Shut off your air conditioner and disconnect it from an electrical outlet. Shut off your air conditioner at the circuit breaker. The disconnect switch is usually near the outside casing. Some models have it on the roof or side of the house. Turn off the thermostat.
Locate the disconnect switch and open the door. Locate the two cartridge fuses with wires connected to terminals above and below it. Using the voltage tester, attach one probe to top terminal and the other probe to the ground terminal on the disconnect switch.
Check the voltage tester's readings. Probe the bottom wires if you do not get a reading. If you are still unable to get a reading, you have a blown fuse.
Pull out the cartridge fuses with your fuse puller. You should see an amperage listed on the fuse. It is usually 30-45amp depending on the model. Check if the unit requires standard, fast or delay-rated fuses. Refer to your air conditioner's documentation if you are unsure. Take the damaged fuse cartridge to retail, hardware or appliance stores to purchase the right replacement fuse.
Install the new fuse using the fuse puller after you purchase it. Make sure to secure it properly into the clamps. Close the door and turn the circuit breaker back on.
Turn the thermostat back on and adjust the settings to your liking.