Down The DIY Rabbit Hole With A Shop AC Installation

There’s a fine line between a successful DIY project and one that ends in heartbreak. It’s subjective too; aside from projects that end up with fire trucks or ambulances in the driveway, what one DIYer would consider a disaster might be considered a great learning opportunity to someone else.

We’re pretty sure [Cressel] looks at his recent DIY mini-split AC installation for his shop as a series of teachable moments. Most folks leave HVAC work to the pros, but when you run a popular YouTube channel where you make your own lathe from scratch, you might be persuaded to give anything a go. [Cressel] did everything possible to do this job like a pro, going so far as to get training in the safe handling of refrigerants and an EPA certification so he knew how to charge the system correctly. He also sunk quite a bit of money into tools; between the manifold gauge set, vacuum pump, and various plumbing bits, that was a hefty $300 bite alone.

The install went well until he started charging the refrigerant, when a mistake with a fitting caused him to contaminate his nice, new batch of R-410A. Rather than back out and call a pro to finish up, [Cressel] stuck with it, to the tune of $900 in extra tools and materials needed to recover the old refrigerant safely and replace it with virgin R-410A. The video below has a condensed version of the whole tale.

It all worked out in the end, but at a cost that probably meets or exceeds what an HVAC contractor would have charged. [Cressel] seems like a glass-half-full kind of guy, though, so we expect he’s happy to have learned something new, and to have a bunch of neat new tools to boot.

50 thoughts on “Down The DIY Rabbit Hole With A Shop AC Installation

  1. If the problem was a mistake with a fitting, it could have happened to a pro also. The only difference is that the pro would have eaten the cost , or already have the tools to recover from the mistake. For the first time installation of someone, that $900 could be considered as a “learning fee”.

    1. There are plenty of contractors who won’t attend classes as part of their professional journey. They pass on their “learning fee” to the manufacturer via warranty expense. Parts changers rather than troubleshooters.

  2. If the first time doing a project involves things such as tools and training is that really part of the cost of the project? I guess if it’s the only time you use those tools and that knowledge/certification then it is. On the other hand if he intends to do a bunch more A/C work then it’s not really fair to count that as part of the project cost is it?

  3. I did a DIY mini-split. I wasn’t exactly DIY, i traded for the electrical work and the people that work on my whole house AC did the charging, I don;t think they even charged us since they were there for other work. I had called other AC people to charge this but they were very expensiveness. The AC people were great and were interested in it. I love the mini-split very quiet helps a room we run a business in that gets hot because of all the computers. I say go for it well worth it.

    1. But what fun is that? I try to keep a low ratio of “learning projects” to useful projects, but they’re still good to keep up your personal growth and fend off that existential pain with lovely, distracting curiosity.

        1. Note the smiley on [Gnomer]’s comment…

          If you physically turn a window air conditioner around, it will pump heat from outside and dump it in the room, in addition to the heat coming off of its compressor.

          In that sense, leaving the door open on a refrigerator also heats up a room.

          1. Except that in the refrigerator situation you’re only getting the heat from the compressor, no heat pumping is occuring because the cool is in the room too. I know you know that Ren, but others might miss the difference.

          2. Transfer of heat in any direction is only transfer of heat. Plus the electric caused by motors such as compressor and typically two fans.
            Give for fellow in video but that is a very expensive learning curve.

    2. Mini splits are super efficient, waaaay more than a window AC unit. That efficiency means that you can run the smaller ones off a 15 amp (220) circuit, which is way less power required of a window unit. Plus, mini-splits are heat pumps, so they can heat as well. A decent mini-split for a small space can be had for $600. By the time you get a decent window unit and heater, you’ve spent nearly that and don’t have nearly as efficient a system. Plus they are waaaay quieter.

      Also, most of them (all) come pre-charged, what you’re actually doing is pulling a vacuum on the lines. The only time you need to charge them is if you run really long lines, or spring a leak. I plan on adding one to my shop at some point, I can do everything but pulling the vacuum… I mean I could but I don’t care to but the equipment. My HVAC guy said he’d do it for me though for $100.

  4. Several years back I replaced an existing heat pump-based HVAC system in the house we had just purchased. The previous system was original to the home, over 10 years old, inefficient, and horribly undersized once an addition was built onto the house.

    I installed a heat pump outside and a matching air handler in the crawlspace with 20kW of emergency heat. I researched and learned all that I could. I built a riser for the heat pump unit to sit on due to snow that drifted, bent up new larger ducting for both the supply/return and sealed everything up with mastic and aluminum tape. I used mastic and giant zip ties for all the flexible duct connections. Dampers were installed at the base of each run so I could balance everything. I had saved myself thousands of dollars over what I had been quoted by multiple installers.

