DIY install of mini split AC system

I have a contract to sell my house, pending the installation of air conditioning. (Up here in New England, AC is not standard.) Since I will never use this AC, I want to do this on the cheap. It looks like we will need 3 mini split systems. I can have a pro install the units for me, but I can probably save ~$10k if I DIY. I'll get an electrician friend to do the final hook up to my breaker box, so I can be sure that everything is to code. But I'm considering doing the rest myself. Do any of you have experience or advice?

I did everything except the final condenser line hookup on a single head system. Really not that difficult. One thing to look out for that in many areas code says you have to have a power switch near each head. The heads are often powered from the condenser, so this requires putting in a switch for the condenser near the head. Not a big deal for me as it was a single head located near the breaker box, so I just caught the line from the breaker to the condenser. May be more complicated in your case. Also, given it is likely to be 220V, not a normal light switch.

You can save a ton though. Cost me just under 2k doing it myself, and I had no quote under 6k for full install.

Cl(VII) said:

I did everything except the final condenser line hookup on a single head system. Really not that difficult. One thing to look out for that in many areas code says you have to have a power switch near each head. The heads are often powered from the condenser, so this requires putting in a switch for the condenser near the head. Not a big deal for me as it was a single head located near the breaker box, so I just caught the line from the breaker to the condenser. May be more complicated in your case. Also, given it is likely to be 220V, not a normal light switch.

You can save a ton though. Cost me just under 2k doing it myself, and I had no quote under 6k for full install.

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Chris, what brand of system did you use? It looks like the Mr. Cool systems, though the name makes me cringe, are made for DIY. And was the evacuation/pressurization step a problem? That's what everyone seems to be scared of, but I assume that if you and I can run a Schlenk line, it shouldn't be too much of an issue for a chemist.

If you're installing a system that you're going to sell, and you don't care that you leave the next guy with a crappy system, then I suppose you're okay doing this on the cheap. If I was the guy buying the house from you and requiring you to put in an HVAC system, I'd just get you to knock money off the asking price and put in something worth having.

Working in the HVAC industry as a mechanical engineer, I know for a fact that the cheaper systems will give you trouble and make you wish you'd spent the extra money and gotten one of the better ones. They're worth it in the long run.

To answer your question (oops, almost forgot), if you don't know how to braze copper lines, test for leaks, or charge a system with refrigerant you'll need to hire someone. It's possible to read about it on the internet and get it right but still requires a few special tools. I suppose it just depends on how handy you are.

BDB said:

Chris, what brand of system did you use? It looks like the Mr. Cool systems, though the name makes me cringe, are made for DIY. And was the evacuation/pressurization step a problem? That's what everyone seems to be scared of, but I assume that if you and I can run a Schlenk line, it shouldn't be too much of an issue for a chemist.

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I got a Mitsubishi because I plan to live there for sometime, and that looked like the most efficient and reliable. As for final evacuation and pressurization, I paid an HVAC company to do that step...cost me a 1.5 hr service call, so under $200. I didn't have the right equipment handy, and I wanted someone to look over shat I had done too before I closed up the wall I ran the lines in. The Mitsubishi comes pre-charged with the refrigerant, so it is really a matter of pump down/leak test and open the valve to fill the system. With a multi-head system the amount of refrigerant will vary, so you may need a top off (over a pre-charged system) if your total line lengths exceed a certain amount.

I probably could have kludged something from lab equipment and saved the $200, but it was piece of mind insurance more than anything. With home improvements I try to do the carpentry, basic electrical, and general labor stuff; and kick the specialty stuff to the professionals. I'm about to redo a second floor bathroom, and I will do most of it, but I will pay for the final plumbing hookups to be done. The price of a second floor water (or worse toilet) leak is too high.

I also got around the line fitting problems by buying lines with of the correct length with the correct connectors in place. It saves from needing to cut the lines, flare them, etc. which requires some specific tools.

A friend just put one in his house.
He found an "installer kit" online that included a pump for <$100.

Said it was pretty easy. Worst part it lack of instructions as they expect a pro installer.
But if you can braze copper pipes and do the electrical, the rest is pretty easy.

DO, for your own safety and probable code alignment, put in a power cutoff next to the compressor outside.
You don't even need a switch - just a "plug" that opens/closes the power....pretty cheap insurance.

Mushtang said:

If you're installing a system that you're going to sell, and you don't care that you leave the next guy with a crappy system, then I suppose you're okay doing this on the cheap. If I was the guy buying the house from you and requiring you to put in an HVAC system, I'd just get you to knock money off the asking price and put in something worth having.

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I completely agree! I offered that to the buyers and they turned me down. Now I'm in the position of being incentivized to do the cheapest thing possible. There's no way I'm going to spend a dollar more than I have to. Pretty dumb on their part.

I installed about 90% of my Mitsubishi system and absolutely love its performance. I had built a new workshop and did plenty of internal wall bracing so that the outside support brackets were nice and solid. I had everything ready to go for an HVAC guy and did my own shut off box and wiring. He only had to hang the head unit and finish some things outside.

I found an internet supplier that had good prices on my unit and was located about 15 miles from my house- that saved lots of money on shipping. I think I spent about $3K on a system that I was quoted $8-10K by professionals.

Mitsubishi has a comprehensive selection of mounting accessories and I installed PVC trim on the outside of my shop in order to run their channel system that enclosed all the wiring/lineset stuff. If you are in a cold climate then you should consider getting a heating kit that keeps the condensation from freezing inside the unit. I also opted for the wall bracket mounting system in order to keep my unit above the typical snow level.