2021 MR Cool DIY Multi-Zone Mini Split AC & Heating System Install

Introduction: DIY Multi-Zone Mini Split AC Installation

Hey everybody, my name is Mike Montgomery and today I’m going to show you how I installed a DIY multi-zone mini split AC unit from Mr. Cool in my living room. Additionally, I installed a second receiver in my bedroom for added comfort. I would like to note that Mr. Cool provided the unit free of charge, but my goal is to keep this article candid and informative.

Preparing the Installation Site

Instead of installing the condenser directly onto the ground, I used a concrete slab as a base. First, I mixed up a bag of fast-setting Quikrete and filled a form with it. After laying down a layer of half-inch rebar reinforcement, I screeded the concrete flat using a straight 2×4. After a few days, I removed the mold to reveal a functional, albeit rough textured, concrete slab.

Unboxing and Placing the Condenser

I then unboxed the Mr. Cool condenser and placed it onto the concrete slab. You can find out more information about this particular condenser and other equipment I used from Mr. Cool in the YouTube video description.

Installing the Indoor Units

Both the 24k air handler for the living room and the 12k air handler for the bedroom featured easy-to-use templates and brackets for installation. After marking the location of the hole to be drilled through the wall for the living room unit, I removed an old window unit. With the help of Josh and Jeremy, professional HVAC technicians, we installed both brackets securely to the wall.

Drilling Holes and Routing Line Sets

We then drilled holes through the exterior walls for both units, making sure to avoid hitting any studs. Once the holes were drilled, we prepped the indoor units by straightening out the line sets and feeding them through the holes. We also wrapped the lines with insulating tape for added protection.

Feeding the units and connecting the brackets went smoothly, and we made sure the line sets would be easily accessible for connecting to the condenser.

Connecting the Indoor Units to the Condenser

With both air handlers installed, it was time to connect them to the condenser outside. The Mr. Cool DIY system features pre-charged, quick-connect line sets, which made the installation process simple and straightforward.

We then connected the electrical wiring for both units, using color-coded wires and clear labels to ensure proper connections. The 24k unit required a line set adapter kit, while the 12k unit did not.

Jeremy, an experienced electrician, assisted in running a 220-volt line from the breaker panel to the condenser. After connecting all necessary electrical components, we tested the system by running it on its coldest setting for five minutes and then on its hottest setting for another five minutes. Everything worked perfectly, and the temperature dropped significantly within minutes.

Installing Drains and Finishing Touches

Before wrapping up the installation, we created custom copper drains to catch water condensation from the indoor units. We temporarily used a PVC pipe and gravel to create a French drain, but future plans include watering a garden bed with the collected water.

Lastly, I installed some cedar fence pickets to create a cover for the excess line set outside. With the garden beds finished, the project was complete.


I am extremely pleased with the results of this project. The new Mr. Cool multi-zone mini split AC unit is not only efficient but also provides flexibility for cooling different areas of my home. The smart thermostat and mobile app add convenience and ease of use.

While the installation process may seem daunting to some, it is entirely manageable for DIY enthusiasts. Moreover, hiring a professional to assist in certain aspects, such as electrical work, can still result in significant savings compared to a full HVAC installation.

Thanks to Mr. Cool for providing the unit and helping me upgrade my home’s comfort level. I’m excited to see how much my energy bills will decrease with this efficient system in place.

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