Discuss Mini Split AC

[Jim Andrew]

We get a "Country Living" magazine monthly from our local power company, and they have an article on mini split ac. It quotes that the seer on these are 28, which is a lot higher than the new central AC unit I had put in the house last year, think it is 16 which is the high efficiency unit. Have seen some discussion about these units for shops, but would like to learn more. Did a search and find lots of companies incl Amazon selling these online. If you have one would you please describe your experience?

[Robert Maloney]

We install a lot of them at work. You can either install one air handler or up to 5 on one condenser. We mostly install the Mitsubishi Slim units. They work very well in situations where you can't install central AC. We haven't had any call backs, so it seems they do a great job and the customers are satisfied. If you can't pipe the drain directly outside or down to a floor drain you do have to install a condensate pump. I personally haven't seen any units with a seer rating of 28, but I have seen them with an 18 seer rating. Of course the higher the seer the more efficient. With the higher efficiency comes a higher price tag, so you have to weigh out your options.

[Mike Holbrook]

The wife bought one on line to install in a room we keep boarding & day care dogs in. So far it has been nothing but trouble. Since we did not get it from a dealer, dealers wanted an arm & leg to install it. We payed almost as much to get the thing installed as we paid for it, contrary to what we were told. Once in it has been even more trouble. Basically it just does not cool properly. The latest theory is that there is not enough coolant for the length of the supply line. We have had the dealer work on it several times. Our installer/repair guys are telling us that these machines are very picky about exactly how much coolant they have. About 6 months after installing ours it is serving only as a fan, waiting for a service guy to show up again. They are suppose to try testing for coolant levels and leaks, which I believe they did at least once already. The supply line froze up last week so we had to turn the cooling off....

If it does not get fixed properly soon, I will cut a hole in the wall, put in a PTAC unit and be done with it. I have used PTACs, 3 of them, for 6-7 years, only needing to clean them and they cool well. I can install a PTAC myself, all I need is 230 outlet. Anyone want a deal on a mini-split?

[Keith Outten]

Jim,

I had a Mitsubishi split system installed in my shop two weeks ago today that has a seer rating of 19.4

So far the unit has been excellent, my shop is cool from end to end and the slow rpm fans both inside and outside are whisper quiet. I'm told the unit will produce 95 degree heat in zero degree temperatures so winter should not be a problem. The unit is compact, mounts high on the wall inside and the outside unit is installed parallel to the building so the small footprint of the system is nice feature.

We have had temperatures from 85 to 95 degrees the last couple of weeks, my shop temp is set on 74 degrees and it stays there constantly. So far I am happy as a clam.

I should add that my friend installed the system for me. He is a certified Mitsubishi installer and he has his Masters license in plumbing, electrical and HVAC so he is a professional.
.

[Matt Meiser]

My parents put in a 6-headed Mitsubishi Mr. Slim system last fall as part of a large remodel. Nothing but trouble but its 100% the installers' fault. 1/2 the units didn't work the first warm day this spring. 1 has dumped water in an upstairs room several times. A couple units have aulted more than once and the installer just resets the and tells my dad that should fix it. My dad told the GC, who I'm guessing will agree, that its time to tell the HVAC company they are paying for an independent inspection of the system. Point being that I think finding a reputable installer is critical. The comment this spring was that this is the first time they've installed a multi-unit system--should have mentioned that last fall.

When the system is working, its working well for them. The outdoor unit is compact and whisper-quiet--and theirs is a big one that I believe can support 8 indoor units. Indoor units are too obtrusive (mostly mounted on upper walls but 1 "floor standing" unit. Probably the biggest drawback I see is the lack of central control--you have to go around and shut off or change each individually with a remote control that's tied to each room. Not that big a deal, but it rules out modern smart thermostats.

I was told all modern HVAC systems are very sensitive to refrigerant charge, more related to the refrigerants and pushing the envelope on efficiency.

