This second video in our two-part series is with craig migliaccio from acservicetech.com. He came down to our apprentice program, our technical school at lake tech and did a presentation on ductless systems, and this part is on the heating side of ductless and mini split operation. So here we have our ductless mini split whatever you want to call it. That's the units these can be ceiling mounted or floor mounted or wall hung units.

We just call them indoor units or head units, and so now we're in heating mode and so we're going to start back at the compressor again. You're always going to have your low pressure, low temperature vapor entering the compressor and then you're going to have high pressure. High temperature vapor exiting and the the pressure change is what increases the temperature and it's increasing the temperature to a temperature much higher than the then. The in this case.

The indoor air and you're rejecting the heat to the indoor air. And if you notice this accumulator, do you notice that there's extra liquid in there? So we did that on purpose and that the whole point is it just depends and especially on a standard uh heat pump. You may have more refrigerant in the accumulator, especially if this coil out here is, is frosted and you're not really getting as much of a temperature exchange. But you may have this completely drained during cooling mode and you may have a little bit of refrigerant in heating mode and that's why also it's hard to tell when you're trying to check the charge of even a single speed unit with an accumulator in heating mode? Is because you don't know how much refrigerants inside that accumulator at that time, and also you know you don't know how much frost is on the fins exactly for the the temperature exchange.

You just don't know how much refrigerants inside that accumulator anyway, so you have high pressure high temperature vapor exiting the compressor, and then it is entering the reversing valve. So right here you have a close-up of the reversing valve. Once again, the high pressure is pushing down on this slide. You also have the so basically the whole action over here which we didn't cover, yet the solenoid uh solenoid valve the solenoid coil.

So i'm sorry the solenoid coil and then the pilot valve what's happening is depending on what brand you have like root and ream or whatever. Now that's different than these mini split units, but depends on if you're powering this coil in heating mode or you're powering it. In air conditioning mode, most single speed and two speed air conditioning units, you're you're powering the reversing valve in air conditioning mode and not in heating mode and then but it just depends a root and ream. They they power it in heating mode.

But anyway, getting back to this, this little mini, reversing valve will put high pressure over here. Pushes the slide this way, because the high pressure here is low, is higher than this pressure here pushes the slide. Also, this force is holding it downwards, making sure that you don't have a leak across here. You can have a leak if you, if you had a field mounted reversing valve - and you put too much heat on this - it can allow it to warp and have a problem right.

There also shards, like a copper shard going through there. That would also potentially mess up that seal anyway. High pressure, high temperature vapor goes through the surface valve traveling into the indoor unit. In this case, your these are both going to be high temperature lines.

This line is going to be insulated and that's good because you would burn yourself when touching it be real, real, real hot and so the vapor enters the indoor coil, where it's starting to reject the heat into the indoor air by having the say 70 degrees inside And then you have your high temperature air exiting this coil after it's absorbed, the heat from the refrigerant after the air has absorbed the heat from the refrigerant. As that's happening, this refrigerator is lowering in temperature. It's de-superheating, it's just the reverse of what a normal. What normally is happening, then you have the saturated state where you have liquid and vapor both exist at the same time.

So this is all just say. This is 100 degrees right here so 100 degrees, and this is 70 degree air where it's sucking in at and so it's going to be able to reject, maybe 90 degrees or something like that air coming out and so what's happening here is then you are allowing The refrigerant to turn into the completely liquid state, it's lowering in temperature. That's your your sub cooling right! There. You still have liquid high temperature, high pressure sub cooled liquid refrigerant, coming back to the outdoor unit, it's traveling through the surface valve into the metering device.

Now this is key because on the standard, single and two speed units you have two metering devices, one's active and one's inactive, and so in air conditioning mode. This one's active and the one inside of here is non-active and there's a little bypass feature. That's built on the inside of the say: a thermostatic expansion valve or a piston is real, easy it just slides on the inside and it bypasses in and around the the inactive piston metering device in heating mode. This is the thermostatic expansion valve.

That's active! That's on this line right as it enters in and then this one is inactive and it bypasses through and around it. The old thermostatic expansion valves had a tube that kind of went around the the thermostatic expansion valve, but now they have like a little ball or a little tab that gets pushed out of the way and the refrigerant can bypass through it through the metering device. But anyway, in this case, you have one metering device. All the time controlled by a stepper motor is checking the the saturated temperature of both coils is checking the super heat, the sub cooling, it's monitoring all those temperatures is also monitoring your discharge, temperature on the compressor and the board is controlling the the the superheat in The subcoin, so it's it's actually controlling this right here, and this is controlling the the super heat really is what it comes down to.

So you have high pressure high temperature, liquid refrigerant entering the eev. That is not an electronic meat expansion valve. That's called electric expansion valve at least most manufacturers refer to that you have an electronic board, but this is an electric expansion valve not as fine of a detail as really what it is on the inside, but serves the purpose you're going to have a little bit Of vapor, mainly all liquid, so the pressure reduction is causing a reduction in temperature. Remember pressure always follows.

Temperature temperature always follows pressure when, when you're talking about refrigerants, so you have your liquid entering your outdoor coil, it's mainly liquid and you're, going to have say we'll. Just call it 80, liquid 20 flash gas, sometimes people bust, my chops and they're, like it's 25 vapor, you know like come on man. You know just it's around that it's around that amount. What does it matter? You know it's close, we're good! You can't see it.

You know so that's what it is: it's 80 liquid 20 flash gas and it's coming in here. It's already the whole point of it is no matter what it is already saturated. That's the point i want you to get after it comes out of the metering device. You have your your your temperature right here is the lowest in the whole system, but really all of this should is going to be the same temperature all the way to here so from here to here.

It's all same temperature because it's saturated, then it can increase in temperature here and it's not going to increase in temperature higher than the the outdoor air temp. So right here you have your it's going to come out as a vapor out of the saturated state and it's going to increase in temperature. So that's superheating super heating, the vapor it travels in through the reversing valve. There's up close shot of the reversing valve goes into the accumulator.

Once again, if the fins are frosted you're going to have more refrigerant in this uh in this accumulator tank, because it's trying to to hold the super heat steady at the outdoor coil and the after the accumulators, it's allowing the oil to get into the refrigerant as Well into the tube, where it enters into the compressor, and the cycle starts all over again 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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