How to Replace Air Conditioning Fuses
Is Your Air Conditioner Not Getting Power?
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.
- 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.
- 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.
- 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.
How to Test the Voltage on an Air Conditioner
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
Do you know how to test for voltage using a voltmeter?
How to Remove the Fuses
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.