How to Install a MrCool DIY Mini Split Heat Pump

This thing is genuinely easier than most DIY projects I’ve done. No vacuum pump needed, no refrigerant charging, no special tools you don’t already own. If you can drill a hole and turn a wrench, you can install this yourself. Here’s exactly how.

• MrCool DIY mini split kit (indoor air handler + outdoor condenser + line set)
• Cordless drill and 3½” hole saw
• Screwdriver (Phillips)
• Adjustable wrenches (two)
• Level
• Tape measure
• Soapy water in a spray bottle
• The included USB dongle and mounting plate

Open the indoor unit box and grab the cardboard mounting template. It shows exactly where the mounting plate sits and where the 3½” hole goes to its right.

Hold the template on the wall where you want the unit. Make sure it’s level. The top-center screw of the bracket needs to hit a stud. The big hole on the bottom right needs to avoid studs, electrical wires, plumbing — anything you don’t want to drill through.

Mark the screw holes with something pointy (a screwdriver works). Then mark the center of the 3½” hole. Push a little dent into the drywall — it makes lining up the hole saw way easier.

Back at the indoor unit box, pull the air handler out. There’s one screw holding the mounting plate to the back of the unit. Remove that, then unclip the bottom tabs that hook the plate on. The plate comes off completely.

Take the plate and screw it to the wall using the provided screws. Center screw goes into the stud. Double check it’s level with your level. Also make sure the plate sits flat against the wall — no gaps.

Use a 3½” hole saw. Drill from inside out, at a slightly downward angle (about 2–3°). That downward slope is critical — it lets condensation water drain instead of pooling.

Once the hole is through, stick the wall sleeve into it. Mark where the sleeve pokes out the other side, pull it back, cut it flush with the wall, then push it back in for good.

Take the refrigerant piping, the DIY Pro cable, and the condensation line. Tape them together so the condensation line is on the bottom. This keeps water draining properly and makes the bundle easier to push through the wall.

Start by pushing the DIY Pro cable through the hole to the outside. Then grab the air handler and carefully feed its piping and condensation line through too. You’ll want a helper on the outside to receive all this.

Once the lines are through, lift the handler up and hook its top lip onto the top edge of the mounting bracket. Then push the bottom of the handler toward the wall until it snaps into the bottom hooks. That clicking sound means it’s locked.

Pop the USB housing off the underside of the front panel with a screwdriver. It’s just a clip. Unclip the USB port, plug in the dongle, clip it back in, and snap the housing back into place.

If you’ve got a 4th-gen MrCool, check the manual — the dongle location changed. Older models are as described.

Outside, put the equipment pad on level, stable ground. With a friend’s help, lift the condenser onto the pad. Position it so the line set can reach from its connection ports up to the air handler piping sticking out of the wall.

Uncoil only as much line set as you need to connect the two units. Do not kink it. Do not unroll extra. The line set is pre-charged with refrigerant, and kinking it can ruin the whole system. Take your time here.

Start by hand-tightening the matching connections (big pipe to big valve, small pipe to small valve). Then use adjustable wrenches to snug them up. Don’t overdo it — just snug. The manual has exact torque specs if you want to be precise, but hand-tight plus a quarter turn with a wrench is usually fine.

Remove the water tray from the side of the condenser (just unscrew it). Make sure the condenser’s service valves are fully closed before you start — they come closed from the factory, but verify. Remove the caps from the valve ends. Then hand-thread the line set nuts onto the valves. Use wrenches to snug them. Again, don’t go crazy.

Use the supplied MR Tool Allen wrench (or whatever fits) to turn the top valve counterclockwise until it stops. Do not force it. Do the same for the bottom valve. When you open these valves, the refrigerant trapped in the line set and the pre-charged condenser can now flow into the air handler. That’s it — the system is now charged.

If you’re installing a multi-zone unit, you might need to open the “king valves” too. Check your manual. For a single-zone, this step is complete.

Mix a little dish soap with water in a spray bottle. Spray every connection point you just tightened — both ends of both line set connections. If bubbles form, you’ve got a leak. Tighten the connection a bit more. If bubbles still appear, the manual has troubleshooting steps. But if you tightened things properly the first time, you should see nothing.

Put the sound-deadening pads around the connection joints between the line set and the air handler. Then wrap them with the provided tape to hold everything neat. This also prevents rattling.

Replace the water tray on the condenser.

MrCool says this part must be done by a licensed electrician. Don’t skip that. The electrician will:

• Shut off power to the unit (obviously).
• Remove the wire cover on the condenser.
• Unscrew the ring from the DIY Pro cable (turn counterclockwise).
• Pass the cable through the left-side hole in the metal panel, then reattach the ring to lock it in place.
• Connect the wires: terminal 1 to wire 1, 2 to 2, 3 to 3. The green neutral wire gets screwed into the green terminal on the plate.
• Run power from your house’s breaker panel to the unit.

Once that’s done, the system is ready to fire up.

Go inside. Point the remote at the unit and turn it on in cool mode. It should blow cold air within a minute or so. Run it in heat, dry, and fan mode too — five minutes each — to make sure all functions work.

If anything seems off, check the manual or call MrCool’s customer service. But honestly, if you followed the steps, it’ll just work.

That’s it. You installed a mini split. No vacuum pump, no refrigerant handling license, no special skills. Just a weekend afternoon and a helper who can lift.