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How To Wire A Mini Split

How To Wire A Mini Split

Jon Hubal
7 minute read

As a do-it-yourselfer, you may be considering installing your mini split system. While mini splits can be an affordable and energy-efficient alternative to central air conditioning, wiring one incorrectly can be dangerous. Before you start the installation process, review the instructions thoroughly and make sure you understand the steps involved and have the necessary tools and components. Read on to learn How To Wire A Mini Split.

How To Wire A Mini Split

How to Connect the Mini Split Disconnect

To properly connect the mini split disconnect, you will need to turn off the power to the unit at the breaker before beginning any wiring. Locate the disconnect box, which will be within sight of the outdoor unit. Open the disconnect box to access the wiring connections and wire a mini split

Inside the disconnect box, you will find three wires: the power supply wire and two wires that run to the mini split outdoor unit. The power supply wire will typically be red and black, while the wires running to the outdoor unit are usually labeled as L1, L2, and L3, indicating the three power phases.

First, connect the red power supply wire to the L1 terminal in the disconnect box. Then, connect the black power supply wire to the L2 terminal. Finally, connect the remaining wire from the outdoor unit to the L3 terminal. These connections provide the necessary 220-240V power to the mini split.

Once the wires have been securely connected in the proper configuration, turn the power back on at the breaker. The disconnect box will now function as an emergency shutoff switch for the mini-split. To shut off power to the unit for any reason, simply flip the switch on the disconnect box to the ‘off’ position. Take appropriate safety precautions any time the disconnect box is open.

How To Wire A Mini Split

How to Wire A Mini Split Unit

To wire a mini split unit, follow these steps:

  1. Turn off the power supply to the area you will be working in at the circuit breaker. Verify power is off with a voltage tester.

  2. Locate the pre-installed low-voltage whip or cable coming from the outdoor unit. This will be the power supply for the indoor unit. Pull the cable through the hole in the wall and extend it to the location of your indoor unit.

  3. Find the terminal block or wiring compartment on your indoor unit. This is where you will make the power connections. Open the wiring compartment to access the terminals.

  4. Match up the colored wires from the low-voltage whip to the terminals on the indoor unit. Typically, the red wire is connected to the "R" or "HOT" terminal, the yellow or white wire is connected to the "Y" or "COM" terminal, and the green or bare copper wire is connected to the "G" or "GROUND" terminal.

  5. Connect the matching colored wires to the proper terminals and secure the wires in place, often using screws on the sides of the terminals to tighten the connections. Ensure no bare wire is exposed and the connections are tight.

  6. Put the wiring compartment cover back on the indoor unit and turn the power back on at the circuit breaker.

  7. Test your mini split to ensure it is powering on and cooling/heating properly. Make any final inspections to guarantee all connections are secure before closing up the wall.

How To Wire A Mini Split

Connecting the Ground Wire

To connect the ground wire:

  1. Locate the green grounding wire in the mini split wiring harness. This wire will be green or bare copper.

  2. Attach the grounding wire to the grounding lug or grounding screw on the outdoor mini-split unit. The grounding lug is typically a green screw with a wing nut.

  3. Run the grounding wire to the grounding rod. The grounding rod is a copper rod driven into the earth near the outdoor unit that disperses electric current into the ground.

  4. Attach the grounding wire to the grounding rod using a grounding clamp. Ensure the connection is tight and secure.

  5. Label the grounding wire at both ends to indicate it is the ground connection. This helps ensure proper wiring if service is needed in the future.

  6. Test the ground connection to verify it is providing a path to the ground. This can be done using a multimeter set to measure ohms. The resistance between the grounding wire and an earth ground should be very low, around 25 ohms or less.

  7. Once the ground connection is verified, you can turn on the power to the mini-split and test the operation. The unit will not function properly without a secure ground connection.

Installing the Power Supply

To install the power supply for a mini-split, follow these steps:

  1. Turn off the power supply to the mini split unit at the breaker box. Ensure all power is disconnected for safety.

  2. Locate the power inlet on the outdoor condenser unit. This is where the power cable will be connected. The inlet will be clearly labeled.

  3. Connect the power cable to the inlet, securing it in place. The power cable will run from the condenser unit to the power supply.

  4. Install a dedicated circuit breaker in your breaker box for the mini split. A double pole 30 amp breaker is typical for a standard residential unit. This will ensure the mini-split has a consistent power source.

  5. Connect the power cable to the circuit breaker, powering the cable.

  6. Connect the grounding wire to the condenser unit and circuit breaker. Proper grounding helps prevent electric shock and ensures safe operation. The grounding lug will be located next to the power inlet.

  7. Power on the circuit breaker to begin supplying power to the mini-split.

  8. Turn on the mini-split to test the power connection. Check that the unit is receiving power and functioning properly.

  9. Power down and inspect all connections once more to ensure they are secure before continuous use.

Testing Your Mini Split Wiring

Once you have wired your mini split unit, it is important to test that all connections are secure and the installation is functioning properly before leaving the job site.

To test your mini split wiring, follow these steps:

Power On the Unit

  • Turn on the power supply to the mini-split system. This will provide power to the indoor and outdoor units, as well as the wiring connecting them.

Check the Indoor Unit

  • At the indoor unit, ensure the unit powers on and the display is functioning. Test that the thermostat is working properly by adjusting the temperature settings. Activate the heating and cooling modes to confirm the unit responds and starts blowing conditioned air.

Inspect the Outdoor Unit

  • Go outside to the outdoor condenser unit. The unit should be receiving power and actively blowing air from the fans. Some clicking or buzzing noises are normal as the compressor and fans start up. However, loud grinding or squealing sounds could indicate an issue.

Test Emergency Features

  • If your mini split has emergency heating features, test to ensure these are functioning properly by activating emergency heat mode. The unit should blow warm air within a few minutes.

Double Check Connections

  • With the power still on, double-check that all wiring connections are securely fastened with no exposed or frayed wires. Tighten any loose wire nuts or terminals. Ensure the conduit protecting the lines between the indoor and outdoor units is also securely installed with no damage.

Monitor Operation

  • Run the mini split for at least 15-20 minutes to ensure continuous, normal operation. Check that no error codes appear on the display and that the desired room temperature is being reached. Shut off the unit and recheck all connections for any signs of overheating before leaving the job site.


Having come this far, you're almost ready to enjoy the comfort and efficiency of a mini-split system. A mini-split can make a big impact on your home's comfort and energy usage. With some patience and the right tools, you've proven that installing one yourself is an achievable DIY project. Turn it on, sit back, and enjoy the perfectly controlled temperature in your space. You've earned it after a job well done.

Explore an abundance of online resources to deepen your knowledge of mini-split systems. Browse through our collection of related blog posts, including our comprehensive guide on the Best Mini Splits of 2023 and their suitability for your needs. Additionally, discover valuable insights on How to Size a Mini Split and embark on a DIY Mini Split System installation journey.

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