who's not tracking with me on this does anybody have a question that I can answer specifically or not a question what theck are you talking about does everybody understand what we're saying when we when we talk how pressure and temperature are related um how temperature aren the same thing yeah or how we move the heat energy tracking good I love this perfect will the outside air always be hotter or cooler than the refiguring it has to be in order for us to get rid of the heat yeah you have to yeah if it if it were if it were hotter outside than the refrigerant then it wouldn't work it has to but it uh it won't ever be that way uh because wait right right because of just the way if it's hot enough outside that it's like 100° outside then inside the home we're absorbing enough heat energy our compressor will R it up hotter than whatever the outdoor ambient is if if ever the discharge is not hotter than outside your compressor is broken yeah not running um or you have no refrigerant yes so it will always be that way yeah and it always must be yeah otherwise it just otherwise it there's no incentive for it to move and it won't work um let's say that on our evaporator coil so we've dropped pressure and why did we drop pressure cool it cool it 100% we need to change the temperature the only time we're changing pressure in an AC system is because we want to change temperature uh and pressure is our convenient way of doing that we could run the refrigerant through ice get it nice and cold before it comes in and then uh on its way out run it through fire get it hot right we can change the temperature different ways but that's a very inefficient way of doing the same job when you have something that can manipulate pressure you have something that can manipulate temperature uh but it doesn't just change the pressure through the metering device what else happens to that refrigerant the state changes the state begins to change yeah starts to yeah so we have our system that is very high pressure and the liquid molecules are being pushed together they were cooled off so they relaxed enough to form but also the pressure is holding them into that liquid state pressure helps those molecules bond and when they bond that's what we call liquid and so we have both the pressure and the cooling down of the refrigerant so the molecules aren't going crazy then the pressure it's holding it together soon as it drops in pressure now those molecules can begin to to move and separate it starts boiling also we learned that when we drw pressure and the molecules aren't forc together they relax they calm down we call that temperature change it gets cold so that's why it starts boiling is because it immediately drops in pressure and that's why it's also cold because it immediately drops in pressure [Music] who can give me the three phases of matter the three the three main phases of matter does everybody know what those are cool awesome where am I going to find solid refrigerant in my system maybe Freez solid refrigerant Oh no you're not never right if I have we have freezing in AC what's freezing water yeah and where's that water coming from condensation and where's it coming from the air the air air exactly what we're breathing right now it's plenty of moisture in there to make a coil coated completely with ice giant chunk of ice going to take 6 hours to melt sure is a heat and that's all that moisture in our air condensating freezing but the refrigerant never freezes no they should not uh if you're refrigera is sell then you have bigger problems like the end of the world um um so in our system we have we we only ever see liquid and Vapor um liquid refrigerant we're going to see in our condenser and going into our M device as soon as we pass through here we still see some liquid we're boiling we're evaporating in here in the evaporator and turning into vapor so the these the job of these two components is in the name right like pretty much everything is it's it is those are intuitive the way they're named it's not not a trick right the compressor compresses it condenses in the condenser it evaporates in the evaporator uh those you can trust this one I'm not so sure about it meters the flow yeah but it's called a metering device we also call it a te or TXV you sketchy it's a little bit harder but it drops pressure but we see so phase change is very important to what we do uh we have components where we're changing phase of our refrigerant right and there's there's a trick here that lets us move heat energy really efficiency efficiently right so we have liquid and we have gas um I can manipulate withth so water boils at 212° F right and water freezes at 32° F but uh what you see on the slide there is a phase diagram so I can change the temperature at which water boils or the temperature at which it freezes by manipulating the pressure and the temperature so Bert had a story um not too long ago he went camping right and he had you want to tell the one about Colorado in the oh yeah sure sounds great um I went actually North Carolina and we were up about 5,000 FT elevation on a mountain and uh they had the same um electronic boiler that I have at home when I made tea and at home uh I set my electronic boilage to 212° so that when the water hits 212 the alarm goes off and I'm ready for tea and 212 is where water boils right okay so then I went up in the mountains and they had it set to 208 and I was like okay somebody doesn't like their hot tea put it on 212 started it the alarm went off I came in there was no water does anybody know why there was no water left te CH pressure pressure cuz you're on a higher elev okay what did the change in pressure do to the boiling point okay decreases yeah I was just going to say like when you have the lower pressure like all the face changes lower there's a lower pressure and then it just it it boils off and then it's the same with the refrigerant because it's weird that was what was that's what's confusing to me before because I was like why is it boiling at like 35 degrees and then it's condensing at a higher temperature like that's that's whack because water boils at a higher temperature then but then I realized oh that's why we have the metering device that's why we have the compressor because that's it's allowing it to do that when we change pressure so I can change pressure or I can change temperature and I can manipulate the point where that phase change happens did you got uh did anybody see the uh at the HVAC Symposium when the guy was boiling water at at the Ed room temperature yeah yeah you saw that one uh I don't know if the videos are up yet but basically if you ever seen this in science class they'll do this thing where they'll take a beaker of water and put it under a bell jar and pull a vacuum on it and all of a sudden it starts boiling right because you've changed the pressure things will boil at room temperature if you decrease the pressure right you can do that with water it