When I first started looking into mini splits, the thought of installing one myself sounded intimidating. Cutting a hole in my wall? Running refrigerant lines? Hooking up electrical? Honestly, I almost called a pro.
But once I dug into the details, I realized that DIY mini split systems are designed for homeowners like me—folks who can handle basic tools, want to save thousands in labor, and aren’t afraid of a weekend project.
This is my complete step-by-step walkthrough of how I installed my DIY mini split system. I’ll cover every stage: from unboxing the unit to flipping the switch on for the first time.
🧰 Why I Chose to DIY Instead of Hiring a Pro
When I got quotes for a ductless mini split installation, I nearly fell off my chair. Local contractors wanted between $4,000 and $7,000 for a single-zone system. That included labor, refrigerant charging, and permits.
Meanwhile, a DIY system like the MRCOOL DIY Series was available online for $1,500–$2,000, and it came with pre-charged line sets that eliminated the need for specialized refrigerant tools.
For me, the math was simple:
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Pro install = ~$5,000
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DIY install = ~$2,000 (equipment) + $200 (tools/supplies)
Savings: over $3,000
And since I like projects, I figured I’d give it a go. Worst case, I’d call an electrician or HVAC tech for help.
📦 Step 1: Unboxing & Checking Parts
The first thing I did when the system arrived was unbox everything in my garage. A DIY mini split kit usually includes:
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Indoor air handler (wall-mounted unit)
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Outdoor condenser unit
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Mounting plate for the indoor unit
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Pre-charged refrigerant line sets (15–25 ft standard)
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Wall sleeve for the line set hole
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Communication cables
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Remote control
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Installation manual
Before I touched a drill, I made sure every part was accounted for. Trust me, you don’t want to get halfway through an install only to realize you’re missing a bracket or cable.
👉 The U.S. Department of Energy recommends always reviewing the manufacturer’s installation manual before starting.
🛠️ Step 2: Tools & Safety Gear You’ll Need
Here’s what I gathered before starting:
Tools:
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Drill + hole saw (3–4 inch bit)
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Level
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Stud finder
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Screwdrivers & wrenches
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Utility knife
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Caulk gun & exterior-grade sealant
Safety Gear:
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Safety glasses
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Work gloves
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Ladder
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Dust mask (for drilling exterior walls)
Mike’s tip: “Lay your tools out on a bench before you start. Saves countless trips back and forth.”
🖼️ Step 3: Mounting the Indoor Air Handler
The indoor air handler is the sleek wall-mounted unit that delivers the cool (or warm) air.
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Pick the right wall. Choose a central spot in the room, at least 6 inches from the ceiling and away from direct sunlight or heat sources.
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Secure the mounting plate. I used a stud finder to anchor into studs, then leveled the plate.
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Plan the hole. The plate has a template where the line set passes through. Mark that spot before drilling.
I originally had mine 3 inches too far left and hit a stud—had to move it over. Lesson learned: measure twice, drill once.
🕳️ Step 4: Drilling the Wall Hole
This is the part that makes homeowners nervous—cutting a 3–4 inch hole in your wall.
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Use a hole saw at a slight downward angle so the drain line can naturally flow outside.
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Insert the provided wall sleeve to protect the refrigerant lines.
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Seal around the sleeve with weatherproof caulk.
🔗 Step 5: Running Line Sets, Drain Hose & Wires
This step was fiddly but manageable.
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Feed the refrigerant line set, condensate drain hose, and electrical wiring through the wall sleeve.
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Bundle them neatly with tape or a line cover.
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Keep the drain hose sloped downward to avoid water backing up inside.
Mike’s reminder: “Don’t force the line set bends. Kinks can kill efficiency and even damage your unit.”
🧱 Step 6: Mounting the Outdoor Condenser
The outdoor unit is heavier, so I had a buddy help.
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Place it on a concrete pad or wall brackets.
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Maintain 12 inches clearance from the wall and 24 inches in front for airflow.
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Bolt it down securely to minimize vibration noise.
I also used rubber vibration pads, which cut down the hum I’d heard at a friend’s house.
👉 Mitsubishi Electric emphasizes outdoor clearance as critical to system longevity.
⚡ Step 7: Electrical Connections
This part can vary depending on your system. Some plug into a 110V outlet; others require a 220V line.
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Connect the communication cable between indoor and outdoor units (color-coded wires).
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If a 220V circuit is required, hire a licensed electrician unless you’re comfortable working with breakers.
According to HomeAdvisor, many DIYers bring in an electrician just for this step—still cheaper than full professional installation.
❄️ Step 8: Connecting Pre-Charged Line Sets
This is what makes a DIY mini split possible.
Traditional systems require vacuum pumps and refrigerant charging. But DIY kits (like MRCOOL) come with pre-charged line sets sealed with quick-connect fittings.
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Attach the line set to the indoor unit.
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Connect the other end to the outdoor condenser.
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Tighten fittings with wrenches per manual instructions.
No refrigerant handling required—just careful tightening.
👉 Fujitsu notes that non-DIY systems still require pro refrigerant charging, so make sure yours is truly “DIY ready.”
🔌 Step 9: Powering On & First Test Run
Now comes the fun part—turning it on.
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Flip the breaker back on.
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Set the remote to cooling mode and listen for the outdoor compressor to start.
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Feel the indoor airflow. Cold air should flow within 5 minutes.
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Switch to heating mode to verify dual function.
I walked around with my hand over the drain line outside to make sure condensation was flowing. Small detail, but it confirmed my slope was correct.
🧽 Step 10: Clean-Up & Final Checks
Before calling it done, I ran through this list:
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Sealed the wall sleeve with exterior caulk.
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Installed line set covers for a cleaner look.
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Cleared tools and checked for leftover screws (my golden rule).
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Double-checked system ran in both heating and cooling.
✅ Mike’s Final Installation Checklist
Here’s the quick reference list I use:
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Indoor unit level and secure
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Wall hole sealed and weatherproofed
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Outdoor unit clear of obstructions
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Line sets connected and no kinks
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Drain line angled properly
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Electrical wiring secure and breaker tested
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System runs quietly in both modes
👉 For long-term care, follow Energy.gov’s maintenance guide on filter cleaning and coil checks.
📊 Final Thoughts: Was DIY Worth It?
In my case—absolutely. The project took me about 6 hours spread across two days, mostly because I was double-checking each step.
I saved thousands in labor, learned how my system works inside and out, and now have the confidence to maintain it myself.
That said, if you’re not comfortable with electrical work or cutting into walls, don’t be afraid to bring in help for those steps. Even partial DIY saves a ton compared to hiring a contractor for everything.
For me, installing a DIY mini split was one of the most rewarding home projects I’ve done—and now, every time I adjust the remote, I get a little reminder: I put that in myself.
In the next topic we will know more about: How Much Does a DIY Mini Split Cost in 2025? Equipment, Labor & Energy Use Explained
