How to Install a Ductless Mini-Split Air Conditioner

In this video, This Old House plumbing and heating expert Richard Trethewey explains how the pros retrofit a compact cooling unit.

How to Install a Mini-Split Air Conditioner

1. Turn off the electricity to the circuit.
2. Hold mounting bracket to the wall, level it, then mark the screw hole locations and where to bore a hole for the refrigeration lines, condensate discharge line and electrical cable.
3. From inside, bore hole into the block wall with rotary hammer and 3-inch-diameter masonry coring bit. Once the bit’s pilot penetrates the wall, finish boring the hole from the outside.
4. Screw the mounting bracket to the wall, making sure it’s level.
5. Install the air-conditioning unit to the wall-mounted bracket. Pass the refrigeration lines and condensate discharge line through the hole in the wall.
6. Attach a vertical chase directly below the hole in the exterior wall; the chase will house the refrigeration lines, condensate discharge line and electrical cable.
7. Extend the condensate discharge line down to within a few inches of the ground by attaching a length of PVC pipe. Secure the discharge line to the pipe with duct tape. Fasten the lower portion of the pipe to the chase by screwing on a metal C-clamp.
8. Carefully bend the copper refrigeration lines down into the chase. Use two adjustable wrenches to remove the compression fittings from the ends of the copper lines.
9. Slide a brass nut onto a new length of copper tubing, then use flaring tool to flare the end of the copper tubing.
10. Hold the tubing’s flared end against the end of the refrigeration line coming from the air conditioner. Hand-tighten the nut to hold the copper tubing to the refrigeration line. Repeat to attach the remaining refrigerant line.
11. Set the outdoor condensing unit onto a level pad adjacent to the chase.
12. Use two adjustable wrenches to tighten the compression fittings on the refrigerant lines. Then wrap pipe insulation around each line.
13. Run weather-tight conduit from an outdoor electrical box to the condenser unit. Feed electrical wires through the conduit.
14. Run a length of nonmetallic electrical cable from the condenser unit through the hole in the wall to the indoor air conditioning unit.
15. Snap the cover onto the chase to conceal and protect the lines and cable.
16. Make all electrical connections at condenser and at air conditioner, then pressure test the system with nitrogen to 300 pounds per square inch.
17. Vacuum out the nitrogen, then open valves to release refrigerant into the system.
18. Turn on the electricity and test the air conditioner.

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