How To | DIY Ductless Mini Split Install | AC System

In this article, you will learn how to do your own DIY Ductless Mini Split Install. I have this beautiful shed on my property that really isn’t being used for anything other than misc. storage for odds and ends. It’s such a shame because it is more like a tiny house than a regular shed. With that, I’ve decided to turn it into guest quarters so that when somebody want to stay here, they will have their own accommodations and space. Of course with it being Texas, the first thing that needs to go in to make it habitable is some sort of AC system. 

With the space being pretty small….only 168sqft….I’m going with the only Do it yourself mini split system on the market currently, made by a brand called MRCOOL.

I started by cleaning out a walking path and work area on the wall where I’ll be mounting the inside unit which is called the air handler. I then took some measurements to make sure the unit would fit. I used a stud finder to locate and mark the studs inside this back wall then removed the bracket on the backside of the air handler and started predrilling holes for mounting it.

When placing this bracket, I lined up one column of holes to be in line with a stud. This, however, leaves the other side shy of the next stud. So with one screw holding the bracket in place and a level on top, I predrilled the hole locations for the second column of screws that wouldn’t hit a stud. This way I could remove the single screw I placed in the bracket, and tap in some wall anchors. I made sure these were flush then remounted my bracket. 

Next I started lining out where I needed to drill a hole in the wall for the plumbing that will connect the inside unit, to the outside one. These units are supposed to come with a template but I wasn’t able to locate mine. No problem though. I measured over from my left row of holes 6.5” and made a mark, then I found a circle that was 3 1/2” in diameter and traced round it.

Tip: you can punch a hole in the center so you can line it up perfectly to your pencil mark. To cut this out, I could have used a whole saw…but I didn’t have a 3.5” bit, so I went with a jigsaw instead. I used a drill bit to punch a hole big enough for my blade to fit in, then neatly cut around my pencil mark.

That takes care of my inside hole, now to transfer the center hole to the outside so another circle can be cut that’s inline with it. If you have a bit long enough to go through the entire wall then you can make this hole when you drill the inside center hole. If you don’t then re-find center of the hole and then punch through to the outside. I again used my 3 1/2” cap to trace a circle on the wall then cut it out with a jigsaw. 

With the hole cut all the way through, I took the plastic sleeve that comes with the unit and test fitted it. They come long so they can fit through a variety of wall thicknesses so I made a mark on where mine needed to be cut down, then used a jigsaw to cut it down.

I placed this in the inside hole, then capped it off on the outside. Now I have a smooth passage for the plumbing of the unit to pass through the wall. 

So the thing about mini split systems is they are pretty simple to install but most require equipment to charge the refrigerant lines. The MRCOOL unit though comes with the line set (this long white line) already charged for you. This makes the unit DIYable, but it also means that it comes with a stock length of line that can’t be cut down. So keep in mind when you are picking out your location for it that you’ll need to coil up and store any excess line. 

Once I fed through the start of the line set, I paused to also feed in the drainage line. This will drain off any condensation and moisture the unit creates. I push one end through the wall then connected the other end to the back of the unit, making sure to give it a few tugs and make sure it wasn’t going anywhere.

Oh also, it doesn’t say it in the instructions but there is a plastic corner cap on the backside of the unit that you need to remove. You can see with this piece gone, the line set has a lot more breathing room. 

Now, this part can be done with a single person, but having a second set of hands are makes things go easier. My mom was around and offered up hers. She got on the outside of the shed and pulled the line as I was on the inside feeding it through. There are rigid hard lines inside this white casing and it’s important that you don’t kink them. Take your time especially if you’re going up a ladder to get this entire line through smoothly and the unit set up on the wall.

Once you get close, it’s incredibly simple to get the air handler on the mounting bracket as it has a lip you can set it on then let it hang. Once the top is hung, you need to make sure the bottom is lined up, with the line set being inside it’s space, then push on it until it snaps into place. 

The inside is done, so next I moved outside to get it wired in. I’m comfortable tackling the simple wiring on my own so I pulled the covers off the unit and started by wiring in a power line.

I purchased outdoor flexible conduit called Liquid Tight and it came with a 90 degree fitting on one end with a straight fitting on the other. It also already had wires routed through it which prevented me from having to buy a power cord and fish it through.

This meant I just had to strip the ends and crimp on some spade connectors to get it all connected.

In the other knock out, I placed a grommet to protect the line from the sharp metal, and ran in the wiring from the line set. This comes with a connector already wired on for you. 

Now that I had both of my lines routed through the fitting, I started terminating them.

I first connected the power line, which are the ones with the little spade connectors. This was as simple as backing off of the screws, clicking the colors in the correct locations and then tightening down on them.

Then I connected the output line, which is that simple snap together connector already attached for you on the line set.

And that’s it. So I pushed everything inside so I could close the cap and reattach it with the screws using one of the comfy grip screwdrivers that came in the Husky 15 piece set I received through The Home Depot ProSpective tool campaign. These hand drivers all feature a very comfortable rubber handle and square shaft allowing you to turn it with a wrench for stubborn applications and also have the size of the drivers clearly marked on the ends of the handle.

I moved my unit down to the corner of my building so that it would open up the back to not only better airflow, but all give me a good sneaky spot to coil up my extra line set and stow it away. Be sure to consider how the outside will look when you are picking out the placement for the inside. 

For power, I will be running it off a quiet generator that will be stowed in this little cranny of the building. However, instead of plugging directly into the generator, I first wired in a fused disconnect box. This has a fuse which adds in a layer of protection between the unit and the power source so if there’s trouble, the fuse will trip first before damaging the unit.

After mounting the box I used one of the bottom knock outs to wire in the other end of the power cord that runs to the outdoor unit. Finally on the remaining knock out I purchased a heavy duty extension cord, cut off the female end, striped back the ends, and wired it in. I didn’t leave a ton of cord length here because the generator will be right in this spot. 

One of the final steps was to try and blend in the line set to the side of the shed. I found this race way material specific for line set at a local HVAC shop. It was hard to find one that sold to the public so if you have trouble I know there are similar products you can purchase through Amazon. 

Once I tidied that up and knew the unit wasn’t moving, I finally connected the line set to the unit. With these lines being precharged, you can’t disconnect these lines once you connect them, or you’ll have to get a professional out to recharge the lines. So before removing the protective caps and making these connections, just make sure the unit is where you want it to be. 

Overall this was so easy to do. Like all jobs, the final step is all the clean up. If you’re anything like me, I really appreciate having all of my tools returned to their place after I use them. To help with this effort, I’ve Been leaning on these handy little tool bags. They serve perfectly for little jobs like this one where I’m not working in my shop and away from my main tool box. This smaller one works perfectly for miscellaneous hardware while the larger one actually comes with a dedicated laptop compartment.

If you’re looking to install a mini split system, then I hope this video helped you out. Also, if you’d like links to anything used in the video then please check out the items below. Thanks for watching 🙂

Things I Used In This DIY Ductless Mini Split Install Project:

MRCOOL Mini Split
ISOtunes Bluetooth Hearing Protection
Stud Finder
Liquid Tight Flexable Conduit
Wire Strippers
Spade Connectors
Crimpers
Fuse Disconnect Box
Race Way
Woodpeckers Speed Square

(Most of the links listed above are affiliate links. As an Amazon Associate I earn from qualifying purchases.)