How to Replace the Fuses on a Central Air Conditioning Unit. During the blistering summer months, there is no place like home--as long as the air conditioning is pumping! Nothing makes your eyes and mouth open in wide surprise as the moment you hear the air conditioning take a dive. The house becomes eerily hushed and the temperature slowly begins to climb. Your home is turning into a sweat box! It may just be that your overworked air conditioning unit blew a fuse. Here is how to replace the fuses on a central air conditioning unit so you can get back to what is really important--relaxing in your lounger with a tall, cool lemonade and chuckling as your neighbor is soaking wet, cutting his grass.
At the beginning of the summer months, it is a good idea to pick up some replacement fuses to have on hand just in case you need them. They are relatively inexpensive and when the temperature is in the 90s, you do not want to wait too long before you get the central air conditioning back up and cooling. The fuses can be purchased at your local hardware store.
Before you pick up your new fuses you have to have an idea of what kind you will need. In most central air conditioning installations there should be a disconnect switch located near the compressor outside. This is where the fuses are located. Before you open up the door on the disconnect switch, turn OFF the circuit breaker delivering power to it. It will usually be a two-pole, 30-amp breaker in your electrical panel, but not always, so be sure to check. In addition, turn OFF your thermostat before you begin troubleshooting your air conditioning unit.
With the circuit breaker and the thermostat OFF, head over to the disconnect switch, turn the switch OFF and open the door. Inside you will see two cartridge fuses with wires connected to terminals above and below them. Take your voltage tester and probe the two wires coming into the disconnect switch which are connected above the fuses (touch one probe to one terminal and the other probe to the other terminal). If you get no reading, probe the bottom wires as well. If you get no voltage readings on any of the wires, then it is safe to proceed.
Use the fuse pullers to pull out the cartridge fuses. There should be an amperage listed on the fuse (typically 30-amp). You will also want to know whether your unit requires standard, fast or delay-rated fuses. For easiest replacing, take one of your fuses to the hardware store and choose one with the exact specifications.
Now that you have your new fuses in tow, test the existing fuses for continuity (see link in Resources below for how to test a fuse). It is possible that only one fuse may be bad, but even if that is the case, I would replace both fuses so you are not in the same position next week.
If the fuses are in fact the problem, then install the replacement fuses. You should use the fuse pullers to insert the new fuses into their clamps. Make sure that the fuses are fully seated into their clamps. Close the door on the disconnect switch and turn the switch back on.
Turn the circuit breaker back on, and lastly, turn the thermostat back on. Dial down your thermostat and you should hear the wonderful click and hum of the central air conditioning kicking on. Ah, the sound of heaven.