How to Install a DIY Ductless Mini-Split AC
Mount, plumb, and connect a pre-charged DIY ductless mini-split heat pump system to provide efficient single-zone heating and cooling in your home.
- Read the tools, materials, safety notes, and steps below for free.
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🧰 Required Tools & Equipment
- ✓ Cordless drill with 3.5-inch hole saw
- ✓ Torpedo level
- ✓ Stud finder
- ✓ Adjustable wrench set (or open-ended wrenches)
- ✓ Wire strippers and screwdrivers
- ✓ Measuring tape
📦 Materials & Supplies
- ✓ Pre-charged mini-split kit (indoor unit, outdoor condenser, lineset)
- ✓ Condenser pad or ground mounting bracket
- ✓ Wall sleeve and protective plastic cap
- ✓ Expanding foam sealant or duct seal putty
- ✓ PVC line-set decorative cover kit
⚠️ Safety Checkpoints & Warnings
- • Turn off main circuit power at the breaker panel before touching electrical connections.
- • Verify no hidden electrical wires or plumbing pipes exist inside the wall cavity before drilling the 3.5-inch hole.
- • Use two people to lift and carry the outdoor condenser unit to prevent back injury.
📋 Step-by-Step Guide (6 Steps)
Install Indoor Mounting Plate
Locate wall studs using a stud finder and mark their positions. Place the metal mounting bracket against the wall at least 6 inches below the ceiling, verify level with a torpedo level, and secure it firmly into at least one stud using heavy-duty wood screws. Add drywall anchors for remaining mounting holes across the plate.
- • Metal bracket is screwed flush against the wall.
- • Level bubble rests dead-center between indicator lines.
- • Mounting too close to the ceiling, restricting necessary intake airflow.
Drill Wall Penetration Hole
Mark the 3.5-inch hole location based on your indoor unit bracket instructions (typically lower left or right). Drill a pilot hole straight through, then cut through the inner and outer wall using a 3.5-inch hole saw angled downward slightly toward the exterior at roughly 5 degrees for drainage. Insert the plastic wall sleeve tube from the inside out.
- • Clean 3.5-inch round hole visibly slopes downward to the outside.
- • Plastic sleeve sits flush on interior and extends slightly outside.
- • Drilling flat or upward, which causes condensation water to back up and flood interior walls.
Mount and Feed Indoor Air Handler
Gently bend the copper line pipes and condensate hose directly straight back behind the indoor unit. Bundle the line set, drain hose, and communication cable together with wrapping tape, placing the drain hose at the bottom of the bundle. Carefully feed the bundle through the wall sleeve while hooking the top of the unit onto the mounting plate, then press firmly until the bottom clicks into place.
- • Indoor head unit hangs level and firmly locks against mounting bracket.
- • All bundled lines exit through the exterior wall opening.
- • Kinking the copper refrigerant lines while bending them by hand.
Position Outdoor Condenser
Set an equipment pad or level concrete pavers on ground with good clearance (at least 12 inches from wall). Place the outdoor condenser unit onto the pad, ensuring rubber anti-vibration pads sit beneath each foot. Fasten the feet to the pad using stainless steel bolts or anchors.
- • Condenser stands level and stable on the pad without wobbling.
- • Rubber isolation pads are compressed evenly beneath all 4 mounting feet.
- • Placing the condenser directly on dirt or uncompacted ground, causing sinking over time.
Connect Pre-Charged Quick-Connect Lines
Uncoil only the necessary length of pre-charged line set without sharp bends. Thread the line set connectors to the matching condenser ports by hand first until snug, then use two wrenches to tighten down the DIY quick-connect couplers completely until the threads bottom out. Repeat for the matching indoor unit connections.
- • Hex nuts are bottomed out completely metal-to-metal on both ports.
- • No exposed thread remains visible on the quick-connect joints.
- • Cross-threading brass fittings by using a wrench before hand-tightening.
Wire Communication Cable and Seal Wall
Route the 4-conductor communication wire to the outdoor unit wiring compartment and connect color-coded terminals matching the numbered sequence (1, 2, 3, ground) used on the indoor head. Pack expanding foam or duct seal putty around the exterior wall sleeve opening to seal out moisture and insects, then snap on the decorative line cover channel.
- • Wires are clamped securely under color-matched screw terminals.
- • Wall sleeve exterior is fully sealed with waterproof putty or foam.
- • Decorative line hide cleanly covers outdoor piping bundle.
- • Mismatched wire color order between indoor and outdoor terminal blocks.
Credit: inspired by an original tutorial by DIY Creators — watch the original on YouTube.
Don’t have everything?
- No 3.5-inch hole saw? Reciprocating saw after drilling a perimeter of small pilot holes
- No Pre-poured condenser pad? Four heavy-duty 16x16-inch concrete patio pavers leveled on a gravel base