How to Install a Ductless Mini-Split

Why this matters

Mini-split installation is the bread-and-butter project for a modern HVAC service business. Single-zone systems run, 1-2 days labor. Crews who can do this efficiently bill out in margin. Bad installs are the #1 cause of mini-split early failure + customer dissatisfaction. This is the working procedure.

Pre-install survey

Before quoting, confirm:

• Mounting location for indoor head (wall, ceiling cassette, slim duct)
• Outdoor unit pad location + path
• Line set route + length
• Electrical: panel capacity, distance to disconnect
• Condensate drain path
• Customer's color/style preferences for line cover

Photograph proposed locations. Measure twice.

Tools

• Drill + 3" hole saw (for wall penetration)
• Reciprocating saw
• Standard HVAC manifold + vacuum pump + recovery
• Manifold + hoses rated for refrigerant in use (A2L-rated for 2025+ R-32 + R-454B)
• Flaring tool (manufacturer spec for residential ductless: precision flare matters)
• Torque wrenches (for refrigerant fittings)
• Tubing benders + cutters
• Insulation slip-on for line set
• Aluminum tape + UV-resistant duct tape
• Electrical: wire strippers + lugs
• Line set cover material (slim duct cover or PVC)
• Outdoor pad + base
• Mounting hardware
• Ladder + harness (depending on outdoor unit height)
• Helper for indoor head lift

Materials per installation

• Indoor head + outdoor unit (matched per manufacturer)
• Line set (1/4" liquid + 3/8" or 5/8" suction, pre-insulated)
• Communication cable (14/4 or 16/4 SOOW, per manufacturer)
• Condensate tubing (5/8" rated)
• Wall plate / line set sleeve
• Outdoor unit pad
• Disconnect switch + 240V cable
• Line set cover

Procedure

Step 1: Mount indoor head bracket

1. Verify wall studs OR add plywood backer for hollow walls
2. Mark bracket location: 6" minimum clearance above, sides per manual
3. Level bracket; screw into studs (typically 4-6 screws)
4. Tighten firmly

Step 2: Drill wall penetration

1. Locate hole position per bracket: typically lower-right of bracket
2. Confirm no studs in path (use stud finder)
3. Drill from inside with 3" hole saw, slight downward angle to exterior
4. Drill to exterior wall
5. Insert sleeve (PVC or wall pass-through)
6. Verify no insulation or vapor barrier interrupted

Step 3: Prepare line set

1. Cut to length (allow 12-18" slack at each end)
2. De-burr ends
3. Flare each end carefully with precision flaring tool - perfect flares prevent leaks
4. Slip flare nuts onto pipes BEFORE flaring (can't slip on after)
5. Check flare with mirror; cracks or deformities = redo

Step 4: Connect at indoor head

1. Lift head onto bracket (helper needed)
2. Route line set, communication wire, drain through wall sleeve
3. Connect refrigerant lines to head per manufacturer (torque per spec)
4. Connect communication wire
5. Connect drain hose (gravity slope outward)
6. Snap head into bracket
7. Apply foam tape around line set at wall penetration

Step 5: Run line set to outdoor location

1. Either through wall directly OR external line set cover
2. Slim duct line covers () clean up appearance
3. Insulate any exposed line set
4. Avoid sharp bends (4" radius minimum)
5. Avoid hot spots (above stovepipe, electrical)
6. UV-rated tape over insulation breaks

Step 6: Mount outdoor unit

1. Place pad on level, well-drained surface
2. 12-24" clearance from wall + obstructions
3. Bolt unit to pad with vibration isolators
4. Verify level (refrigerant pools, compressor + drain)
5. In cold climate: 18-24" off ground for snow + defrost meltwater

Step 7: Connect at outdoor

1. Connect refrigerant lines to outdoor service valves (torque per spec)
2. Connect communication cable
3. Connect 240V power to disconnect
4. Verify all connections secure

Step 8: Pull vacuum

1. Connect manifold to liquid + vapor service ports
2. Open both ports + pull vacuum to 500 microns
3. Hold vacuum 30+ minutes
4. Verify no rise in microns (no leak)

Step 9: Release factory charge

1. Open vapor service valve slowly with hex wrench (refrigerant flows into evac'd system)
2. Open fully
3. Open liquid service valve
4. Close service ports
5. Disconnect manifold

For line set under factory charge length: no additional charge needed.

For line set OVER factory charge: add refrigerant per manufacturer chart (typically 0.4-0.8 oz per ft beyond factory length).

Step 10: Energize + test

1. Confirm disconnect on
2. Breaker on
3. Power up; verify outdoor unit LEDs
4. Verify communication established (no error code)
5. Run heating mode 10 min, cooling mode 10 min
6. Verify temperature swing (cool blowing 50-55°F, heat blowing 95-105°F)
7. Listen for unusual noise
8. Check drain flow

Step 11: Customer briefing + paperwork

1. Remote control + app pairing
2. Cleaning + filter schedule
3. Common error codes
4. Warranty registration
5. Manuall service contract offer
6. Photos + receipts

Acceptance criteria

• No refrigerant leaks (post-charge leak test)
• All connections torqued + insulated
• Drain flowing properly
• Customer signed work order
• App pairing tested
• Warranty registered
• Customer briefing complete

Common pitfalls

• Bad flare: leaks within months. Practice; use precision flaring tool
• Wrong torque: undertight leaks, overtight cracks flare
• Insufficient vacuum: moisture left in system, freezes EEV
• Wrong line set length entry: too much/little refrigerant
• Bad drain slope: water in customer's wall or ceiling
• Wall not stud-found: head pulls out of drywall
• Bracket not level: head tilts, condensate pours wrong direction
• No line set cover: customer sees ugly insulation on exterior
• No customer briefing: support calls for "how do I use this"
• Forgetting communication wire: post-energization error code

Quality + warranty

Most manufacturers provide:

• 10-year compressor warranty
• 5-7 year parts warranty
• Labor warranty 1-2 years from installer (longer with authorized contractor)

To preserve warranty:

• Use manufacturer-approved parts + tools
• Document install with photos
• Register warranty (usually within 30-60 days of install)
• Customer signs warranty paperwork

Customer talking points

Post-install briefing:

1. "Set thermostat once + leave it - variable-speed adjusts to demand"
2. "Wash the filter every 1-3 months - pull, rinse with water, replace"
3. "If you see ice on outdoor unit, that's normal defrost cycle"
4. "Annual service maintenance is recommended - let's schedule it now"
5. "App works on iOS + Android - let's set it up"

References

• AHRI Standard 210/240
• ACCA Manual J + S + T (residential design)
• Manufacturer install manuals (Mitsubishi, Fujitsu, Daikin, LG, Carrier)
• NEC Article 440 (motor-driven equipment)
• Manuall internal: Ductless Multi-Zone System Design Reference, Mini-Split Annual Service