How to Replace Air Conditioning Fuses

Is Your Air Conditioner Not Getting Power?

Condenser and Disconnect
Condenser and Disconnect | Source

Why Do Air Conditioners Break on Hot Days?

"The A/C quit working and it's a hundred degrees outside. It's almost like the air conditioner knows how much we need it and breaks down on the hottest days of the year."

This is a statement I've heard so many times in my 15-year HVAC career and it's funny because it's nearly true. Though the air conditioner doesn't have the ability to "know" anything, you're right, it is more likely to break down on the hottest days of the year. This holds true for nearly any electrical appliance.

One of the worst things for electrical equipment, like an A/C, is heat. Increased temperatures cause electrical components to run hotter than recommended and thus fail. When it comes to air conditioning, the capacitor and the fuses that are most likely to "feel the heat". There is very little air circulation to cool these components, increasing their chance of failure. I'm not saying that they will blow, just that the odds are better that they will on a hot day.

Here, we will focus on the fuses and how simple it is to fix this problem. Let's get that A/C up and running again without breaking the bank.

What Do Fuses Do?

Think of a fuse like a secret service agent. It takes the shot. It is designed to handle a limited amount of amperage. Should more amps than the air conditioner can handle try to reach the unit, the fuse will blow to protect the condenser. The same is true of your breakers. Kind of cool, eh?

How to Check if Your A/C Fuses are Blown

If you suspect your fuses may be blown, the first thing you'll notice is that the A/C unit outside is not doing anything. You may hear a slight humming, but that's all. The best way to check the fuse is by using a voltmeter. Let's go through this process first and then, for those of you who don't have a voltmeter, or are uncomfortable testing voltage, I will give you another method for checking the fuses.

REMEMBER! You are working with live electricity here. We cannot test fuses and voltage with the power off or the fuses removed. You should not attempt to work with live electricity if you are not a skilled electrician. In this case, we are taking a simple voltage reading but must still be careful and confident in what we are doing.

  1. Locate your disconnect. This is the usually the grey box mounted to your home near the outdoor condenser part of your A/C system. See the images below for what it looks like.
  2. Open the disconnect. Simply lift or swing open the cover. There may be a small tab on your door that you'll have to apply a bit of pressure to so that the door will open.
  3. Expose the wiring in the disconnect. There should be another cover inside the disconnect that is protecting the wiring, or you, depending on how you look at it. This again should easily pop out or will be held in by just a single screw.

NOTE: Not all disconnects have fuses in them. Though it is most common that they do, and it's code in many states, some do not. If that is the case, they would not be your problem.

Air Conditioner disconnect photo.
Air Conditioner disconnect photo. | Source
Here you can see the door is open and the wiring cover is being removed to expose the wires.
Here you can see the door is open and the wiring cover is being removed to expose the wires. | Source

How to Test the Voltage on an Air Conditioner

Here the "Line" is being tested. You can see the voltage reading here and notice the lugs on either side...that is the "Load" side of the fuses we'll test next.
Here the "Line" is being tested. You can see the voltage reading here and notice the lugs on either side...that is the "Load" side of the fuses we'll test next. | Source

With the wiring exposed, you should be able to see the incoming wiring and the outgoing wiring. The wires will be labeled the "Line", or incoming power, and "Load", the outgoing power. This wiring is not like that of your light switch or receptacle (which run on 110/120 volts) so listen closely. Both wires are carrying 110 volts, not just one.

First, set your meter to the voltage (V) setting and make sure that the display reads "0" volts (or infinity).

The positive lead (+) and the negative lead (-) need to be placed on the "lugs" of the "Line" side of the circuit or fuses. This means that one lead from your meter (red) goes on one "Line" wire (black) and the other lead from your meter (black) goes on the other "Line" wire (white).

Your meter should now read voltage in the range of 220/240, give or take a few volts. If it does, then you've confirmed that you have power coming into the disconnect to your fuses. If not, then the problem is happening at the breaker panel. You may have tripped a breaker and the fuses are likely not your problem, however, let's say you have power.

Now, run the same test but this time, place the leads from your meter to the "Load" side of the fuses. Again, you hope to see the same results as the first test but in this case, the results tell you if the power is making it through the fuses (like it should) by reading 220 volts, or, if it's just sitting on the "Line" side (reading no voltage) which means your fuses are blown and need to be replaced.

Testing for Voltage

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How to Remove the Fuses

Here you see the handle removed and the fuses out.
Here you see the handle removed and the fuses out. | Source

It's possible that your fuses are in the same location as the wiring, fully exposed. However, many disconnects have the fuses in the disconnect's handle itself. This works the same way except that you will have to pull the "T" handle out to see the fuses on that type of disconnect. Either way, you need to pull out the handle to stop power from trying to run through the fuses while you work. This DOES NOT stop power from coming to the disconnect on the line side. You should go back and shut down the breaker to your air conditioner to insure maximum safety.

Now you can remove the fuses either by popping them out with your hands if they are in the handle itself or by grabbing them with a pair of pliers with insulated handles. Never use bare metal handles when working with electricity.

Air Conditioner Breakers

Most air conditioners are wired into a 20 or 30 amp circuit or breaker in a family residence. This breaker will have a doubled switch.

What Kind of Fuses Does A/C Use?

It is important that you buy the right size fuses for your air conditioning system. In a pinch, you could use a fuse that is rated for a lower amperage than the ones you need but never more. Allowing too many amps to flow to your unit will surely do it in. At worst, smaller fuses will blow more easily and overprotect your air conditioner. This means you'll be having this problem again soon.

