How to Diagnose and Repair Your Air Conditioner (A/C) Capacitor
What's Wrong With Your Air Conditioner?
Capacitors Are a Common Cause of Air Conditioning Breakdowns
Luckily, you can often replace them yourself.
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 come 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 specialty 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.
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:
- Do you hear any humming?
- 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.
Does this sound like what's going on with your A/C?
Quick Overview: How to Replace an A/C Capacitor Yourself
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 mishapen.
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.
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.
- Turn off the power to the unit at the disconnect or breaker panel, which should be mounted on the outside of the house within a few feet of the outdoor condensing unit.
2. Finding and Inspecting the Capacitor
After you have turned off the power at the disconnect:
- Remove the service panel on the A/C unit itself.
- Locate the start capacitor. (It's most likely silver, round or oval, and with multiple prongs on the top for wire connections.)
- 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.
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 at the same time 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
4. Dismounting the Old Capacitor
Now that your old capacitor has been discharged, you can remove it. This is very simple. The capacitor is likely mounted to the unit by a metal band that has only one screw to remove. Remove that screw and the capacitor should come loose from the unit itself.
5. Noting Down 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.
6. Disconnecting the Old Capacitor
Once you're sure where the wires will connect to the new capacitor, you can remove the wires using a simple pair of needle-nosed pliers. If the wires are tight, try not to just yank on them; use a rocking motion while pulling slowly. This will help keep you from touching another terminal, or possibly having the pliers slip and hit you in the face. Don't laugh, I've watched it happen.
That's it. Now all you need to do is obtain the right replacement part and re-install it just as you removed this one.
7. Choosing a Replacement
There are a couple of things you'll want to know when shopping for your new capacitor: the micro-farads (μF) and the voltage rating. The shape and size of the capacitor aren't really important as they can vary and still do the job. Even your mounting bracket will probably bend to accommodate a part of a different shape. Just know that you have to match the micro-farad number exactly. The voltage rating does not have to be identical, as it shows the amount of voltage the capacitor can see, not what it has to see; this means that if you need to you can use a capacitor with a slightly higher voltage rating than what you have now.
Your μF and voltage will be marked on your capacitor and will likely read something similar to 35/5 μF and 370V. If they are not written down, write down the make and model of your air conditioning unit, and use that information at the store or online to find the correct replacement part.
Lastly, brand is not important here. A capacitor is a pretty universal part, and should be available at your local contractor supply company, though maybe not at a Home Depot or Lowe's.
A capacitor for a residential-sized unit should be relatively cheap, and you may consider buying a second one for backup while you are there, along with a couple of spare time-delay fuses (but be sure to buy the right size fuse). In the heat of the summer, blown capacitors and fuses are a very common cause of air conditioner breakdowns. If you suspect fuses are the problem, it is easy to learn how to replace air conditioning fuses.
Get Your A/C Working Again! A Sample 35/5 Microfarad Capacitor
Air Conditioning Maintenance Tips
I hope this was the answer to your A/C problem and that you were able to obtain and replace the part without any hang up for your family get-together.
The heat of the summer sun, added to the heat hard-working motors normally generate, can be tough on our air conditioners, because hot electrical components break down more easily. So it's not surprising a part may fail on a hot day when you need it the most.
Keeping up on your A/C maintenance can help prevent these types of breakdowns. Keeping your air conditioner's coils clean and your air filter cleaned or changed when needed can keep the running temperature of your unit down, thus helping to keep your own temperature down when the summer comes calling.
For those with window units, when winter time comes around, you might want to remove the unit and store it somewhere to protect it from frost, dirt, and debris.
Thanks for stopping by, and again, I hope this helped you and saved you money.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
- Helpful 93
I replaced my capacitor, but the fan still does not spin even if I do it manually. All I hear is a click from the unit when I turn it on. Thoughts?
If that’s all you’re getting it sounds like a power problem. Perhaps a tripped breaker, blown fuse in the disconnect, or maybe a bad contactor. That’s what I’d be looking at. I have written articles on these issues that might help make that determination.Helpful 49
My fan blows inside, and the fan blades spin outside, but the air in the house is hot. Last night, I heard three loud popping noises outside before the AC started acting up. I then woke up to 82 degrees in the house. Could it be the capacitor or a more serious problem?
Yes and yes. It could be a capacitor, or it could be the compressor. Since capacitors are cheap it may be worth a try to see for yourself if that’s it, if not you will need a technician. There is really no “DIY” fix when it comes to repairing or replacing a capacitor.Helpful 4
I just had my A/C unit go out and hired a repairman. He determined that it was the capacitor (45 7.5) and did not have the exact replacement part, so he installed two capacitors one 45 for the compressor and one 7.5 for the fan motor. My question is, is this ok to do (do they work together to ensure the compressor does not go on if the fan fails), and is there a risk that the fan capacitor may go and cause the compressor to break down?
No. What he did here isn’t an issue. I personally would rather have one for the sake of maintenance and space. I would be happy to do this to get a unit running but would probably buy a couple of the original one and put one in and keep the other as a spare due to how cheap they are and commonly the reason for a A/C failure.Helpful 4
My outside A/C runs for about 10 to 15 minutes, and then blows the breaker in the breaker box in the house. Why is this?
Something is either shorted or working too hard (dying) and increasing the amp draw. You should call a tech to run electrical tests and see which component it is.
© 2012 Dan Robbins