[David Weaver]

I have a 21 seer mitsubishi split in an add-on room that couldn't easily be tied into my ductwork. The only thing I can say is the authorized installer in my territory wanted a mint. Mine is a heat pump and ac combination, I ended up just having an HVAC installer selected through my contractor, who charged less than a third of the install cost from the authorized installer (it was going to be over $4k for the mitsu certified installer for a 15k btu unit to be installed at their negotiated price (i.e., they started higher, i negotiated to that point), and there's not a lot to the install). It cost me about $2800 including equipment to get the same thing installed through the contractor after buying the unit and line set from a plumbing supply place (which was about the same as the online cost, but at least I had a place to take it back to if it wasn't right). I have a "vanilla" setup, easy where the interior exchanger is close to the unit and above it.

Only the smallest units have the super high 20s efficiency.

If you have a normal setup where the unit is below the interior exchanger, it should be pretty straightforward to get any HVAC guy to install a unit if you know someone who will do it. If you don't, don't be surprised to find that a lot of places will want a whole lot of money for 4 hours worth of install work.

Anyway, all I have to do is go look at my meter with the split system running at 15k btu and my 30 year old 24k btu A/C running and the speed difference on the meter is probably a factor of 4 or 5. The efficiency is definitely there, and like matt said, it can be run pretty close to noiseless.

[Joe Leigh]

The reason for the very high efficiencies is due to the compressors and condenser fan motors being inverter driven. These DC motors are speed regulated depending on the specific load at each air handle location. They also employ electronic expansion valves that can vary the unit capacity greatly increasing its efficiency.

As for the 4 hour installation, well, done properly and professionally, this is not a 4 hour job. Nor is it a job for the do it yourselfer. In addition, as noted here, the refrigerant charge is critical. That is why these units come precharged from the factory given a maximum piping length. In most cases this is 25'. The manufacturer provides the amount of additional refrigerant needed beyond this length, usually in ounces. This requires specialized tools and scales to insure proper unit operation.

[David Weaver]

Yeah, it's not a DIY job, especially if you go beyond the line length. I believe it took the HVAC guy and his helper 4 or 5 hours to do the install ( the last hour, they were playing with it I think to satisfy their curiosity because they generally install a different brand). There were no access issues with mine, it's on a pad (vs. wall mounted), the electrician had already run a 220 line and installed a box.

Reason I mentioned the manual was not for a DIY install, but because if you drop the kind of money a split system costs, you should at least pay attention to what's going on (make sure the breaker isn't over the max rating, make sure that if the line set is over 25 feet that the installer adds coolant per the instructions, etc). It doesn't hurt to understand how it's set up, either, even if you're never going to fish around in it, and the owner's instruction manual is pretty skimpy on details.

If I'd have had a harder install, I could understand it taking a lot longer.

I did get the hard sell and the "your guy isn't using licensed installers if they will install it for that", "it will be installed poorly and look ugly", all of that stuff, and I would've gone with the certified installers if they would've been even close, but they weren't. It was worth the cost difference to just go another way.

[Matt Meiser]

Sheesh...just came back from my parents where I heard that they had yet another condensate leak. Make sure you've got an installer who knows what the heck they are doing!

[Keith Outten]

I feel lucky that my install went so well with no operational issues so far. We mounted the interior unit on the back outside wall and the outside unit directly below it on a pad that I put together. All we had to do was drill a 4" hole through the wall and run the lines down to the unit which was an eight foot drop. The lines and the drain are all contained inside a PVC cover that looks like downspout. My shop is the type of application that these were designed for, one large room.

One of the reasons for the higher efficiency ratings for split systems is there is no ductwork.
.

[Jim Andrew]

I'm getting the idea that these units are not common enough for the hvac companies to be familiar with. Matt's folks experience would not be what I'm looking for.

[Matt Meiser]

Sad thing is they had another bid about $500 higher from a company we had a good experience with who had quite a bit of experience with these systems. Mom's wishing they'd spent it now.

