A Guide to Finding and Replacing Blown Fuses


As with all electrical devices, air conditioning units can only withstand a certain level of heat before suffering damage. In air conditioners, the most common problem this causes is blown fuses.

Understanding Why Fuses Blow

A fuse protects the electrical appliance on its circuit. If the device attempts to draw an amount of amps which is higher than it can handle safely, the fuse will blow and the amps will not reach the device.

On hot days, air conditioners work extra hard to attempt to compensate for the high temperature. This can lead to them attempting to draw a high amperage and blowing their fuse.

Checking for Blown Fuses

When a fuse blows from the air conditioner, it shuts down. A slight humming may come from the outside equipment, but it will do nothing else. Ensuring the problem is a blown fuse is most easily done with a voltmeter. To check for a blown fuse with a voltmeter:

  1. Find the disconnect. This is usually a grey box mounted on an exterior wall of a home near the outdoor A/C unit.
  2. Open the outer and inner disconnect coverings. This will expose the wiring of the disconnect. Remember that live electricity is running through this and be very cautious.
  3. Zero-out the voltmeter. Ensure the voltmeter is functioning and reading zero volts (or infinity, depending upon the model).
  4. Test the incoming voltage. There will be two sets of wires in the disconnect panel. One should be labeled “line” and the other “load.” The line wires carry incoming power and the load wires send it out. First, connect the voltmeters leads to the lugs connecting the two line wires. The voltmeter should read roughly 220-240 volts. This means power is coming as far as the fuses. If the voltmeter reads nothing on this side, the problem is not with the fuses.
  5. Test the outgoing voltage. After testing the incoming wires, connect the voltmeter’s leads to the load wire’s lugs. If you have a zero volt reading, then you know you have a blown fuse. Otherwise, the problem is elsewhere.

How to Safely Replace Fuses

Fuses may be in the same area as the wiring or may be located in the “T” handle of the disconnect. Either way, pulling the handle is necessary to stop electricity from running through the fuses while replacing them. That only affects the load side, however. To stop electricity coming in the load side, someone must throw the circuit breaker connected to the A/C unit.

Removing the fuses once all the power is off can be done with bare hands or a pair of insulated pliers. New fuses (of the proper amperage) can just as easily be popped back in where the old ones were removed.

Blown fuses can be a hassle in hot summers, but they are easy to detect and fix. The fuses themselves can be removed and replaced with great ease, restoring the unit to working order. If you need assistance diagnosing or repairing a blown fuse, call Woodacre today.

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