How to Install a Ductless Mini-Split AC
Mount an indoor air handler, drill a wall penetration, run line sets to an outdoor condenser, pull a deep vacuum, and wire the mini-split system.
- Read the tools, materials, safety notes, and steps below for free.
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- Allow camera and microphone. Point your phone at the work; the coach watches your progress and tells you the next step.
🧰 Required Tools & Equipment
- ✓ Cordless drill with 3-inch hole saw
- ✓ Torque wrench with crowfoot adapters
- ✓ HVAC manifold gauge set
- ✓ Two-stage vacuum pump
- ✓ Digital micron gauge
- ✓ Torpedo level
- ✓ Wire strippers and screwdriver set
📦 Materials & Supplies
- ✓ Mini-split indoor and outdoor units
- ✓ Refrigerant copper line set with flare nuts
- ✓ Condensate drain hose and line wrap
- ✓ 14/4 stranded shielded communication wire
- ✓ Condenser ground pad or wall bracket
- ✓ Nylog blue flare sealant
⚠️ Safety Checkpoints & Warnings
- • Shut off main electrical power at the breaker panel before stripping or connecting high-voltage disconnect wiring.
- • Verify no hidden electrical wires or plumbing lines exist inside the wall path using a reliable multi-scanner before using the hole saw.
- • Wear safety glasses and gloves when handling service ports to prevent cryogenic refrigerant burns.
- • Verify system pressure drop decay under vacuum before cracking open the refrigerant valves.
📋 Step-by-Step Guide (6 Steps)
Mount the Indoor Mounting Plate
Position the metal mounting bracket on the interior wall at least 6 inches below the ceiling. Use a torpedo level across the top edge and mark the screw holes into wall studs. Drive heavy-duty wood screws through the bracket into the studs, ensuring the plate remains perfectly horizontal.
- • Metal bracket firmly screwed flush against the drywall
- • Bubble resting dead-center in the torpedo level on the top lip of the bracket
- • Mounting the bracket out of level, which causes condensate water to overflow inside
- • Relying solely on drywall anchors without hitting at least one structural stud
Drill the Line Set Wall Penetration
Locate the knockout port on the mounting plate for the line set and mark a 3-inch circular hole. Chuck a 3-inch hole saw into your drill and drill through the interior drywall and exterior siding with a continuous 1/4-inch to 1/2-inch downward pitch toward the outside. Insert a plastic wall sleeve into the hole.
- • Clean circular 3-inch hole passing entirely through exterior siding
- • Visible downward angle when looking through the hole from inside to outside
- • Plastic sleeve seated flush in the penetration
- • Drilling flat or upward, which forces condensation back into the interior wall
- • Hitting exterior framing members due to misaligned template measurements
Hang Indoor Unit and Route Lines
Carefully unbend the copper piping stubs behind the indoor head unit to exit through the wall hole. Bundle the copper pipes, drain hose, and 14/4 communication wire together with vinyl tape, placing the drain hose at the absolute bottom of the bundle. Lift the air handler, feed the bundle through the wall sleeve, and snap the top hooks of the unit firmly onto the mounting bracket.
- • Indoor air handler clicks flat and secure onto the mounting plate
- • Line bundle protrudes smoothly through the exterior wall opening
- • Condensate drain sits at the 6 o'clock position in the bundle
- • Kinking the copper stubs while bending them straight back
- • Positioning the drain hose above the copper lines, creating an air lock
Connect Flare Lines to Outdoor Condenser
Place the outdoor condenser on a level equipment pad and run the copper line set to the service valves. Apply a drop of Nylog sealant to the flare face and threads, align the flare square with the brass fitting, and hand-thread the flare nut until seated. Tighten with a torque wrench using crowfoot adapters to the manufacturer's exact torque specification.
- • Flare nuts fully seated against the brass service ports with no exposed threads
- • No visible twisting or distortion in the copper lines adjacent to the nuts
- • Overtightening the brass flare nut, which cracks the copper flare flare face
- • Cross-threading the brass nut by using a wrench before hand-threading
Evacuate Lines with Vacuum Pump
Connect the manifold gauge and digital micron gauge to the outdoor unit service port and vacuum pump. Open the manifold valve and start the two-stage vacuum pump, running it until the micron gauge drops below 500 microns. Close the manifold valve, turn off the pump, and perform a 15-minute decay test to confirm the micron reading does not rise above 1000 microns.
- • Digital micron gauge displaying a steady reading below 500 microns
- • Micron reading stabilizes during the 15-minute valve-closed decay test
- • Relying only on analog compound gauges instead of a true digital micron gauge
- • Turning off the pump before closing the manifold valve, which pulls pump oil into the line set
Release Refrigerant and Finalize Wiring
Remove the brass valve stem caps on the outdoor service valves. Use a 5mm hex wrench to fully open the suction and liquid service valves counter-clockwise until they stop, then reinstall and torque the caps. Connect the 14/4 communication wire matching terminals 1-2-3-Ground between indoor and outdoor units, secure the line covers, and turn on the circuit breaker.
- • Valve stems fully backed out and solid brass hex caps torqued tight
- • Terminal block wiring matches identical color-to-number configuration at both units
- • Indoor unit power LED illuminates and blower wheel starts spinning smoothly
- • Forgetting to open both the liquid and suction service valves before power-up
- • Swapping wire terminals (e.g., placing wire 1 on terminal 2), causing communication fault codes
Credit: inspired by an original tutorial by alpinehomeair — watch the original on YouTube.
Don’t have everything?
- No Nylog blue flare sealant? A drop of clean POE (polyolester) refrigeration oil on the flare faces
- No Condenser ground pad? Heavy-duty exterior wall-mounting steel bracket secured to foundation studs
- No Crowfoot adapters? Dedicated digital adjustable mini-split torque wrench