GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

MR. COOL or others DIY HVAC

ronny2b | Posted in General Questions on

Has anyone recently done a DIY installation using MR Cool or other DIY products that have pre-charged line sets?


I am rehabbing a house that is very rural.    This house never had any central heat or AC.     I have completely reframed the interior of the house and have planned for a high efficiency heat pump.     I had a few quotes on having someone install and due to location and current conditions the costs are astronomical.     I am not worried about doing the ducting, did a comprehensive manual J, but concerned about getting the lineset right.


Any experience here?






GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. gusfhb | | #1

    I have self installed 7 heat pumps. I suggest buying the best brand that fits your budget and finding a tech that will do the vac/pressure test on the system.
    IMO the rates charged to install a 1 ton heat pump are borderline criminal.
    Worried about warranty?
    Buy two units and store one. Cheaper than paying for install.

    Almost 50 unit/years of self installed mini splits.
    One failure
    On a budget unit.
    Less than 500 bucks to the AC man.

    1. ronny2b | | #2

      The challenge is finding someone to d0 the vac/pressure test. Why I was asking about Mr. Cool since they have pre-charged linesets.

      I am still looking for that tech. That would be my preferred route.

  2. gusfhb | | #3

    craigslist fb somewhere
    mine was a friend of a friend
    worst case call for a service call and negotiate with the tech that arrives
    My guy always re flared the ends
    otherwise it is no different than any other service call

  3. Tim_O | | #4

    I have DIY'd a few AC systems. One Mini Split and two vehicle AC systems in engine swapped cars where I made my own fittings on my lathe and all.

    The mini split is in my garage, I bought a Senville off eBay. Been working great for a number of years. It comes precharged, but you do have to vacuum the line sets. I'm not sure you even have to do that on the Mr Cool.

    What I do for my AC systems - I bought a set of gauges, and I rent/borrow a vacuum pump from AutoZone. I connect it up, let the pump run for 30 minutes or more, to ensure all moisture is evaporated and evacuated. After that, I close the valves and check in an hour to ensure that it has lost no vacuum. I think on my last car, I left it overnight. For adding refrigerant, I just weighed the cans of R134a as they went in on the car. Mini Split was already charged with the correct amount.

  4. walta100 | | #5

    Have you consider the “Mr. COOL DIY” units?

    There are no braze, solder, flare fitting the pre charged lines simply screw together with their patented fittings. No special tools. No vacuum pumps. No gages required.

    The only down side is you can’t shorten the length of the copper tube. You must make a loop or move the unit to use any extra.

    I have install one it work perfectly except for the water from drain hose I damaged.


    1. Expert Member
      DCcontrarian | | #6

      None of the previous four responders seem to have noticed either, but the subject of the post is "MR. COOL or others DIY HVAC."

      1. Tim_O | | #7

        I think all of us did, just Walta missed that. That's why I mentioned my DIY stories and how I handled the vacuum portion if not doing Mr Cool. Mr Cool is the only one on the market, as far as I know, that requires no vacuuming of the line sets. A good number out there are pre-charged, I don't believe that is the case with the big name ones though (Mitsubishi, Fujitsu, etc).

  5. walta100 | | #8

    Tim_O MR COOL is the only legal option for a DIY install for a split system I know of if we define DIY as someone without an EPA licensed.

    As I recall any work that may lead to a release of refrigerant like brazing, soldering and connecting flare fittings all operations that could leak and require a license.

    At present the EPA does not seem interested in enforcing the refrigerant rules. For the longest time the EPA ignored the people deleting equipment from diesel trucks and someone flip a switch and the EPA started sending out huge fines. Don’t wake the sleeping giant.


    1. Tim_O | | #9

      This is true, I believe others here have mentioned the license is fairly easy to obtain though. Might be worth considering if going to route of another mini split other than Mr. Cool.