    Despite all that work and learning, I wanted to leave the charging of the system for a professional. This is where things got hairy and was something I had never considered… no one wanted to touch a system an amateur had installed. I kind of understand this after the fact, but it never crossed my mind as being a problem. It took months before I found someone willing to sweat the fittings on the refrigerant lines and charge the system with the R410A I had already purchased from an installer that bailed on me at the last minute. A family friend of my boss who owned/operated an HVAC business and had previously taught HVAC classes, ended up being the ONLY person willing to finish the job. He praised my work and said it was better than many professional jobs he had seen. The system has been running great ever since.

    If you intend to do this yourself and take the approach I did, have someone willing to finish the job lined up and committed BEFORE you start.

    1. Call for a repair and say “It was like that when i got here”, they would probably find that it only needs a charge… this is hard to do when they see a pile of tools and new fittings/pipes but it might sound better than indicating it was a diy job…

    2. I installed a full size split system, including new gas furnace. My problem was the learning curve on brazing the copper lines. I initially though it would be similar to soldering copper water pipe, but found out the R410A requires fittings that are brazed at a high enough temperature to require an oxy-acetylene torch and flowing nitrogen through the line while brazing. The learning curve was a bit steep, so I decided to hire out that part. I got lucky and found out the the luthier at the local violin shop was a former A/C tech. I loaned him my tools and paid him to finish the brazing and charge the system. His pipe bending and brazing work was a work of art.

      1. Same here – took on a furnace and ac system swap. Brazing and learning superheat/subcooling principles was the biggest part of the learning curve. Running a new lineset is kind of a pain in the butt to be careful to not kink it. Not too bad though if you pay attention to detail and read and research until you fully understand the install manuals of everything involved, and do some practice brazing on some scrap pieces (and pressure/vacuum test your trial runs on scrap). If you can find tools used from another DIY or HVAC tech getting out of the field, its not horrible to do. You can take an online EPA test to be certified to order refrigerant. My only advice would be ‘do it right’ and get a micron-level digital vacuum gauge so you can prove to yourself your brazing job was done well and holds a high vacuum before you go and try to charge up the system (which you should do anyway, but don’t just use a gauge set to do this).

    3. 4-10a is very hydroscopic and the least amount of time line set is open to atmosphere the better. Also the corrosion of the line set becomes a huge factor. It all needs to happen fast as possible. Keep end caps on all tubing, again be fast, possible rainy days are not recommended, put a very low positive (Dry Nitrogen) charge on the line set. If any braziing needs to be done. And absolutely make sure a filter / dryer is installed. Some units come preinstalled while others need field installation. And on I side note the videos stated how much refrigerant to use but that weight is for a given length of line set. So shorter will take less and of course longer will take more. Hope if helped

  5. If it’s a pre-filled split AC (and it looks like it is), then there is no need for extra tools or materials.
    All you need is to open and close the proper valves in the proper order, 2-3 times, as described in the installation manual. I installed mine alone in about two days of reading and another day of working.

    The Chinglish manual helped a lot. It was so unclear that it forced me to first spend a weekend online understanding about pipe bending techniques, filling procedures with or without a vacuum pump, common pitfalls, etc.

    Sometimes a Chinglish manual helps a lot by being bad, so bad that it makes one research the subject itself.

    1. You’re right, most mini-splits come pre-charged. You only need to charge them if you run lines in excess of the standard length. However, what you typically have to do is pull a vacuum on the system, which requires the special tools. There’s really no reason a HVAC person should charge more than $100 to do this for you, at least that’s what my HVAC guy told me.

    2. Indeed, the recommended method is with a vacuum pump.

      What I’m trying to say is mostly a hack which I tried on my own AC, and the AC worked fine for many years.

      It can be done without the vacuum pump. Without vacuum pump, the idea is to let the cooling agent to push most of the air outside of the pipes.

      To do that, release the agent and let a little bit to be expelled (together with most of the air present in the pipes) by pressing the other valve for a few seconds, e.g.:

      1. P.S. Wrong video, sorry.

        Forgot to tell that I did that hack only because it was in the middle of a heat wave, and all the qualified personnel was already booked for weeks. So, the last resort was to buy the cheapest AC and install it myself, the sloppy way, without a vacuum pump. I was hoping for the sacrificial AC to work at least until the autumn fall, yet it worked just fine for many years.

        It was a nice surprise.

  6. I recently installed a small Mitsubishi split AC – it came precharged so just needed to vacuum it out and open the valves. One thing I did learn is that when not using a condensate pump, the condensate drain needs a continuous fall all the way to avoid airlocks making it back up and leaking out the bottom of the unit.
    You can buy pipe sets pre-insulated with the flares already done to avoid the need for a flare tool – a vacuum pump is the only “special” tool needed.

