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

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How to Install a Mini-Split Air Conditioner

  • Turn off the electricity to the circuit.
  • 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.
  • 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.
  • Screw the mounting bracket to the wall, making sure it’s level.
  • Install the air-conditioning unit to the wall-mounted bracket. Pass the refrigeration lines and condensate discharge line through the hole in the wall.
  • 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.
  • 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.
  • 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.
  • Slide a brass nut onto a new length of copper tubing, then use flaring tool to flare the end of the copper tubing.
  • 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.
  • Set the outdoor condensing unit onto a level pad adjacent to the chase.
  • Use two adjustable wrenches to tighten the compression fittings on the refrigerant lines. Then wrap pipe insulation around each line.
  • Run weather-tight conduit from an outdoor electrical box to the condenser unit. Feed electrical wires through the conduit.
  • Run a length of nonmetallic electrical cable from the condenser unit through the hole in the wall to the indoor air conditioning unit.
  • Snap the cover onto the chase to conceal and protect the lines and cable.
  • Make all electrical connections at condenser and at air conditioner, then pressure test the system with nitrogen to 300 pounds per square inch.
  • Vacuum out the nitrogen, then open valves to release refrigerant into the system.
  • Turn on the electricity and test the air conditioner.

Tools

Tools & Materials

  • Torpedo level
  • Rotary hammer
  • Drill/driver
  • Adjustable wrench
  • Flaring tool
  • Wire stripper
  • Pressure gauge and nitrogen
  • Vacuum