Introduction: Install a DIY Mini-Split Air Conditioner / Heat Pump

Having a comfortably heated and cooled shop certainly makes working in humid summers and chilly winters a lot more pleasant. After limping along with an under-powered portable AC unit for our 2-car (22' x 30') garage shop, we finally decided that it was time for an upgrade.

After a little research, we came across the MRCOOL DIY Ductless Mini-Split Heat Pump which seemed a good fit being "DIY"! This unit both heats and cools and comes with a WiFi adapter which makes it possible to control with their smartphone app. There are also several sizes available for those with smaller or larger rooms.

Before we went down the DIY road, we did get a quote from a local HVAC installer for a slightly more efficient unit, but after seeing that it would cost over three times the price of the this unit, we decided that it was worth installing one ourselves. And since we purchased this unit ourselves (and have no affiliation with MRCOOL), we'll try to cover both its pros and cons.


Step 1: Unpacking the Condenser

The heat pump came in two boxes. The larger box is for the outdoor condenser unit which is usually placed on a small pad or installed on an exterior wall using a mounting bracket and then wired to a dedicated 120V or 240V circuit depending on the size of the unit.

In this box was the drain line extension, a plastic pipe, and a set of rubber pads to sit the unit on. There was also some neoprene putty and an Allen wrench.

Step 2: Unpacking the Indoor Unit

The second box contains the indoor unit which is mounted to an interior wall. Connected to it is a set of refrigerant lines and a power line that are run through a hole in the wall down to the outdoor unit. There's also a small drain line connected to it that carries off any condensation from the indoor unit.

The indoor unit box contains the user manual, filters, the remote control, a drain connector for the condenser, and the Wi-Fi adapter. It also contains a cardboard template for the mounting plate with the location of the hole that must be cut in the wall.

I carefully removed the indoor unit with the attached line set from the box. After removing the zip ties holding the lines together, I then removed the metal mounting bracket from the back of the unit and uncoiled some of the lines being careful not to kink them.

I very gently bent the lines so that they exited the back of the unit where the hole will be located. The shorter tube is the drain line and it needs to exit underneath the line set so that any condensation can easily drain outside.

Step 3: Installing the Mounting Bracket

Next I leveled and taped the template to the wall of our shop and pre-drilled holes on two stud locations. I also went ahead and drilled a pilot hole where the hole for the line set would go before attaching the mounting bracket to the wall with a pair of cabinet screws.

Step 4: Drilling the Lineset Hole

It was then time for the most stressful part of the installation -- cutting a large hole through the wall!

I started by drilling a hole through the interior wall using a 3.5" hole saw attached to my drill at a slight downward angle to help with drainage. Once I drilled through the interior wall, I cut a small hole in the insulation and continued drilling through the exterior sheathing which also made a pilot hole in the siding.

Since we have fiber cement siding I decided to finish cutting it from the outside to avoid any damage. This actually ended up working better than I expected using the hole saw and the end result turned out pretty nice.

We then inserted the included plastic pipe that protects the line set and trimmed off all but about 1/2" of the excess on the outside with a hacksaw and sanded over any rough edges along the bottom.

Step 5: Mounting the Indoor Unit

With the hole finished, I then completed attaching the mounting bracket with the remaining screws, and it was finally time to mount the indoor unit on the wall.

To keep from kinking the roughly 25 feet of line, my wife helped feed it through the hole from the inside while a friend of ours helped from the outside. The important thing to remember is that the drain line must be on the bottom when the lines are fed through. The unit then just hooks onto the top of the bracket and snaps down onto the bottom.

We did waste a little time here second guessing ourselves just because the wall wasn't perfectly flat, but other than that, the mounting was pretty easy!

Step 6: Sealing the Lineset Hole

Back outside I used some caulk around the pipe and then some of the included neoprene inside it followed by low-pressure foaming sealant. I then attached the drain hose extension and began work on the line set cover.

Step 7: Installing the Lineset Cover

The lineset cover sections are made of a back piece that is screwed to the siding and a front piece that is then screwed to the back piece. Because our siding slopes (overlaps), I bought a few packs of small nylon spacers from the local hardware store to insert behind the cover where needed when screwing it into the siding.