Many times, the fuse size is written right on the fuse itself. If it isn't, then you should be able to get the amp rating of the air conditioner off of the rating plate on the unit. Sometimes these are located inside the access panel on the air conditioner but not often. It should be rather easy to find. When completely in doubt, go with a 20 amp fuse and see if it blows as soon as you turn it on. If it does, remember, something other than the heat may have caused the fuse to blow and you may want to contact an electrician or an HVAC technician.

If the old fuses are bigger than the new fuses, you will also need to buy what is called a fuse reducer. These will fit onto each end of your smaller fuses and make up the difference of the physical size of the old fuses, not the amperage size.

Short Video on Replacing A/C Fuses

Get the Air Conditioning Working Again!

So this all sounds like a lot but honestly, it only takes a few minutes to do all of this. I just want to help you, inform you, and keep you safe along the way. Just pop the fuses back in where you found them and turn everything back on before you sweat to death!

For those of you who don't have a voltmeter, it's really not a big deal. You should be able to check the size of your fuses, buy them at your local "big box" store, and put them in to test if they were the problem. Worst case scenario is you'll have an extra set of fuses that you should have anyway and will have only spent a few dollars in the process.

I hope this has resolved your air conditioning problem, but remember, there are a few things that could be wrong and if what you find in your system doesn't match up to what I've explained here, don't guess. Contact a professional.

Stay cool, my friends.

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Comments 19 comments

Cre8tor profile image

Cre8tor 2 months ago from Ohio Author

Tony - Thank you kindly for the feedback and am glad I was able to help!

Tony 2 months ago

Great post! Thanks for the information! My AC broke down in the 90+ degree heat yesterday. I followed your instructions and discovered it was a blown fuse. It probably save me hundreds of dollars and I learned something new. Thanks again!

nrgair 11 months ago

Wonderful article! Going to share this. Thank you

Cre8tor profile image

Cre8tor 13 months ago from Ohio Author

Lisaq - I've other articles to help you troubleshoot your problem. Some contractors install non-fused disconnects. In your case, if there is NOTHING going on at the unit, start by checking your breakers. From there, it could be an issue in the furnace. You should at least hear a humming noise if your stat is asking the unit to come on.

Lisaq 13 months ago

What should you do when your unit does not have fuses? There are no sounds coming out of the unit.

Cre8tor profile image

Cre8tor 15 months ago from Ohio Author

Thank you word55! Thank you very much!

word55 profile image

word55 15 months ago from Chicago

Hey Daniel, Congrats on HOTD! These were expertise tips. Actually a great lesson. An AC person probably would charge a hundred dollars or more, without the owner's knowledge that only the fuses may need replacing after a break down. Voted up!

Cre8tor profile image

Cre8tor 15 months ago from Ohio Author

Thank you Charito!

Charito1962 profile image

Charito1962 15 months ago from Manila, Philippines

Thanks for these tips, Daniel! Wow, you sure are a handyman! Now I know how I can cut costs, as I constantly call the A/C service men.

Cre8tor profile image

Cre8tor 15 months ago from Ohio Author

Thank you Kristin!

Kristen Howe profile image

Kristen Howe 15 months ago from Northeast Ohio

Daniel, congrats on HOTD! Perfect timing too, since it's summer when you need ACs. Very good hub on how to replace the fuse in easy steps. Vote up for useful!

Cre8tor profile image

Cre8tor 17 months ago from Ohio Author

Barbara - It's always safest to shut down the breaker unless you have a "pull out" disconnect in where the handle itself holds the fuses, then it doesn't matter but if not and the fuses are held in the box, you still have power on one side of those fuses. As for the number of breakers, if you have more than one double pole breaker labeled to your hvac system, then you likely have a heat pump and back up heating system/air which case only one goes out to the condenser however you could always shut down both to be safe. It is good to know though which is which for future reference.

Barbara 17 months ago

Is it safe to check the fuses without tripping the ac circuit breaker? Circuits are not labeled clearly enough to read and there is more than one double poled breaker.

Cre8tor profile image

Cre8tor 2 years ago from Ohio Author

dedra - My apologies. At first I thought your comment was on another Hub. If you've checked the breaker, fuses and capacitor, it might be time to call a tech. Sorry if that's not what you want to hear. Thank you for reading and commenting.

Cre8tor profile image

Cre8tor 2 years ago from Ohio Author

dedra - That's a very broad question however I'm thinking either the breaker tripped or fuses are blown. I have another Hub on fuses if you'd like to check. That's where I'd start anyway. Always start simple...

dedra 2 years ago

mine is humming and I tried pushing the fan blades but nothing happened.. What else could it be

Cre8tor profile image

Cre8tor 4 years ago from Ohio Author

@furniturez -You're not the only one because we're so used to being charged significantly more for service. Thanks for reading my hubs and I hope they are helpful to you when needed.

furniturez profile image

furniturez 4 years ago from Washington

I had no idea the replacement fuses were so cheap!

Marcy Goodfleisch profile image

Marcy Goodfleisch 4 years ago from Planet Earth

This is one task I could probably do myself - I think! I need to study this and try it whenever my system goes out. It's way cheaper than calling the repairman! Voted up and up, and shared!

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    Daniel Robbins (Cre8tor)318 Followers
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    Dan has been in the HVAC industry for 22 years with experience in aspects ranging from installation and service to sales and distribution.

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