Hey Kev – How to Mini-Split Install

I’ve known of, but never fully realized the sheer awesome power of the fully functionally Mini-split. In a past house I cut a hole in the wall and installed a massive 24,000 BTU window unit AC thing trying to cool a house. The house was almost cool, but the sound level was equal to a Metallica concert. When we moved into the Shed a few years ago and tried to survive a summer we ended up with two 12,000 BTU window units in a window. Again we were mostly cool, at the cost of concert level volumes.

Since then I’ve gained more confidence working with automotive AC systems and finally have a rudimentary understanding of how they work. Michelle’s parents were going to stay in the shed for a while after Roxi came home from the hospital and I didn’t want them to melt in summer heat, or go deaf from sound. I bit the fear bullet and ordered a Sharp 18,000 BTU mini split with 25′ line set to install in the shed for them, and to heat / cool the place for momma when she uses it as her office.

After the install was finished and I pressed the sweet glorious cool button, I stood there in awe at the massive cold air flowing from the inside unit that was making next to no sound at all. I was shocked how quiet and effective these min split things are. I’ve been Kicking myself in the face since, for not getting over my fear of installing these things and getting them in previous houses. – They make hot and cold, are cheap to operate and quiet to live near – Why did I not get more sooner?

As soon as the shed unit was installed I ordered a 36,000 BTU Sharp unit for the house. Comfortup, who sold the unit via amazon stopped carrying the Sharp unit promptly after I clicked buy it now. They offered to replace the Sharp unit with a GREE unit with more SEER for the same cost. I took them up on the offer. A short while later the big 36,000 BTU Gree unit with line set and 14-gauge interconnect wire showed up at the house wrapped in black plastic. I spent a few hours a day for a few days and installed it in the house. The cold dried air perfects the summer feel of the house. It keeps the place at 50% humidity and 70 degrees of pure awesome comfort. With next to no sound at all. It makes less sound then the fridge makes.

Basic install

The mini split install, in my mind, is a five step / piece process, as follows:

  1. Mount the inside unit by setting the metal plate thing on the wall and drilling one or two holes in the wall
  2. Pour some concrete, make a pad, use brackets, ETC = mount the outdoor unit on stable thing
  3. Plumb 2 cooper lines, and a 4/14-awg wire between inside and outside units
  4. Wire 220 to the outside unit with a disconnect near the unit
  5. Vacuum pump the copper lines for half an hour, make sure no leaks then charge the system.

Every mini-split I shopped for came pre-charged with enough r410a to fill 25′ of supply line. To avoid expelling or adding refrigerant to the system I made sure the inside and outside components were 25′ apart. You can find online, or in the case of the sharp unit directions, precise math to calculate the amount of refrigerant to add or remove from the system based on line distance and size. For me I took the simplest path possible and made the units were 25′ apart. I like path of least resistance.

Mount the inside unit

The inside unit of the 36,000 BTU unit required 2 holes in the wall, the 18,000 BTU unit required 1 hole in the wall. The holes are for the copper supply line, 14-awg interconnect wire, and the water drain line. The 36,000 unit had the supply and drain lines opposite sides of the unit / hence the two holes. The holes are about 1 1/2″holes. The unit itself comes with metal plate on the back it hooks to. You remove the metal plate and mount the metal plate on a few studs. After you mount the plate, drill holes for wires and pipes, then stuff the things through the holes, hook the unit on the plate and you’re done.

Well you might want to seal the holes on the outside of the house too, but that’s later down the road once you’re outside again and know it all works.

Mount the Outside unit

The sharp unit sitting on a pallet waiting to be mounted on the small concrete pad Maddex and I poured for it

Big unit on a pallet, and big unit mounted on concrete next to the Daikin Air to water radiant floor heat pump. Looks small but it’s 190# thing.

The mounting is not difficult. You need to make a solid durable surface to mount the unit to. I’m obsessed with concrete, so my choice is to pour concreate pads, and bolt the units down to the concrete. The pads for the units used about six 80# bags of quickcrete. I went lazy and mixed them in a wheel barrow one bag a time. Is that really lazy? Not sure – but it was simpler for me to do then setup the cement mixer to use.