[John Hays]

I had a Gree 15k BTU heat pump installed about a year ago by a general contractor guy I like. The unit was his recommendation, against the brand I suggested, since it required only 115v to run (I wouldn't have to give up one of my 220v breakers), had a 5 year warranty and he could get it locally.

I was skeptical at first, but it seems to be working great so far and heats/cools a 550 sqft. garage that has an odd floor plan. The only problem that sprang up was it suddenly stopped heating this past winter. Fortunately, it was just an installation flub which turned out to be a loose seal that needed tightening... he came out and fixed it for free. Other than that, I'm very happy with my purchase. In fact, my system cost 3k after all was said and done, but I would do it again in a heartbeat!

I also agree with the others who advised hiring an installer who knows what they're doing. I couldn't imagine taking on such a technical project myself or dealing with the nightmare Matt's parents are going through now.

As a side note (it may just be me), but it seems that the harsher the weather gets, the better the unit works. Today was 88 degrees with 90% humidity outside... my shop was 74 degrees with 50% humidity inside. :)

[Richard Shaefer]

we have an old house that we wanted to retrofit with central A/C, but the ductwork alone was over $10k. We decided to go with mini splits. At the time, it was cheaper and there were tax credits available for the smaller units, so we did 1 independant unit upstairs and 1 downstairs and they worked friggin awesome, are dead silent, and cost FAR less to run that the old window rattlers. Could I have gone with a single unit with multiple heads? yeah, but i'd have missed out on the tax credit and with both a toddler and a geriatric dog in the house, I like having the safety blanket of redundancy if one ever does go down on me. I've had whole-house central A/C units die on me before in the heat of summer, and I'm never doing that again. Getting an A/C guy make a timely service call in July is about as likely as getting pigs to fly without explosives.

Agree with everyone who said that the install is key. I shopped around a long time for the best systems (Fujitsu beats Mitsubishi by a long shot), and then shopped around for the best installer I could find with good references. These things are not DIY in my book. It took 2 guys a full day to install each unit in my house, and they've both worked flawlessly for over 6 years.

[David Weaver]

I'm getting the idea that these units are not common enough for the hvac companies to be familiar with. Matt's folks experience would not be what I'm looking for.

The local guys here get company training, at least that's the case for the fujitsu installers. I'd imagine the same is true for the mistubishi folks.

[Steve Milito]

Any reputable HVAC company knows how to install a mini-split.
I just had a detailed discussion with an HVAC tech last week about mini-splits vs conventional for my shop.
We'll see how the quote comes in. He said he would probably design a really simple duct layout for conventional to just dump air in the shop, and that the conventional may come out less expensive. We had an interesting discussion about the upsides and downsides to each system.

[David Weaver]

The dust issue...one thing to consider, and I'd defer to an HVAC installer here to mention which is worse. Does shop dust, even if there's not much, present a problem for the internal exchanger? There are filters in the mitsu exchanger, but they certainly don't strike me as the kind of thing that will love lots of dust.

[Steve Milito]

The dust issue...one thing to consider, and I'd defer to an HVAC installer here to mention which is worse. Does shop dust, even if there's not much, present a problem for the internal exchanger? There are filters in the mitsu exchanger, but they certainly don't strike me as the kind of thing that will love lots of dust.

That was part of the discussion. He said that he could get a really good filter for a conventional unit but you are stuck with a fairly mediocre filter with the mini-split. He said that you can really gum up a mini-split if you don't keep the filters clean.

[John Hays]

That was part of the discussion. He said that he could get a really good filter for a conventional unit but you are stuck with a fairly mediocre filter with the mini-split. He said that you can really gum up a mini-split if you don't keep the filters clean.

Very true. When the mini-split was put in, I was advised to always keep the filter clean. Ever since, I've been checking my filter religiously every month. However, I have noticed a slight build up of dust around the inner components (I've been doing a lot of sanding lately).

I need to contact my installer to see if shooting a few low pressure blasts inside with a compressor would harm the unit or not.

