How To Wire A Disconnect Box For An Air Conditioner

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Updated June 30, 2022

The best air conditioners allow for built-in safety measures to ensure no one gets shocked during repairs. To that end, we’re going to show you how to wire a disconnect box for an air conditioner. And for more HVAC-related material, we have great articles that discuss leaving an air conditioner on while not at home, how to unlock the A/C thermostat, how to unclog an air conditioner drain pipe, and why the lights dim when the air conditioner comes on.

KEY TAKEAWAYS:

  • Central air conditioner disconnect boxes are a peace-of-mind safety measure that ensures an AC’s power source is completely shut off.
  • It’s crucial to wire a disconnect box correctly and that every wire goes into the proper terminal.
  • There are two sets of wires: one coming from the electrical panel circuit breaker, called the line wires, and the others from the outdoor unit called the load wires.

Wiring An AC Disconnect Box

An air conditioner disconnect box is a safety measure that breaks the flow of electrical current in a given circuit. Before conducting repairs or tests on a central AC unit, owners and maintenance specialists install disconnect boxes to ensure that the power is completely off. For more tips on air conditioner maintenance and projects, you can read our article on how to winterize an air conditioner.

Insider Tip

When sealing your AC disconnect box, seal the top but not the bottom. If any water gets trapped inside, it will drain out instead of stagnating.

STEP 1 Turn Off the Power

  1. Go to the breaker panel and turn off the main power switch and every other individual circuit breaker.

STEP 2 Get Your Wires in Order

  1. There will be two sets of three wires: one set coming from the electrical fuse box called the line wires and another group coming from your condenser fan motor called the load wires. Each of the three wires in both sets will have a different color: green/copper (ground), red, black, and white.

STEP 3 Land the Ground Wires

  1. You’ll see three sets of screws where you’ll attach the wires. There will be two screws next to each other that are lower than the others. These are for the ground wires. Wrap the ground wires around them, and tighten the screws until snug.
  2. There will be four screws above the ground wire screws. The screws on the outside represent the line screws. The inner screws represent the load. There should be labels written under each screw.

STEP 4 Land the Line Wires

  1. Take both line wires (the wires that run to the electrical fuse box) and wrap them around either of the outer screws. It does not matter which one. Tighten the screw until snug.

STEP 5 Land the Load Wires

  1. Now, land the load side wires (the wires coming from the AC unit) by wrapping them on the inner screws labeled “load.” It does not matter which wire goes to which screw.

STEP 6 Turn the Power Back On

  1. Screw the wire cover back on the disconnect box and place the pullout switch back into the
  2. Go to the circuit breaker. Before switching the main power on, switch every other breaker off.
  3. Turn the main power switch on before turning the individual breakers back on.

Warning

Don’t use a metal disconnect box unless you live in an arid area, as metal disconnect boxes are known to rust quickly.

F.A.Q.S

How to clean your air conditioning filter?

Central air units usually have to have filters replaced rather than cleaned. But, if you have a portable or window unit, these come with filters that should be washed or vacuumed every 2-3 months.


How do you check fuses on a disconnected block?

For this test, you’ll need a multimeter. Set the multimeter to the lowest ohms scale and place the ends of the red and black leads onto either end of the fuse. The fuse is good if a number shows up rather than a zero or minus/infinity symbol.


How to clean your air conditioning filter?

You will need to purchase a new disposable filter for central air conditioners. For window and portable units, these will either be washable or vacuumable.


STAT: Installing an AC disconnect box is a project that will cost around $200-$400. (source)

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