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How to Replace Air Conditioning Fuses

Updated on July 10, 2017
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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.

Is Your Air Conditioner Not Getting Power?
Is Your Air Conditioner Not Getting Power? | 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 many times in my 22+ year HVAC career, and it's funny because it's true. Although the air conditioner doesn't have the ability to "know" anything, you're right, your A/C is more likely to break down on the hottest days of the year. This holds true for nearly any electrical appliance.

Heat is one of the worst things for electrical equipment like an A/C. Increased temperatures cause electrical components to run hotter than recommended, and this causes them to fail. When it comes to air conditioning, it is the capacitor and 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 on a hot day.

Here, we will focus on the fuses and how simple it is to fix this problem. Below, you'll find detailed, step-by-step instructions on how to troubleshoot the problem by...

  1. checking the fuses
  2. checking the voltage
  3. removing and replacing the fuses.

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. If more amps than the air conditioner can handle try to reach the unit, the fuse will blow to protect the condenser. It is designed to handle a limited amount of amperage. 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 the door that you'll have to apply a bit of pressure to so that it will open.
  3. Expose the wiring in the disconnect. There should be another cover inside the disconnect that is protecting the wiring (or protecting you, depending on how you look at it). This should easily pop out or it may 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
Air Conditioner Disconnect | Source
Here, you can see the door of the disconnect is open and the cover is being removed to expose the wires.
Here, you can see the door of the disconnect is open and the cover is being removed to expose the wires. | Source

How to Test the Voltage on an Air Conditioner

  1. With the wiring exposed, you should be able to locate the incoming and outgoing wires. The wires will be labeled the "line" (which is the incoming power) and "load" (the outgoing power). This wiring is not like that of your light switch or receptacle (which runs on 110/120 volts), so listen closely: Both wires carry 110 volts, not just one of them.
  2. First, set your meter to the voltage (V) setting and make sure that the display reads "0" volts (or infinity).
  3. The positive (+) and negative (-) leads need to be placed on the lugs of the "line" side of the circuit or fuses. This means that the red lead from your meter goes the lug of the black "line" wire and the black lead from your meter goes on the lug for the white "line" wire.
  4. Your meter should now read voltage in the range of 220 to 240, give or take a few volts. If you see voltage in this range, you've confirmed that you have power coming into the disconnect to your fuses. On the other hand, if there is no reading, then the problem is happening at the breaker panel where a breaker might have been tripped, the fuses are likely not your problem, and it may be time to call an electrician.
  5. If you did see voltage during step #4, then run the same test on the "load" side of the fuses. Again, you hope to see voltage in the range of 220 to 240. This tells you the power is making it through the fuses (like it should). If you read voltage on the line side but not the load side, this means your fuses are blown and need to be replaced.

What Are Leads and Lugs?

The "leads" are the voltmeter's wires. They have hard metal on the end that makes the test safe.

The "lugs" are the screws on the disconnect that are housed in a metal block. They are the screws that hold the wires down. One should say "line" and the other should read "load."

When you test the voltage, you press the metal end of the lead down on the lugs as directed above.

Here the "line" is being tested. The "leads" are what I'm holding here and the "lug" is what I'm touching them to. You can see the voltage reading here.
Here the "line" is being tested. The "leads" are what I'm holding here and the "lug" is what I'm touching them to. You can see the voltage reading here. | Source

Testing for Voltage

Do you know how to test for voltage using a voltmeter?

See results

What If I Don't Have a Voltmeter?

For those of you who don't have a voltmeter, it's really not a big deal. You should be able to find the size of fuses you need, buy them at your local 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.

Here, you see the handle is removed and the fuses have been pulled out.
Here, you see the handle is removed and the fuses have been pulled out. | Source

How to Remove Fuses

  1. It's possible that your fuses are in the same location as the wiring, fully exposed. However, many disconnects have fuses in the handle itself, so you will have to pull the "T" handle out to find the fuses on this type.
  2. Either way, you need to pull out the handle to stop the power from running 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.
  3. Now you can remove the fuses either by popping them out with your hands if they are in the handle itself or, if not, by grabbing them with a pair of pliers with insulated handles. Never use bare metal handles when working with electricity.

So this may all sound like a lot but honestly, it only takes a few minutes to do. Just pop the fuses back in where you found them and turn everything back on before you sweat to death!

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 Fuse 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 cause it to break down. 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. It should be rather easy to find.

If you can't find any amp rating on the fuse or rating plate, go with a 20 amp fuse and see if it blows as soon as you turn it on. If it does, remember that 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 in size than the new fuses (we're talking about physical size here, not amperage), 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.

Short Video on Replacing A/C Fuses

Why Does My Air Conditioner Keep Blowing Fuses?

If your A/C unit keeps tripping the breaker or blowing fuses, don't just keep replacing the fuse. When a fuse blows, that's sometimes your A/C's way of communicating that there's a problem. If the fuse keeps blowing then there's probably a bigger problem with your cooling system and it's time for you to figure out what it is.

There are many possible causes:

  1. It's a problem with your circuit, fuse box, or power supply. Breakers trip and fuses blow when too there's too much voltage in the line. You might try to convince yourself that the solution is to get a larger fuse, but that would be an extremely dangerous mistake.
  2. There's something wrong with the capacitor, which is the part in the condenser that helps regulate electrical current.
  3. Hot weather + a dirty filter (or a dirty condenser coil) = disaster. The unit is struggling so hard to push cool air through a clogged filter that it causes the fuse to blow. You should always thoroughly clean your unit at the start of the warm season.
  4. The filter is clogged or the motor is blocked. When the individual parts aren't working as they should, the whole system has to work harder to compensate.
  5. The electrical connections are loose. Temperature changes can wreak havoc on connections.
  6. It's a faulty condenser fan. If the system can't cool itself effectively, it may blow a fuse.
  7. It's a faulty compressor.
  8. The levels of refrigerant are too high (or too low).
  9. The unit is just too old.