[Michael W. Clark]

The dust issue...one thing to consider, and I'd defer to an HVAC installer here to mention which is worse. Does shop dust, even if there's not much, present a problem for the internal exchanger? There are filters in the mitsu exchanger, but they certainly don't strike me as the kind of thing that will love lots of dust.

This is going to be an issue with any HVAC system installed in a dusty environment. They are not designed to handle this dust loading. If you use "good" filters, they plug, are expensive (relatively), and need to be changed often. If you use coarse filters (cheap relatively), then dust gets to the internals and can foul them resulting in lower performance. Not sure what the solution is other than good DC, locating the return in a cleaner area, and/or turning off the fan during notoriously dust operations.

Mike

[Jim German]

As for the 4 hour installation, well, done properly and professionally, this is not a 4 hour job. Nor is it a job for the do it yourselfer. In addition, as noted here, the refrigerant charge is critical. That is why these units come precharged from the factory given a maximum piping length. In most cases this is 25'. The manufacturer provides the amount of additional refrigerant needed beyond this length, usually in ounces. This requires specialized tools and scales to insure proper unit operation.

I wholeheartedly disagree, I recently installed a Mitsubishi 26 Seer unit myself in about 3 hours, plus an hour to run the electrical. They are very very easy to install, its basically plug and play assuming you have 25' refrigerant lines. Even if you need longer you'll just need to add some refrigerant, which does take some specialized equipment, but still isn't difficult.


I think the issue is that most of the HVAC guys don't have a clue what they are doing, and are to lazy to just read the simple instructions that come with the unit.

[Steve Milito]

I wholeheartedly disagree, I recently installed a Mitsubishi 26 Seer unit myself in about 3 hours, plus an hour to run the electrical. They are very very easy to install, its basically plug and play assuming you have 25' refrigerant lines. Even if you need longer you'll just need to add some refrigerant, which does take some specialized equipment, but still isn't difficult.



Where can you get refrigerant, I thought its sale was limited to certificated HVAC contractors.

[Jim German]

Where can you get refrigerant, I thought its sale was limited to certificated HVAC contractors.
From the EPA Site (http://www.epa.gov/ozone/title6/phaseout/technicians_contractors_faq.html): There is no restriction on the purchase of R-410A or R-134a. The units come pre-charged with enough refrigerant for a 25' line too so you don't even have to find a place to buy it, although its easy enough to find online. (http://www.refrigerantguys.com/category-s/48.htm)

[David Weaver]

You can get it on ebay. I don't think it's so much an issue of legality to buy some of the refrigerants as it is the issue of adding and recapturing.

[David Weaver]

From the EPA Site (http://www.epa.gov/ozone/title6/phaseout/technicians_contractors_faq.html): There is no restriction on the purchase of R-410A or R-134a. The units come pre-charged with enough refrigerant for a 25' line too so you don't even have to find a place to buy it, although its easy enough to find online. (http://www.refrigerantguys.com/category-s/48.htm)

Now that's confusing! No certification required to service 410a equipment, but clearly illegal to vent it. my system literally required 2 ounces of additional 410a, I didn't install it, though at the time when my contractor was screwing around, I was considering installing the entire system and getting a certified guy to hook the lines up and add coolant. Fortunately, I didn't have to go that far.

[bobby milam]

I wholeheartedly disagree, I recently installed a Mitsubishi 26 Seer unit myself in about 3 hours, plus an hour to run the electrical. They are very very easy to install, its basically plug and play assuming you have 25' refrigerant lines. Even if you need longer you'll just need to add some refrigerant, which does take some specialized equipment, but still isn't difficult.


I think the issue is that most of the HVAC guys don't have a clue what they are doing, and are to lazy to just read the simple instructions that come with the unit.


I started doing some research on these and found several videos showing the complete install. I was kind of wondering if I was missing something because they looked simple enough for a DIYer to do. I think that I am going to get one and install it in my garage for these hot summer days. It will be hanging on the back wall within a few feet of the breaker box so unless I missed something in the video I think that I could do it in a couple of hours.