  7. Better not let the guys on HVAC talk see this thread. They’ll chew this guy up into little pieces.

    Wondering if any factory warranties are still valid ? Usually the fine print stipulates that it must be purchased from an “authorized” dealer, and installed by a *licensed* contractor.

      1. What does that have to do with the factory warranty ? Dude calls up the manufacturer, “my compressor failed”. First question from the manufacturer will be: “well did you contact your authorized dealer?”. Said dealer should also be a state licensed contractor (LG, Mitsubishi, whomever, will want their information if said dealer is not in their system).

        No different than Sony (any of the major AV manufacturers), or JetCat (as another example), refusing to support “gray market” vendors selling their products.

        1. Lol your absolutely correct. To get EPA cert read a 12 Paige and fill in the abcd 30 question test. Every unit that a respectful contractor installs is certified. Amozon warriors usually have no way a warranty.

  8. I love using a project as a justification for buying tools, but this is just stupid. HVAC tools are incredibly specialized, and the only thing left to do with them after a project like this is to sell them. Also, he spent more on tools than the split system even costs. And yes, this may be a ‘DIY’ installation, but the system is just an off-the-shelf unit (prefilled with refrigerant!) and all he really needed was a vacuum pump (which is a neat tool to buy for other uses). But hey, gotta make that YOUTUBEMONEY I guess…

  9. I love re-purposing old A/C units. Here is the first one I did to heat my pool (a few years ago but still working today). I learnt loads hacking this first machine. I’ve since built units to heat and cool my house plus designed and built a fully functioning controller using an esp8266 with IOT etc…

  10. Interesting.

    I learned enough to be able to maintain and expand our home’s radiant heating system into a 3 zone system, and that’s been going strong for 8 winters now… but I thought that air conditioning would be just too hard… but it’s great to see that it can be done with study and patience.

  11. Robby say’s
    Every one say’s it’s straight forward to install an ac system, however, all you DIY Desmond’s have forgotten one very important element of an install – – no one ,but no one has bothered to prove their pipework is capable of holding pressure up to 41 bar! If your pipework dos’nt, you’re running the risk of losing that very expensive R410a, to atmosphere. Not withstanding the fact that you are risking losing all your refrigerant, but your compressors lubricant goes with it! Pop – need a new compressor. Just thought you might take that into account.

    1. It should be standard procedure but not often followed. Pressure test with nitrogen to max. working pressure + 10% – if you do the course for manipulation of refrigerant gases it’s part of the training. Personally I ALWAYS do this test (as well as a hacker I install professionally). Much cheaper a bit of Nitrogen than R410 (or whichever) that is currently 85 euros or more a kilo.

  12. The thing with HVAC and DIY is in many municipalities the building code and the cartel is against you. The cartel are the HVAC people and the manufacturers. If your system was not installed by a licensed contractor and you have issues down the road, good luck in getting the manufacturer to honor the warranty.

    The real bitch is that a lot of the licensed guys are morons. I got a high efficiency system installed and it took the guy over a month to get all the bugs worked out. He insisted it was very complicated. A year later the hot surface ignitor went out and I had another HVAC guy come out and he went over the system with me. It was brainlessly simple, and all the issues that I had with the unit were covered in the manual that came with it. The unit was also oversized for the house. The first guy licensed as he was, was still a total moron.

    I recently had a friend who was going to do his own HVAC install. He kept telling me how easy it was to do. His friend bought a smart thermostat for her place and asked him to install it and he starts writing to me with questions. Urg. In the end he found a guy to do the install for him, and it works well. IMHO unless you really have a burning desire to DIY, or you are putting a few of them in and you have a competent HVAC guy, it is going to better off long term to let him do it. If the guy is cool you can watch and learn, and in many cases you can do all the ground work to save a few bucks.

  13. One idea to increase A/C efficiency is to use ‘redneck geothermal’ air pre-cooling. That is, dig the deepest hole you can, then run ducting down to the bottom of it and back up to the A/C unit’s air intake. It is far from a complete solution and comes with multiple caveats of its own, but it will drop the temperature of the air entering the system by a few degrees, which will increase the unit’s overall efficiency.

  14. Over 40 comments so far and not a single mention of hydrocarbon replacement refrigerant!

    I’ve used the HC stuff for years because it doesn’t require a licence to use & buy. If you know your stuff, and use the right oil & fill quantities, there is absolutely no problem – unlike what the DuPont nay-sayers claim – I’ve *never* failed a compressor.

    And HC is generally cheaper too.

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