  6. Jeremiah_Sommer | | #10

    I installed a 12kbtu Mr Cool system last summer and it was very straightforward. I was fortunate to have a route for my line set that allowed me to store the excess in a safe and out of site location. The system works very well and was an easy DIY project. Long term durability will be the test I suppose but after one full year of using for both heating and cooling, so far so good.

  7. gusfhb | | #11

    At no point in a standard mini split install, do you need to handle R410. It is of no more risk than a MR Cool.
    Take the online test if you wish, not sure a slip of paper will teach you how to flare copper lines.

    I am confident the OP will with some effort find a tech to do the refrigerant work without having to pay exorbitant install costs.

    Not supposed to install a toilet yourself here.....

    In a world where they sell R134 DIY kits on the shelf at every auto parts store in the country, I think we can be realistic about the risks involved in a mini split install.

    My operating assumption is that the MR Cool are of lower quality than a Mitsubishi, but that may be a flawed assumption.

    Most of a mini split install is carpentry
    The refrigerant handling skills are just not important to know for the average homeowner who will do this once, so the effort to find a pro who will be amenable is worth it.

    BTW the hardest part is getting the drain right
    If a pump is potentially in the mix, do it.

    1. aunsafe2015 | | #12

      "At no point in a standard mini split install, do you need to handle R410. It is of no more risk than a MR Cool.
      Take the online test if you wish, not sure a slip of paper will teach you how to flare copper lines."

      Releasing the refrigerant from the linesets after you have flared and attached the lineset is enough to trigger EPA 608 requirements. In fact, relevant guidance on the issue explicitly says that any split system requires an EPA 608 certification.

      As mentioned, this isn't really enforced these days. But do not be deceived: If you want to be certain you are compliant with federal regulations, you should absolutely be EPA 608 core and type 2 certified if you want to install a mini split (unless you are having somebody else who IS certified do the lineset/refrigeration release aspect of the install).

      Nobody is saying that the certification is what teaches you how to do the job.

      Edit to clarify: I meant opening the valve to "release" the refrigerant from the compressor into the lines/evaporator. Not "release" to the atmosphere. As explained below there would never be any reason to do that during a mini split install. And except for certain de minimis type releases, purposefully releasing refrigerant is illegal, as studying for the EPA 608 cert would teach you.

      1. Deleted | | #16


  8. gusfhb | | #13

    >>Releasing the refrigerant from the linesets after you have flared and attached the lineset is enough to trigger EPA 608 requirements.<<

    Why would you do that?

    Properly done, there is precisely zero reason to release any R410 in the install of a mini split.
    It is my feeling that a cheap mini split is more likely to release its refrigerant to the atmosphere now or later than a first line brand, but, again, I could be making an invalid assumption about MrCool.

    1. ohioandy | | #15

      Gustfhb and everyone, let's be precise with our terms. Nobody's purposefully releasing any refrigerant. Aunsafe means opening the valve to allow refrigerant into the lineset. Aunsafe is correct that EPA Section 608 requires certification whenever refrigerant is handled. The law is very clear about what constitutes "handling." Opening a valve that allows refrigerant to pass into a lineset, plus basically anything that involves installation, repair, or decommissioning of the pressurized loop is subject to 608. Presumably, Mr. Cool thinks they've found a grey area, but it doesn't seem grey to me. Mr. Cool units do not benefit from a system vacuum and nitrogen pressure test, which is the only responsible and prudent way to commission any refrigerant system.

      The certification is NOT that easy--you really need a good grasp on the principles. And like many government regulations, it may at first seem burdensome and silly but a thoughtful person, taking the time to understand the science in light of the cavalier attitude taken by many pro's and DIY'ers alike, may come to see the wisdom in it.

    2. aunsafe2015 | | #22

      "Nobody's purposefully releasing any refrigerant. Aunsafe means opening the valve to allow refrigerant into the lineset."