Then I continued down adding a connector piece which overlapped the previous piece about half an inch. I overlapped the next piece with the connector as well and then secured it to the siding.

Step 8: Securing the Lineset to the Cover

Once the back cover was installed, it was time to secure the lines to it using some zip ties and the included brackets that twist into place on the cover.

Step 9: Finishing the Lineset Cover Installation

Next, I snapped on the front sections of the cover and connected them with the small strap pieces. I also added a little caulk around the top of the cover before moving on to the condenser unit.

Step 10:

We decided to install the outdoor condenser unit on an existing concrete pad on top of two concrete blocks just to raise it off the ground a bit in case of the occasional snow storm. Instead of pouring a concrete pad, a hard plastic condenser pad could also be used.

Next, I inserted the rubber pads under the feet and mounted it to the concrete blocks with a few Tapcon concrete screws. I also went ahead and attached the drain elbow to help direct any water off the concrete pad.

Step 11: Attaching the Refrigerant Lines

To attach the refrigerant lines, I removed the cover on the side of the condenser and, after removing the caps, hand threaded the lines onto each of the connections. The connections are different sizes, so it was easy to know which went where, but you do have to be careful not to cross-thread the threads on the connectors. I then used a pair of adjustable wrenches to finish tightening everything to avoid damaging the connectors.

Step 12: Opening the Refrigerant Lines and Checking for Leaks

The reason for the "DIY" in the name of this unit is that the system is pre-charged and does not require a HVAC technician to complete the installation. To finish up with the lines I sprayed them with soapy water to spot any leaks and then removed the metal caps on the connectors and opened the lines with the included Allan wrench. After a checking for leaks one more time, I put the caps back on and then reattached the plastic cover.

Step 13: Completing the Electrical Installation

The not-so-DIY part of this mini-split is that an electrician is needed to run a new 120V or 240V circuit (depending on the unit) to the condenser. The wiring connection to the unit itself is pretty simple and the only other thing that needs to be done is to plug in the wiring harness from the indoor unit to the connector on the condenser and connect the ground wire.

Step 14: Testing the Heating and Cooling

Once the included filters were attached, it was finally time to test out the unit's heating and cooling ability. Both worked extremely well during the initial test.

We've actually had the unit for over a year now, and it has no problem keeping our workshop cool even on several 95F+ degree days with high humidity. It also worked well to keep the shop dehumidified and cool enough to work in when wearing a respirator and other safety gear. During the winter the unit kept our shop plenty warm even when the outdoor temperatures dropped to 35F or so.

We've definitely been impressed by what these units can do, but if you live in a really cold climate you may need a little backup heat on very cold days.

Step 15: Remote Control and WiFi

The included remote control works well and comes with a mounting bracket to give it a home. It is IR based, so you do need line of sight to use it.

To setup WiFi, I plugged in the included adapter and installed the MRCOOL app on my phone. Next, I used the remote to enter "AP" mode on the indoor unit by turning it on and pressing the LED button on the remote 7 times. Then after registering and logging in on the app, I added the unit to the app by scanning the included QR code.

To use the app, you simply click to power the mini-split on and then select the desired mode (Auto, Cool, Dry, Heat, Fan). You can then drag up or down to change the temperature and, if the mode allows for it, change the fan speed.

Note that the previous version of the WiFi app had issues losing the connection to the unit. Since MRCOOL released a new version of the app earlier this year, we have had no problems connecting to it every time and changing its settings.

Step 16: Pros and Cons


  • The biggest "pro" for most people will likely be the cheaper price vs. having an HVAC company install a unit.
  • WiFi connectivity is definitely nice for our application where we want to dehumidify the workshop or cool/heat it before going out to work in it.
  • Relatively quick install. The installation can be done in a few hours or certainly over a weekend.


  • Hearing everyone tell you that you forgot to flush/vacuum the lines. (This is not required for this unit! Feel free to direct them to the installation instructions. :) )
  • Cutting a hole through the wall. This is required for all mini-splits that I've seen, though some people get creative over hiding the lineset.
  • The extra lineset must be coiled up and placed next to the unit (preferably horizontally). Cutting it would require having an HVAC tech recharge/vacuum the lineset.

Step 17: Parts and Tools