It is going in a 3 car garage, what BTU would you guys recommend, for the ones that are using them?

[Joe Leigh]

The dust issue...one thing to consider, and I'd defer to an HVAC installer here to mention which is worse. Does shop dust, even if there's not much, present a problem for the internal exchanger? There are filters in the mitsu exchanger, but they certainly don't strike me as the kind of thing that will love lots of dust.

These units are NOT designed for commercial or shop applications. They use electrostatic air filters, no better than you would find on a common residential window unit. So no, a woodshop is not a friendly environment for a ductless mini split.
One of the most common mistakes installers make is in drilling the hole for the electric and line set to pass through the wall. This hole must be drilled on a downward angle from inside to outside. This angle is necessary because the condensate leaves by gravity. 9 out of 10 condensate leaks are caused by improper drilling of this hole.

[Jim Falsetti]

My shop is small - about 2,500 cubic feet. The Mitsubishi 24,000 BTU unit was installed one year ago and it has worked great both in the summer and the winter. Would buy one again. The delivered price for the 24,000 BTU unit was $2,135.95. The Unit is efficient, with an SEER of 19. The installation was about $500. Used a licensed HVAC installer and it was done in a few hours. For that price, I did not investigate installing it myself. The condensate drain line is tied into the roof gutter downspout, which drains into our (town-mandated) rain garden and then the town storm drain. A typical hot, humid summer day around here is in the 90's with what seems like 100% humidity. I set the unit to keep the shop in the mid-70s with a 40% humidity. You may be able to get a rebate from your local utility, but check your State requirements. In Connecticut, you need to have a home energy audit done first. Jim

[Jeff Holoboski]

We have a high SEER Fujitsu in our 20x25 family room addition which keeps the room very comfortable in summer and winter...The company that did the install told us to religiously keep the filters clean for optimum performance so I think one would have to do it more often in a shop setting...The system works very well and I would consider one in my shop but they are pricey...

[Steve Keathley]

I was going to put a mini split in my shop, but had one similar to this that we used on a sun porch at our previous house.
http://www.homedepot.com/p/LG-12-000-BTU-Portable-Air-Conditioner-with-Dehumidifier-Function-with-Remote-Control-in-Gray-74-4-Pints-Day-LP1213GXR/203656279

I didn't think it would do much in my uninsulated 20' x 20' shop (there is an insulated studio above the shop, but the shop walls aren't insulated). However $20 (outside vent and drain pipe) and 45 minutes later I had a working A/C. It will keep the shop in the upper 70s on a 105 degree day in central Texas.

It takes up a little floor space, but is a whole lot cheaper than a mini-split and gets the job done.

[Frank Trinkle]

I'm planning to install a Cassette mini-split in my 3-car, 1000 sf garage workshop later this year. This unit: http://www.appliancesconnection.com/lg-lc427hv-i309131.html
Ceiling mounted and drain to either the gutter system, or directly to the shop sink down spout.
Dust mitigation will be by both a ceiling mounted air filtration system (from JDS), and a 3HP DC cyclone unit. My sanding is all done with Festool sanders and CT Vac's, and occasionally by hand on top of a large Grizzly downdraft table. I am assuming that this will virtually eliminate the problems of gumming up the AC filters or damaging internal parts.

This unit is pretty highly rated especially for dehumidifying, which is rather important in Florida, and should protect my cast iron and wood.

I'd sure like to hear anyone's cautions on this, or other suggestions before I dump over $5K into the system and install. I think I've done my due diligence, but open to comments.

[John Stankus]

I just put in a Mitsubishi mini split in my shop (3 car garage (with 2cars)).

Install is not hard, just need to make sure on some details
1. Use Nylok on the flare connections. This is a polymerized compressor oil that helps prevent leaks in the connections
2. Make sure to properly evacuate the system. You need to use a good vacuum pump AND a vacuum gauge that reads into microns of vacuum (A pirani gauge or the like). Evacuate below 500 microns. It may take a while to pump out all he moisture. (Vapor pressure of ice is about 3 mm Hg)

R410a is available from the refrigerant guys. And other sources.

This has kept the temperature in the shop between 70 and 73F, and I am in San Antonio . Walls are not insulated (yet), but attic is. Shop has been quite pleasant so far this summer, which being a teacher the summer is when I have a little more free time


John

[Jim German]

I'm planning to install a Cassette mini-split in my 3-car, 1000 sf garage workshop later this year. This unit: http://www.appliancesconnection.com/lg-lc427hv-i309131.html

42,000 BTU's seems like an awful lot for that size shop. I would think something like 24,000 BTUs would be more appropriate. I also found that the ceiling mounted ones were significantly more expensive than the wall mounted ones. Keep in mind if you oversize it, it won't de-humidify as well as a properly sized unit (although these ones are all variable speed so it should still do a decent job).

[John Stankus]

42,000 BTU's seems like an awful lot for that size shop. I would think something like 24,000 BTUs would be more appropriate. I also found that the ceiling mounted ones were significantly more expensive than the wall mounted ones. Keep in mind if you oversize it, it won't de-humidify as well as a properly sized unit (although these ones are all variable speed so it should still do a decent job).

There are online sizing estimators to get the proper unit. Look for manual J calculations. Also insulation is your friend!

I put in a 12k or 14k btu unit. And it seems fine. This was sizing calculated with a manual j online estimator with wall and ceiling insulation. I only have the ceiling insulation installed, and it keeps up fine (we have hit 100f a couple times with fairly high humidty. When first started I was getting a pint of condensate every 4 or 5 minutes)

John

[Jim Andrew]

When I built my house 32 years ago, my thinking was that insulation was the cheapest material I could use to save money as time goes by, so built the house with 2x6 walls, blocked the overhang and installed vents to the attic from my soffits, put R 38 insulation in attic, caulked to seal around wiring to attic, and other little things, and have gotten by with a 2 ton AC unit in a 1736 sq foot house all these years. And last summer when it was 114 degrees outside, the ac kept the house below 80 degrees, without running constantly. So my thinking is Frank could get by with a smaller unit if his building is insulated well.

[Will Rowland]

Any reputable HVAC company knows how to install a mini-split.

Have to disagree...we went through absolute heck with 5 different "very reputable" AC companies in Houston trying to get a 2-zone mini-split to work properly. Mini-splits are still foreign to most AC guys, and as a result they try to apply a "conventional" AC thought process to mini-splits. Eventually I had to do the research and call the mfr myself, and then get an AC guy out there that I basically instructed on how to "fix" the system (it works great now).

Here's the most important thing I learned - the only time you should EVER use a set of refrigerant gauges on a mini-split is if you are pressure testing the line set with nitrogen. Refrigerant should only ever be added/removed/checked by weight, not pressure. Single zone systems under 25 ft are generally OK with the pre-charge, but multi-zone units absolutely must have the refrigerant weighed in, based on the combined length of the line sets.

In other words, if an AC guy comes to check your mini-split, and pulls out a set of gauges, tell him to leave immediately. Also, the system should be evacuated initially using a micron gauge to check the vacuum, not a conventional dial gauge that only reads to -30".

[Joe Jensen]

I have a 28,000 BTU Sanyo mini split in my shop. Had it installed maybe 4 years ago and I've had no problems. I have an excellent AC guy, he's a engineer who decided he liked AC work better than engineering. I did build a box around the air inlet to hold larger filters. There is no way I'd run it without the extra filtration. The installation seemed very straight forward. The installer and I are both engineers so we both read the manual. I helped and I think we still spent 5 or 6 hrs. I'm pretty sure the instructions for my unit were very specific about the refrigerant instructions like what Will Rowland said above. I wanted the most BTUs I could get on a 20A 220V line (limitations of the shop) and I think the SEER on mine is like 28. Mine works well if you keep the shop cool but if you start it when it's hot (like 105 or more here in Phx) will take all day to really cool down. For example, it's 108 today Friday afternoon here in Phx. I want to work in the shop Sat. The shop is 91 inside right now. If I started it now, it might cool down to 85 or so in 6 hrs. I will instead start it when I go to bed and it will be 76 in there in the morning (91 outside at the coolest). It cools MUCH more effectively when it's below 100 outside. Also, these units all cool less and less efficiently the hotter it gets outside. All have a max spec around 110-114. I would guess mine only cools maybe 10-20% of what it would when hotter. This is computer controlled and while it cools a lot less, it also draws less power. Once the shop is cool, mine usually only pulls 6-7 amps. I'd guess that once cool the shop would cost less $5 a day to keep cool here in Phx. But initial cooling here in hot Phx would draw 20A of 220V for say 12 hrs would cost $.57 per hr or $6.84, and then $.18 per hr after. My shop has a well insulated ceiling and rear wall. I also have R17 garage doors. The side walls are not insulated other than 1" of crappy foam under the stucco and then drywall...joe

[Mike Holbrook]

Thought i would post an update to my mini split situation. I gave up on the original company that was trying to get mine working. In retrospect I think they used a subcontractor to install the unit because they lacked the knowledge. I have a new company now and they have mine working. Apparently "charging" these units is tricky. If the job is not done exactly right they do not work correctly. My new guys located and bought an adapter for their charging unit. I was told that different manufacturers use different adapters and the installer has to have the correct one. The guy told me he only added a couple ozs. to our unit. Whatever he did it is working great now. It may have been more an issue of having the right equipment.

I think it is important to have a company install these units who has experience with them. It took me three tries but I finally found someone who did. My new guys like the Mitsubishi units too. If I had it to do over I would buy a Mitsubishi.

[Phil Thien]

In other words, if an AC guy comes to check your mini-split, and pulls out a set of gauges, tell him to leave immediately. Also, the system should be evacuated initially using a micron gauge to check the vacuum, not a conventional dial gauge that only reads to -30".

Well then how are they supposed to check the amount of refrigerant in the unit without completely evacuating the unit and weighing the canister?

There has to be more to the story than this.

[John Lanciani]

Well then how are they supposed to check the amount of refrigerant in the unit without completely evacuating the unit and weighing the canister?

There has to be more to the story than this.

My HVAC guy told me the same thing after installing three Mitsubishi units for me. He said that the wiggle room in the charge is so small that if gauges are regularly used the charge will be too low after just a few measurements. Instead my guy measures the temperatures of the lines to determine if the systems are running properly and only uses gauges if the line temps are not as expected or if the units are not functioning satisfactorily.

[Todd Mason-Darnell]

My HVAC guy told me the same thing after installing three Mitsubishi units for me. He said that the wiggle room in the charge is so small that if gauges are regularly used the charge will be too low after just a few measurements. Instead my guy measures the temperatures of the lines to determine if the systems are running properly and only uses gauges if the line temps are not as expected or if the units are not functioning satisfactorily.

I have a Mitsubishi Mini Split as well. MY AC guy used to do commercial installations, before he went into business for himself. He has told me the same thing. Mitsubishi does not recommend checking the pressure level because of refrigerant loss.

[Joe Leigh]

Well then how are they supposed to check the amount of refrigerant in the unit without completely evacuating the unit and weighing the canister?

There has to be more to the story than this.

Of course there is. Most of these posts are coming from guys who are not in the field and are just repeating what they heard or what their buddy said.

You most definitely CAN connect a gauge manifold to an operating 410A system and once again this is NOT a DIY job. Unless you are trained to know to know and recognize the correct operating pressures for a given set of operating conditions, you need to leave this to a professional.

These R410A inverter driven systems with their electronic expansion valves have a very critical refrigerant charge. Special equipment is needed to properly charge these systems as a difference of even a few ounces can affect system performance. This is not a job for a homeowner regardless of what is posted here.

[Leo Graywacz]

I was looking at mini split ductless systems for my 1300 sq ft shop and There really wasn't a good spot to put the inside unit without making it far away from where I'd liked it to be.

I'm amazed at how small your systems are for cooling the spaces you have. You must have really good amounts of insulation and low ceilings.

A little off topic because I went conventional

I put a 4 ton (47,000BTU) Rheem 16 SEER split system in my shop. Did everything myself except the connection of the copper between the condenser and air handler.

For you guys with larger shops (1200+) what are the CFM ratings on the fan for the system?

My shop at 1300 sq ft isn't that large until you look up. I have a 26' peak for my ceiling. I average it out at about 24'. My shop is 33,000 cu ft so I needed a good fan to make sure I could move some air.

I mounted the air handler at 8' so the outlet is about 9' up. After the HVAC guy got it installed it was about 11am and the shop was 86F. By 5pm it was down to just above 70F. It was chilly.

Now when I come to the shop it's usually about 83F. I turn it on and in less than 2 hours it is at 76F which is where I keep it. It's nice. My shop regularly got up to 92F every day on a normal summer day.

As for filters I made sure that I have a good filtration system. And because I know it'll be dusty at times I wanted to be sure I had enough filter area to make sure I could keep a good airflow going if the filters started to get clogged. I have 5 filters in it, just cheap FRP 4, MRV 8s. I don't care about bacteria and smoke particles. Just good enough to keep wood flour dust off the coils.

Can't believe no pics in this thread.

http://www.fototime.com/780DD5CF9610E6B/orig.jpg

http://www.fototime.com/F7949D1B8BFB3EC/standard.jpg

http://www.fototime.com/EF70C0615495FFC/orig.jpg

http://www.fototime.com/4D93E9684908213/orig.jpg

[Jim Neeley]

Leo,

With that size of a shop and such high ceilings I'd take a look at something like the Basic 6 ceiling fan by Big Ass Fans (Google it). I'm thinking you want to move a large volume of air but don't need to pay the electricity for hurricane-like speeds you'd get from short blades. Their fans are only about 100 rpm but range from 12' to 24' in diameter.

Jim

[Leo Graywacz]

The last thing I really want to do is to try to mix the air up near the ceiling with the air near the ground. The cool air sinks and displaces the warm air. If I mix the whole room then I'll likely need a bigger unit. The 4 tons I have are a little shy of being able to do the job properly. If I had no sun gain from the roof then it would be more than fine. But between 11 and 3 the sun really heats the roof up and it radiates into the room. This is what killed me when I didn't have a cooling system. My bay would normally get beyond 90F even if it was cooler outside.

I designed the system to try to keep the air near the floor cool and I really don't care what the air above 6' is.

[Jim German]

You must have really good amounts of insulation and low ceilings.

Good amounts of insulation is key. Much, much cheaper to have a well insulated and well sealed shop than to try and cool and leaky shop.

[Leo Graywacz]

This isn't my building. I've already put in AC. I'm betting insulating this place would cost just as much as the AC did.

[Tom Rossman]

I am renovating my shop which has two rooms of 350 Sq ft each. I bought a no name Chinese mini split two years ago on line on sale for a little over $1000. I installed it myself except for the final copper hook up which a local HVAC guy hooked up and tested for $100. it works fine. Last year I bought a better quality LG unit for the other room for about the same price and did the same drill except I was able to trade a tool box I don't use for the copper hook up. The LG unit seems more efficient even though they are both 20 SEER units.

You do need to keep the filters clean, so I have a plastic tube gizmo that hooks up to my shop vac that I use to suction dust out of the screens. Seems to work fine so far.

best time to buy is in late Summer or late Spring when heating and cooling is not needed much, so a lot of units go on sale.