fire. Touching two of the terminals simultaneously with your hand will discharge this power and make for a shocking experience. Throwing away a capacitor that hasn't been discharged could cause a fire in your trash can. Before you continue, discharge your capacitor by placing an insulated-handle screwdriver across the terminals, as shown in the video below.

Video: Discharging a Capacitor

Step 4: Dismounting the Old Capacitor

Now that your old capacitor has been discharged, and you've re-confirmed that no electrical current is in the area where you'll be working with your circuit alert device (above), you can remove it. This is very simple. The capacitor is likely mounted to the unit by a metal band with only one screw to remove. Remove that screw, and the capacitor should come loose from the unit itself.

One screw and it's out.

One screw and it's out.

Step 5: Note How the Wires Connect

Before you remove the wires from the old capacitor, be sure to make a diagram or label showing what wire goes where.

Different colored wires go to different terminals.  This capacitor is good, so the top is flat, but if it were broken the area around the terminals would likely be raised like a shaken pop can.

Different colored wires go to different terminals. This capacitor is good, so the top is flat, but if it were broken the area around the terminals would likely be raised like a shaken pop can.

You can draw a picture showing where the different colored wires will connect to your replacement capacitor.

You can draw a picture showing where the different colored wires will connect to your replacement capacitor.