DIY Guide: Install Your Own MRCOOL Ductless AC & Heating Mini Split System

How to Install a DIY Mr. Cool Mini-Split System for Your Garage

Hello, fellow DIY enthusiasts! Today, I’ll be diving into a detailed guide on how to install a Mr. Cool mini-split air conditioning system in your garage or any other workspace. If you work in a garage, shed, or any building that lacks adequate temperature control, you know how unbearable it can get. Hot summers can turn your workspace into a sauna, and cold winters can transform it into an icebox.

After much research and contemplation, I settled on the DIY Mr. Cool mini-split system. It fulfills my requirement for an easy-to-install HVAC solution without needing professional intervention (except for a bit of electrical work if you’re not comfortable doing it yourself). So, let’s delve into this step-by-step installation process, which, based on my experience, can make your workspace comfortable all year round.

Choosing the Right Spot for Installation

The first and probably the most crucial step is choosing a suitable location for both the indoor and outdoor units. I chose to place the indoor unit above the door to the garage. However, due to drainage concerns, I couldn’t perfectly center it, which did drive me a bit crazy at first. You need to respect the configuration of your drain line and ensure it runs straight outside.

For the outdoor unit, I aimed to place it under an existing air conditioner pad. Fortunately, the condenser isn’t overly heavy, so if you need to mount it on a wall, it shouldn’t be an issue. Consider the ease of access for maintenance when selecting your outdoor unit spot.

Preparing for Installation

Once the indoor location was set, I proceeded to trace the mounting holes directly on the wall. Unfortunately, I misplaced the mounting template that came with the unit, so I had to go about this the hard way. If you still have your mounting template, it will save you some time.

Drilling Through Concrete

My house is constructed from CBS (Concrete Block Structure), requiring more specialized tools to drill three-and-a-half-inch holes through solid concrete. Start small with a masonry bit to reduce blowout and gradually increase the size of the hole. If you’re drilling from outside to inside, blowouts won’t be a significant concern. Just be cautious when the drill bit exits the concrete.

Cutting Through Drywall and Framing Strips

Cut away the drywall and framing strips to create a passage to the attic. Once your path is clear, push a pull cable through the hole. This cable is essential for guiding the refrigerant lines and electrical harness from the indoor unit up into the attic.

Precautions with the Harness

Within the harness are the two copper refrigerant lines and an electrical wire. Avoid sharp bends and ensure everything runs smoothly. This harness needs to be treated gently to prevent any damage during installation.

Installing the Indoor Unit

With the mounting holes and harness passage prepared, it was time to mount the indoor unit. The unit is relatively light but handling it with the attached harness can be tricky. After mounting, connect the drain line, ensuring it runs directly outside.

Using wall anchors since my bracket didn’t line up with any studs, I lifted the unit and secured it to the wall. Precautions like using strips to lift the harness off the attic insulation will later help in the overall durability and functionality of the system.

Addressing Outdoor Setup

For the outdoor unit, I drilled up through the soffit to create a passage for the harness. Using a separate cover kit from Amazon, I was able to keep things tidy and visually pleasant by hiding the harness. This kit worked excellently, and I highly recommend getting one for a clean finish.

Connecting the Electrical Components

If you’re not confident with electrical work, now might be the time to consult an electrician. However, if you’re up for the challenge, here’s what you need to do:

Liquid Tight Conduit

Run the power cable through a liquid-tight conduit. This flexible tubing protects the wires and makes routing easier. Use fish tape to pull the wires through the conduit.

Connecting to the Sub Panel

For my setup, I used an existing sub-panel in my garage. Your Mr. Cool unit requires a dedicated circuit, either 15 or 20 amps, depending on your specific model. In my case, I temporarily used power meant for a sprinkler system which I no longer use.

Wiring the Unit

Start by connecting the ground wire from the indoor unit. For a cleaner finish, I used crimped spade terminals to connect the necessary wires. Connect the green terminal to the ground, the black wire to the line, and the white wire to the neutral terminal.

Safety and Final Checks

Always remember to leave caps on refrigerant lines until you are ready to connect them to avoid contamination. Tighten refrigerant lines by hand initially to prevent cross-threading. Use wrenches for the final tightening, but avoid using pliers to prevent stripping the threads. The Mr. Cool system comes pre-charged with refrigerant, meaning you only need to open the valves to start the flow.

Starting Up and Testing

Before firing up the unit, ensure all connections are secure and tight. Open the refrigerant lines by turning the valves counterclockwise until they stop and spray soapy water on all connections to check for leaks. No bubbles should indicate a tight seal.

Powering Up

For an initial power source, I used a nearby outlet connected to my sprinkler system. Ultimately, I’ll run a dedicated line from my sub-panel to this unit. Plug in the unit and ensure it is operationally supported by a sufficient power source.

Managing the Excess Harness

One of the minor challenges with the DIY Mr. Cool system is the fixed 25-foot harness. You can’t cut this down, so you must accommodate this length in your setup. Storing the excess harness in the attic was a practical solution for me, but your installation might vary. Consider constructing a small box if the harness needs to remain outside, ensuring it is safe and sheltered.

Utilizing Smart Features

The Mr. Cool mini-split system comes equipped with a Wi-Fi dongle, allowing for smart home integration. Download the Mr. Cool app, plug in the dongle, and follow the setup instructions for full control from your smartphone. Even if you’re not tech-savvy, the included remote provides all necessary functions to toggle between cooling and heating easily.


This installation turned out to be a transformative upgrade. The combination of step-by-step preparation and careful execution meant that, without professional HVAC installers, I could enjoy a climate-controlled garage. Persistence and patience, especially with attic work, paid off significantly.

A major part of the Mr. Cool system’s appeal is its DIY nature. With some tools and a bit of ingenuity, significant home improvements become accessible. Not only does this keep costs down, but it can also be a deeply rewarding project for any DIYer.

So, whether you’re looking to heat your garage in winter, cool it down in summer, or possibly do both depending on the season, the DIY Mr. Cool mini-split system is an excellent solution. I hope this detailed guide helps you through your installation process. Until next time, happy building, and stay comfortable! If you have any questions or need further assistance, feel free to drop a comment below. Don’t forget to like, comment, and subscribe for more DIY tips and tricks!

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