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Hi there, DIY Dad here! Continuing the 1st-floor Japanese room renovation.
The final task: installing the air conditioner. Tools and materials used u2014 air conditioner, pair coil, non-adhesive tape, VVF cable, insect-proof cap, outdoor unit feet, pipe sleeve, concrete blocks, level, vacuum pump, flaring tool, impact driver, hole saw, cutter, and spanner.
The unit being installed is one I moved from my previous apartment. Since this was DIY Dad’s first time removing an air conditioner, there was some anxiety about whether it still worked.
This Japanese room happened to have a dedicated air conditioner outlet, so the mounting position was already decided. I started by installing the backplate u2014 the bracket the indoor unit hangs on. Ideally the backplate should anchor into plywood backing, but this is a small 6-mat unit and the gypsum board alone should be fine.
The indoor unit is mounted with a very slight tilt u2014 imperceptible to the eye u2014 to encourage the drain water to flow in the right direction. Reverse slope means drain water may back up and drip into the room. I used the level to get the angle right while fastening.
u2191 Backplate installed
Backplate is in u2014 but there’s no existing penetration hole for the pipes and wiring. The previous owner evidently never used an air conditioner here, so a new hole through both the interior and exterior walls is needed. Drilling a hole straight through your own wall is not exactly an everyday experience u2014 DIY Dad found it exciting.
The question was: what tool to use? The wall layers from inside out are roughly: diatomite plaster u2192 gypsum board u2192 insulation u2192 siding. A wood-working hole saw should handle that, DIY Dad figured. Off to the home improvement store.
Quality hole saws are expensive. There were also what appeared to be core drill bits u2014 but those seemed designed for a different purpose.
u2191 Core drill bit?
So DIY Dad went with the budget hole saw instead u2014 a set with about 7 different blade sizes for roughly u00a51,000.
u2191 Budget hole saw set
u2191 Home improvement store price
One problem: the blade depth is only about 40mm u2014 not enough to punch through in a single pass from one side. But attacking from both sides should get the job done.
That’s all for today u2014 see you next time!
u270fufe0f Originally published: November 20, 2016 (former Seesaa blog) | ud83dudd04 Updated: May 7, 2026
2026 DIY Dad’s Update: The Complete DIY Air Conditioner Install Story
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Fusuma Replacement Paper Kits
Fusuma renewal is the fastest Japanese-room refresh u2014 paper, paste, and 2 hours.
Installing an air conditioner was one of the higher-difficulty tasks in this renovation. As a mechanical design engineer, the attitude of “once you understand how it works, there’s nothing to fear” helped a lot.
Tools and Materials Required
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Tatami Repair Materials (Amazon Japan)
Fresh tatami edges signal a well-maintained property u2014 tenants feel it immediately.
- Flaring tool (expands the copper tube end)
- Vacuum pump (removes air and moisture from refrigerant lines)
- Pair coil (copper pipe + drain tube bundled together)
- VVF cable (power wiring)
- Hole saw (wall penetration)
- Insect-proof cap and pipe sleeve
- Level and impact driver
Both the flaring tool and the vacuum pump were rented u2014 a few thousand yen per day each. Renting specialized tools you rarely need is the smart move.
Before Drilling the Wall Penetration Hole
The backplate marks where the center of the hole should go. Before drilling, confirm no diagonal brace (u7b4bu4ea4u3044, suji-kai) is located there u2014 piercing a structural brace reduces earthquake resistance. In practice, drilling from the interior side avoided all braces and wiring. Drill at a slight downward angle toward the exterior to prevent water backflow.
Flare Fitting the Copper Line
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Shoji Screen Paper & Repair Kits
Replace shoji paper every 3u20135 years u2014 it yellows faster than any other surface.
Clamp the pair coil end in the flaring tool and turn the handle u2014 the tube expands automatically. A poor flare lets refrigerant leak, so the unit won’t cool. Take your time on the first one as practice.
Vacuum Evacuation Determines Performance
At least 15u201320 minutes of vacuum pump operation removes air and moisture from the lines. DIY Dad ran 30 minutes. Skip this and the system underperforms or fails. Confirm vacuum on the manifold gauge before opening the refrigerant service valves.
u2744ufe0f Know the Risks Before DIY-ing Air Conditioner Work
Refrigerant recovery, flare fitting, and vacuum evacuation require specialized tools and knowledge. Air conditioner installation generally requires an electrical contractor’s license in Japan. When in doubt, consult a professional.
DIY Renovation Quote Review Manual
How to read, compare, and negotiate contractor quotes. This manual saved me u00a5800,000 on a single renovation project.
ud83cudfe0 More from DIY Father
15 years of landlord experience u00b7 3 apartment buildings u00b7 DIY renovations that saved millions of yen. Browse all articles at diytosan.com