It might be time to hire a skilled HVAC technician or buy a new A/C.

Get the Air Conditioning Working Again!

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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    • Cre8tor profile image

      Dan Robbins 2 weeks ago from Ohio

      Kathy - I've just commented back on your other post and am glad it worked out. I'm sorry I took so long to respond but was on vacation. I'm glad it worked out and thank you again!

    • Cre8tor profile image

      Dan Robbins 2 weeks ago from Ohio

      Kathy - And thank you for the feedback. I like to know I've been able to help people with these minor repairs that can cost them a lot of money. Thank you again!

    • profile image

      KathyJane 4 weeks ago

      I found out that the fuses can go either way, which is what I suspected, but thought I would ask. It turns out that my capacitor was the culprit. The entire top was pushed up and it was very obvious that it was bad. I replaced it, thanks to your instructions on another Hub, and it powered right up. At the time the temperature was 89 in the house and 104 outside! Having a heat wave here in Calif. Cost me $10! Thank you again for taking the time to help others.

    • profile image

      KathyJane 4 weeks ago

      My husband removed the pullout disconnect when our air conditioner stopped working yesterday and both of the fuses fell out. Is there a right or wrong way to put them in? They are 40 amp in a Mars 83317. (The same model you show, only I'm confused as to the direction yours are inserted.) Does the notch go up or down? I bought new and we put them in with the notch down and the condenser unit hums but the fan doesn't turn. Probably the capaciter. We tried to spin the blade and it worked, but no cold air in the house. Thank you for your articles.

    • Cre8tor profile image

      Dan Robbins 7 weeks ago from Ohio

      Beau, Sounds possible that the capacitor is bad. It's a pretty easy fix if so. Cheap too. I've written on the subject here on HP. Thanks for reading and commenting.

    • profile image

      Beau 8 weeks ago

      We have circulation throughout the house, but the AC unit itself won't come on outside and fan doesn't turn. Changed fuses and tried again, but nothing. Any ideas???

    • Cre8tor profile image

      Dan Robbins 8 weeks ago from Ohio

      Power typically enters both fuses from the top and leaves through the bottom. Sounds like you still have one blown fuse. Can't be 100% from here but that's what it sounds like. Thank you for reading.

    • profile image

      Fred 2 months ago

      Hello Dan, My Ac quit so I checked the fuses. Its 240 Volt so I checked both leads from the House Panel and the left side was not getting 120 so I figured it was the fuse. Replaced fuse on the left side and turned on the power at the house panel and checked the voltage at the unit panel and again same issue, the left side no juice. I switched fuses left and right turned on the power again and now the new fuse has power on the right side and the old fuse on the left has no power but it was working on the left side before. I checked the power on the top of the fuse on the left side and it is good but no power at the bottom of the fuse. The T handle is in and I checked power from top to bottom so I know that is good .What am I missing.

    • Cre8tor profile image

      Dan Robbins 2 months ago from Ohio

      There are different kinds but it's often just referred to as the pullout handle, fuse holder, T handle, disconnect...there are a lot of names for it.

    • profile image

      Walter 2 months ago

      What is the part called that holds the fuses

    • Cre8tor profile image

      Dan Robbins 3 months ago from Ohio

      Sounds like it COULD be the contactor. It may be dirty or bad. The hum is the 24v trying to pull in the magnet to complete the connection. If it's humming but nothing is happening...you're hearing it's effort from what I can tell. Be sure to check your breaker first. If you don't have fuses then it may have tripped the breaker. The hum has nothing to do with the breaker power so you can hear that thinking you have power when actually you don't. Just some suggestions and don't mess with the contactor unless you're confident on how to work with the electrical. It's not hard but it can be very dangerous if you aren't sure what you're doing. Thanks for reading.

    • profile image

      Tammy 3 months ago

      Replaced capacitor. Still humming. Inside unit running nothing on the outside. But humming. Any suggestions. We don't have fuses on the outside.

    • Cre8tor profile image

      Dan Robbins 8 months ago from Ohio

      G Attore - Since I don't know what you have, I'm going to suggest you look to a local professional or someone you know who can help. Thank you for reading.

    • profile image

      G.Ettore 8 months ago

      The box containing the fuses is different from the one described by you.

      What should I do?

    • Cre8tor profile image

      Dan Robbins 11 months ago from Ohio

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

    • profile image

      Tony 11 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!

    • profile image

      nrgair 20 months ago

      Wonderful article! Going to share this. Thank you


    • Cre8tor profile image

      Dan Robbins 22 months ago from Ohio

      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.

    • profile image

      Lisaq 22 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

      Dan Robbins 2 years ago from Ohio

      Thank you word55! Thank you very much!

    • word55 profile image

      Word 2 years 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

      Dan Robbins 2 years ago from Ohio

      Thank you Charito!

    • Charito1962 profile image

      Charito Maranan-Montecillo 2 years 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

      Dan Robbins 2 years ago from Ohio

      Thank you Kristin!

    • Kristen Howe profile image

      Kristen Howe 2 years 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

      Dan Robbins 2 years ago from Ohio

      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 handler...in 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.

    • profile image

      Barbara 2 years 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

      Dan Robbins 2 years ago from Ohio

      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

      Dan Robbins 2 years ago from Ohio

      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...

    • profile image

      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

      Dan Robbins 4 years ago from Ohio

      @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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