Don’t mind the weeds and need for landscaping. You can see the wires and hoses attached to the wall

I used 1″ metal conduit strap things to attach pipes and wires to the wall. The key here is to not crimp the copper pipe when bending it. You must make sure all of the bends are clean, without crimps. I went to harbor freight and picked up a 20$ tube bender kit and used the snot out of it on all of my bends. No crimping took place during my install. Some installers will run all of the lines in basically a down spout pipe to make it look prettier and be more protected. I’m not 100% into pretty and perfect finish when I build things.

I’m planning to put some concrete blocks behind the outdoor unit and better protect the line set from the kids when I find a round tuit. For now the line is in a 3″ pipe and covered with steel spikes to keep it in place and discourage kids.

Wiring the things

Wires hooked up the inside wall mount unit, and the new disconnect on the wall above the Daikin disconnects.

The wiring is not super complicated, but it can be intimidating if you’re not comfortable with wiring. The unit directions will tell you how big to build the circuit in amps. You need to size the wire and breaker for the max draw of the system, not the average draw. The 18,000 BTU model required a 30 amp circuit with 10 gauge wire, and the 36,000 BTU unit needed 40 amps with 8-awg wire. Both units require a service disconnect outside next to the unit for service. I bought a 6$ disconnect at Home Depot for the big unit, and smaller unit I mounted next to a 220 plug we used for an oven previously. A plug is a disconnect, and the stove is a 30-amp circuit, so I stuck an oven pig tail on the unit and plugged it in – done.

The 14-gauge wire between the inside and outside units does not require a disconnect based on NEC 2014, but you never know what your local peeps need, so make sure to check local building codes. The upside and outside unit interconnect blocks should be marked 1, 2, 3 and G or there abouts. Match the colours inside and outside and hook things up. Pretty simple. The 220 takes 2 hot wires and a ground – those should be marked the same.

Vacuum pumping and Charging

Harbor freight automotive gauge set, hooked up the inlet of an old school air compressor, and plumbing rough-in

I already have an automotive AC gauge set I’ve used working on cars. I bought the gauge set from harbor freight. Again, for cars I already had the fitting to hook the gauges to the air compressor to use it as a vacuum pump. What I did not have and needed to buy was a 5/16″ female quick coupler with ¼” flare. The coupler was needed to attach my gauges to the evacuation port on the outside unit thing. I bought coupler doohickey from amazon for about 14$, free shipping with no tax.

From here it’s pretty gosh darn simple. Red hose to coupler thing to the evacuation port on the compressor. There is only one evacuation port, and the coupler only fits on one hole so not much you can do here to screw it up. Blue hose on the gauge set to vacuum pump. You can use a compressor like I did or buy a pump from somewhere like harbor freight for 50$ or so. I ran the pump for 30 minutes each time until gauges were max level below zero. Then I shut off the knob for the blue gauge, shut off the pump and walked away for a bit. When the needle did not move back to zero I figured I’d won and the system was sealed.

On the 18,000 btu unit the gauge went back to zero when I came back to it. I went around to the fittings on the supply lines, tightened them a bit and tried again. Winning, pressure held this time. Next shut the red gauge, and remove the coupler from the evacuation port. The ports work like a car inner tube you have to push the middle thing to allow air in and out so push in hard as you loosen the coupler then pull it away super-fast to avoid a change in vacuum in the lines.

Now you’re ready to charge the system. Remove the caps facing out on the little fitting and the big fitting. Inside of those you will find Allen wrench holes. Stick in the right size Allen wrench in the hole and turn anti-clockwise until you hit resistance. The nuts will not come out, they will stop eventually and lock in the full open position. As you are turning you’ll hear the system charge. Put all of the covers back on and you’re done.

Go turn the power on, use the remote inside to turn on the unit and bask in your cold air; yippie!!

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