      Yes, exactly what ohioandy said. Obviously with a mini split install you are affirmatively not supposed to release any refrigerant -- they are precisely charged. If your lineset is long enough, you might have to ADD some refrigerant -- but never release.

      I meant opening the valve to release the refrigerant from the compressor into the lines/evaporator. Not "release" to the atmosphere.

  9. walta100 | | #14

    The test has nothing to do with completing the work. The point of the test is to prove that you know the rules about not releasing refringent into the atmosphere. If they catch you illegally vent you can’t say you did not know and understand the rules.

    Doing this work without a license puts a huge target on your back, in fact the EPA is paying a 10% bounty of any fine collected should you report someone. The fine start at 25K.

    The EPA has decided that making the connections in the way you described is handling refrigerant and requires a license. Arguing with the EPA seems like a losing battle but be my guest.

    If you did this work without a license, you would be a fool to brag about that fact on the internet.

    If I am not mistaken Mr. Cools equipment is manufactured by second largest producer of refrigeration equipment in the world. I don’t think the low price has to do with the quality of the product it has more to do with cutting out 300- 500% in markups from distributors, wholesalers and installers.


  10. idahobuild | | #17

    Is it the case that the Mitsubishi heat pumps, line sets and wall units from say HVACDIRECT.COM don't include refrigerant. If that is the case, then most of the work is, as stated earlier, mostly carpentry skills -- aside from any potential EPA violations . :-)

    1. ohioandy | | #18

      Mitsubishi outdoor units come pre-charged with R410A from the factory with the proper amount of refrigerant for a 25' lineset. The indoor unit is packaged with a charge of nitrogen to ensure it's leak-free when you get it. Linesets are full of air and moisture and maybe a bug or two. For simple installs, if you buy ONLY a vacuum pump/guage, a couple fittings and hoses and some nitrogen, study up online and get yourself the Section 608 core and Type II, then you're good to go on a fully legal self-install. For minisplits you don't need the standard AC hi/lo gauge set of yesteryear. Oh, and you don't even need to be good at flaring any more--you can now get Sharkbite-type push connectors for refrigerant lines.

      1. aunsafe2015 | | #21

        "Oh, and you don't even need to be good at flaring any more--you can now get Sharkbite-type push connectors for refrigerant lines."

        Andy, any idea how well these things works? Are you aware of a specific product that has a good reputation?

  11. matthew25 | | #19

    It looks like you only need a 72% to pass the exam. 18 out of the 25 questions in each section. I was curious how hard the questions were, I got 5 out of the 8 free sample questions in the Type II section correct on this below site so I’m sitting at 63%. Would not be hard to pass I think. I also read there is an open-book version of the test but you’ll need an 84% to pass.

  12. brian_wiley | | #20

    Hi Ron, I’ve done a MR COOL Universal Heat Pump install with a DIY pre-charged lineset like you’re considering, and for the same reason, too. The cost was just something that circumstances at the time couldn’t bear.

    I outlined the install and considerations in another thread on here, but the gist is that I’m happy. I re-did duct work with mine, and the total cost was around $4k for a 24k btu unit. It works great here in zone 5 in a house with around 9.5 ACH, and without backup heat as well.

    That said, I now know quite a bit more about HVAC (due to some adjacent work I do at my job), and might consider installing a more mainstream unit after getting EPA certified. The primary reason for that is serviceability. I knew going in that it would be difficult to find service, but because we don’t have a Gree dealer in the state (the Universal is a rebranded Gree) it’s impossible to get someone to look at it when that time comes. Additionally, it is single stage, and a modulating/communicating unit would be nice. The Universal does some algorithmic-based modulating, but it’s very primitive compared to a VRF unit.

    Like I said, I’m happy, and think you would be too. It’s a fairly straight forward install. If you decide to that route feel free to email me at brian.maxwell.wiley [at] gmail [dot] com and I can point you towards some Gree install documentation that was really helpful.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |