In this two-part series, craig migliaccio from ac service tech came down to our apprentice school at lake technical college in eustis florida and did a couple different classes. This is a two-part series on ductless mini split systems and in this first version we're going to talk through the air conditioning mode on ductless systems. So we've got two slides. This is in the air conditioning mode.

Then we have in heating mode. Does anybody know why uh both the large line and the small line have insulation over top of them on a mini split the heat surrounding it when it's traveling through the building? What's the other reason, what is it so in this case, you have uh both low pressure lines uh and that's because the metering device is outside yes and and how does that end up affecting if you didn't, if you didn't have insulation and the line set was Traveling through the inside of the building, what would happen you wouldn't know the right amount of superheat that you have because you're absorbing all that much heat from the outside? What were you going to say? Okay, so what's going to also happen, yes, that those things are definitely going to occur, but the the probably the biggest thing to the building is thank you yep ruining the building. Yes, absolutely yep both are going to be low in temperature and it's going to attract humidity. It's going to condense on the tubing and it's going to drip down messing up the building, yep good.

So that's different than a regular air conditioning system, because the metering device in the standard air conditioning system is going to be at the uh, the indoor head unit and i'm sorry in a regular air conditioning system. The thermostatic expansion valve is going to be right at the inlet of the evaporator coil. In this case, we have a mini split system, so we have an eev electric expansion valve at the outdoor unit and it has a stepper motor and it's able to very, very precisely uh, be able to bring up and down that rod in the center. And so you have a permanent magnet in the center and you have your your your wire coils.

It looks like it's two, but you have multiple different wires and you and it's it's just stepping stepping and turning turning this needle up and down on the inside of there so kind of hard to see. But right here you have your reversing valve and uh. So so right now we're in air conditioning mode. So this is all low in temperature, because you're the refrigerants, absorbing heat from the inside of the building out here, you're rejecting heat to the outdoor air so step one is the compressor inlet.

So you have your low pressure, low temperature vapor refrigerant entering into the compressor. Does anybody know what the accumulator, what the accumulator's job is? Does anybody know that what do you got? Yes, keep the compressor from slugging, so it's it's safe, guarding the compressor making sure only vapor enters the compressor good uh. What what else does the accumulator do? Stores stores refrigerant right, so a mini split. A lot of times is a vrf compressor and it may only be uh it's not using as much refrigerant when you have a lower heat load in the building.

If you're trying to drop the temperature quickly with a mini split, you can ramp that compressor all the way up using your remote in order to reduce the humidity and temperature inside the building quickly and so, depending on how much refrigerant is being used. Like we said before, a metering device such as a thermostatic expansion valve - or in this case it's the eev with multiple temp centers monitoring, the super heat, the sub coiling and line temperatures. It's able to efficiently create a saturated state in here, and it can even a lot of times. It runs in a saturated state that may be say six or eight degrees.

In fact, you may even find that the total superheat on a running uh mini split system may be zero, zero degrees of superheat and the reason is they have the accumulator on them to protect the compressor and they're, making the the the best use of the space Within the the coil at the indoor unit, so you might find anywhere from say, zero to five degrees. Even you know of total superheat. If you were to measure right here now, a lot of the manufacturers don't want us to check sub cooling and super heat, and that's a lot of times why they don't put a another pressure port right here. They don't want to confuse you compared to a single or two speed standard split system.

You just have your your your mini split here that can ramp up or down, depending on the heat load, so good. Now you're gon na have either a two pipe or a single pipe. Every time you have a rotary compressor like this. Your rotary compressors are all popular on the on the outdoor mini split units, you're, going to always have an accumulator mounted to the side.

You may have just one or you might have a second one as well. You may have one before this one and that one is acting more of a more as a storage vessel for the refrigerator, and this one is more so safeguarding the compressor so inside the accumulator. You have these little holes at the bottom, where it's sucking in the oil and and liquid refrigerant, but it's really trying to get the oil and bring it in because you'll just have oil gather up in this whole thing, but it sucks it in and any liquid Refrigerant phase changes it because of the small little orifice the little hole into the vapor line and then goes into the compressor to lubricate. The parts in here so sometimes you'll have a screen up here to help vaporize it as well up at the top depends on the accumulator style, so you can have one or two accumulators in a mini split.

Sometimes these are called ductless. I think i think you call them duckless a lot right: brian yeah, yeah, ductless and then uh you can call them ductless mini split. I that's why i put both words up here at the top, so you got your low pressure refrigerant entering the compressor. Then you have your high pressure, high temperature vapor refrigerant exiting, and then you have your discharge line.

It's going into the single side of the reversing valve. So then it enters the reversing valve and and there's there's. Let me see here: yep, there's the up close, we'll get to that in a second, but basically you have your discharge, gas, traveling across the side and then over to the outdoor coil during air conditioning mode. So here's the up close of the reversing valve here you have your solenoid valve over here here you have a pilot valve and you have four little tubes that are attached there and so what's happening.

Is this little tiny pilot tube? It is - and i like how you just referred to that in your in your last video, but but that is a little mini, reversing valve. Basically, so, basically, what you're doing is based on the the solenoid valve position. What you're doing is you're applying pressure to one side of the reversing valve and you're pushing the slide over and you're connecting these two over here and there's a little teflon seal and it just rides across there. It's loose on the inside of this reversing valve this high pressure.

That's surrounding it is pushing down on it and there's a brass plate on the inside, and so it slides back and forth, but it can slide easily just bait it. Just it's just sealing it. Based on the pressure above it, but anyway you have high pressure entering this side. You have low pressure over here, so the high pressure is able to push it across if the refrigerant charge is too low, then that reversing valve's not going to operate correctly.

It's not going to shift over, but in this case it's it's traveling on the outside and during heating mode. It will come across over here and this slide will be over here. So wherever the slide is that's your low pressure, so you have your vapor desuper heating. So super heat is the temperature increase above the state above the uh saturated temperature.

So basically you know if you're all the way up at say a 170 degrees or something like that: you're rejecting heat and lowering in temperature as a vapor and that's called d superheating. All these fancy words that we use that you know you just kind of want to know it's just lowering in temperature as a vapor refrigerant, and then it enters a saturated state once again and where liquid and vapor both exist. You have your saturated state where it's. It's locked at a certain temperature rate as it enters where vapor liquid exists until it comes out and a good temperature to say be, maybe 100 degrees and then, where it comes out, it may be 90 degrees.

And so that's your your 10 degrees of sub cooling. So anyway, it comes out, say: 100 degrees, the temperature uh, the lowering of the liquid refrigerant temperature between here and here, that is your sub cooling. If it's a single zone unit a lot of times, there's no access port to be measuring the liquid line pressure. So you you don't have access to that.

However, you could potentially place temp probes in in spots to take a sub coin reading, but they want you to stay away from that and they want you to just on many split systems to if you think that it's low on refrigerant to recover all the refrigerant Check for leaks fix the leaks pressure test. It then vacuum pump. It then weigh in the correct amount of refrigerant based on the rating plate on the outdoor unit, plus any additional fee past what the unit comes with as far as the refrigerant. So if this is, if it comes with enough refrigerant for 50 feet - and you have 65 feet from from the outdoor unit to the indoor head unit, then you have to add that additional 15 foot worth of refrigerant into the system when you break the vacuum, with A liquid refrigerant from the bottle, the other nice thing about it is it has an accumulator.

So if you only have one port, you know you usually break the vacuum with liquid refrigerant into the liquid side. In this case, you know you may only be stuck with the vapor side. You may not be able to weigh in the full amount, because this is bigger - a bigger tube than this, but you're going to get all of that liquid refrigerant into that system. That you know needs to happen, even if it has to happen while the system's running, you can also increase the temperature on your bottle.

So if this is off, you can increase the temperature of the bottle to push more refrigerant into the system. That's a good way of doing it to try to get the correct amount of refrigerant before you turn the unit on. Does anybody have any questions? Yet that's especially important when it's uh low ambient temperatures you can use like a heating blanket or something like that? Do that safely, don't go putting a torch on your tank, yes, yep yeah. They just make a plug-in heater that you strap around.

The tank increases the temperature, which increases pressure, which then you can measure it with your scale. You just kind of have to tear the tear the scale out with the heating blanket on it, and you can see how much additional refrigerant you're getting into that system. So that's how you would do that if the system is off so sub cooled liquid enters the eev. Here's up close of the eev.

This pathway right here is a little bit more elongated and has like different sections of different cones. The the variance or the the the the small area is very, very precise on these eev systems. So you have your stepper motor right here and you're. Just it's just turning this and if you were to ever recover refrigerant out of a mini split unit and you turn the the power off to the system, you can pull the head off and you can take a permanent, magnet and and turn it counterclockwise.

So this this section is all the way up: you're not going to be able to over extend it. You know upwards, it's going to be it's going to just kind of ride at the top of the thread. So when it turns back on again, the motor is going to going to kind of reset itself and it's going to get back onto the threads again. So that's a way to open up this pathway for for recovery is to take that turn the power off.

Take the head off permanent, magnet counterclockwise. It opens up the pathway for you any questions on that. It's good stuff right there, that's actually good! That's really good knowledge! Oh here's an up-close view of the uh. Well, it's just a little tiny hole.

These are like little metering devices, but really all it's like a little. It's like taking an awl on the side of a pipe and there's a pink like that, and it makes a tiny little hole. That's really all this is here and here it's trying to suck the oil that gets stuck in the bottom of this tank back into the vapor line. So it goes into the compressor.

So you don't just fill this up with with uh refrigerant oil instead of liquid refrigerant, and you got ta remember that liquid uh i'm sorry. Oil goes through the entire system with the refrigerant. So it's important that the refrigerant is traveling at the right velocity. It's it's! It's miscible with the the oils miscible with the refrigerant and the refrigerants, carrying the oil throughout the whole system.

So it's important to use the right refrigerant oil that mixes with that refrigerant that you have in the system and that's why you see the different alternative refrigerants retrofit refrigerants for r22 they're, really, the reason they have six refrigerants in in them to try to maybe get To the right mixture is they're trying to grab a hold of the oil as it as it as the refrigerant travels through the system. That's the hard part about the retrofit refrigerants. That's why they add, say a semi-flammable refrigerant, you know, or partially flammable refrigerant in that mix, but when you add it in the mix, the refrigerant is not labeled as flammable because of the mixture. Anyway, right here you see the refrigerant, even though it's it has to travel all the way to the evaporator coil.

It's going to be less vapor than normal because of the size of the tube, but you're still going to have some little bit of vaporization. That's going to occur in in the small little quarter, inch tube - if this is this tube - maybe 3 8 of an inch and that's 3 8 od, which is outside diameter. It's also referred to as acr. It's also referred to as soft copper, but, but basically this is this is usually a quarter inch and this is usually three eighths, but this could also be um, 5, 16 or another size to try to increase the capacity for especially during heating mode all right.

So you have your liquid refrigerator your low pressure, low temperature, liquid refrigerant after x of the meter exits. The metering device goes through the two position: surface valve uh and uh, and and through or three position. It's going through your surface valve and traveling to your indoor unit, and so we kind of have this blanked off right here, because you don't know how it's traveling it's hard to get both of these items on the same picture. So that's why there's a little kind of gap, but this could be traveling 20, 30 foot horizontally whatever before it gets to that indoor head unit.

So you have your liquid enters the indoor coil. It comes right into the side right here, and it immediately is in the saturated phase, change that's occurring and, like i said before, the mini splits can operate with an extremely low total superheat, and that gives it the ability. Have you guys ever noticed that the the delta t on mini splits can be higher than a standard system? Has anybody noticed that that's because of the they use a better availability of the space in the evaporator coil, the super heat is lower, and so it can safeguard the compressor and run with a lower superheat, and it just depends on what uh fan speed you're running It at if it's automatically controlled or you're overriding it with the with the air speed with the remote, but that's also why they don't want. You necessarily checking total super heat and sub coin.

But i will tell you that if you check this and you're noticing an extremely high superheat or total superheat out here, that's an indication that you have low refrigerant charge. So, though, you can't really check the refrigerant charge by using the ports depending on the unit and usually they don't give you a guide to check the charge. You know, i don't know you know if you, depending on the manufacturers you're working with, but if you do find a high total superheat. It's a pure indication that you are low on refrigerant.

You don't have enough refrigerant, filling filling out this whole evaporator coil. You know you have a leak, so then you got to get to searching and finding finding where the leak and the obvious first places to start is at the at the flare joints and you can get away from flaring at the indoor head unit by flowing nitrogen Through while brazing during an initial setup uh, you got to talk to your manufacturer about that as far as warranties go, so i'm not advocating that, but i said you can do it if you flow nitrogen through so you're, not getting oxidation inside the tubing, but you're. Not going to get away from these flares down here, so you're still going to have to do some flaring work on the mini split units, so the superheating begins when it comes out of the out of the saturated phase, changing state and here's your superheat, where the Vapor say: increases from 40 degrees, so it's 40 degrees here, 40 degrees here, 40, 40, 40, 40, the entire time. While the refrigerant is absorbing heat, it is changing from a purely liquid, purely liquid state to mainly vapor and a little bit of liquid until it comes out as a um as a vapor.

That's the phase change, that's the secret to the entire thing working. So you have your superheat there's your total superheat. Once again, if you measure your pressure here, you convert it to saturated temperature, you're measuring the you're trying to find what the saturated temperature is here. Your line temperature will be higher than whatever your saturated temperature is, and in the case of subcoin it's the it's the opposite.

You know you're you're, but i'll i'll go over that, maybe one the other one. You have your vapor travels in through the surface valve back through the reversing valve and in through this little slide mechanism, and then it goes into the accumulator where the accumulator protects the compressor from liquid slugging and and allows the um the refrigerant level to come up. In in the accumulator tank, without the compressors getting slugged, some of these are a single rotary. Some are dual rotary depending on the size of the unit.

That's that one and we'll get into heating mode any questions to find out more about craig and everything he has to offer. Please go to acservicetech.com or subscribe to his channel by searching ac service tech thanks for watching our video. If you enjoyed it and got something out of it, if you wouldn't mind hitting the thumbs up button to like the video subscribe to the channel and click, the notifications bell to be notified when new videos come out, hvac school is far more than a youtube channel. You can find out more by going to hvacrschool.com, which is our website and hub for all of our content, including tech tips, videos, podcasts and so much more.

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