works with any substance right it works with refrigerant so when we change the pressure we change the point at which it boils or or condenses right we can also ramp up the pressure and make that condensing point a lot higher right that phase change is going to be critical to how much heat we can move because when we're boiling or we're condensing we're actually moving a lot more heat energy than when we are just gaining temperature right that that there's something magic that happens that boil boing right Beyond just bubbles so back to the uh T story if um if boiling point happens at 208 where I was in my elevation then what happens is I'm putting tons of energy heat into that water it's heating up right as soon as it hits 208 it starts changing State all the heat that I add to that water does not make it go above 208 it stays at 208 because whenever something is changing state it doesn't change temperature until it finishes Changing State so now all the heat that I added to that water was being used to boil it but it wasn't being used to change its state at first the water was uh 70° dump 70° in there start adding heat I'm adding tons of heat it's slowly coming up in temperature to 208 it begins to boil every bit of heat I add changes the temperature while it's a liquid but as soon as it goes into saturation where it's now Changing State still a bunch of liquid but it's also boiling all the heat that I add doesn't change its temperature stayed at 208 and all the heat I added was being used it was being absorbed and being used to boil it so by the time that uh it finished boiling all the rest of that liquid then there was nothing in that teapot except for vapor and it went up to 212 really quick you added heat it went up to 212 it became super heat and you can't make tea with super superheated liquid it's just air so um that's what happened to my tea so then I had to restart and put the timer at 208 so once it hit its boiling point it let me know and I had water in there which also means that I now have to make my te at 208 temperature in order to make my te at 212 if that was crucial I would have to boil inside of a pressurized tank so you guys have heard of pressure cookers right that's so that we can make our boiling way higher it holds pressure and as you increase the pressure you increase the boiling point so water inside there could get to 300° without boiling and we do some really fast cooking um under a pressure cooker so same thing with refrigerant the reason we use refrigerant instead of water in an AC system any ideas it's easier to manipulate lower boiling point yeah lower boiling points yeah yeah it's easier to manipulate because it's lower boiling points because refrigerant boils at 212 at 0 psi do you know what temperature it takes to boil fora at Zer PSI let's find out all right you don't need the uh the gug more if you look up at the screen this gives us a digital but I like the gauge because you can see the range you can see the whole thing as you change pressure you're changing and that one's more fun because you can actually change it as you change pressure you're changing the boiling point right yeah so here at Z PSI 48 minus 60 see that so water boils at 212° at 0 psi refrigerant 42a boils at-60 at Zer PSI huge difference much lower boiling point which means we can manipulate it for some sweet cold temperatures that we can control water we could do the same thing but we' need equipment that could handle really high levels of PSI and really low levels of vacuum we would need some very extreme equipment one creating a vacuum one creating um well we would have the high PSI whenever we tried to smash water yeah so or Vaper so um we're just going to reviewing as great we're going to step back because I just heard my system come on okay and um and we're going to we're going to cover this again in a little bit and we're a different Yeah a different angle I was going to tell you don't be afraid to ever go ahead okay because review is totally cool if the explanation naturally leads you into deep step that we're going to hit again gota we're going to go play with satation and stuff like that but I think we'll just finish this up for now um so uh we we talked about pressure at the beginning um we let's talk about suction pressure and section saturation real quick um so got our we usually take our pressures at our condenser right when you're doing your diagnostic you've got a you got the big line right which is your suction line you got the little line which is your liquid line um section line is also sometimes called the vapor line the discharge on a system is inside the condenser unless you're on an r2u you can actually open it up and grab it which is convenient but for us it's locked inside the condenser you can't go put your hand on it while it's running so I brought the discharge inside so you guys can touch it it brought straight from the compressor this line inside how did I bring it inside heat mode heat mode go we have an R20 uh R22 I know we have a heat pump system and uh the reversing valve switch the direction flow from here to here and so our suction Line is now our discharge I'd like everyone to jump up real quick and carefully touch it it will burn you if you hold your hand on it it's hot enough to make you dance if you hang out and we're going to do another round of guessing that one's not bad the other one was terrible nice and warm huh anybody want to guess 119 119 the pil 130 130 136 36 you know what your water temperature is at home when it's hot uh should be around 120 120 is like a a standard that's hot that's hotter than your water no it's just kind of a standard people will sometimes go up in the 30 scolding before you get change all right I it's it's a suction line when first started touching it it was 150 um it's rapidly climbing because it is both warm outside and and warm inside so 162 right now on the suction line that's your discharge temperature yeah like I said it was 150 when you first touching in heat uh you can see our pressure bad or pressure is maybe just a bit higher right yeah about 100 PSI higher is that is that on the section side no it's on the liquid okay but it's liquid here met it's a cheat yeah uh so the point that I want you guys to take away is that line you felt that was um 40 something degrees eight 48 degre is the same heat that you're feeling right now in this line just different temperature different temperature same heat so the compressor took that and smashed it and put it out on the discharge line you touch that you think oh wow there's way more heat here than there is on the suction line no same heat uh it's just way higher in temperature that heat came from our suction got smashed and became 160 we didn't add heat to it we just smashed it we just increased its temperature same heat just wanted to get a little Vis when you touch something and it feels cold to you it's because that area of your body lost its heat like you said that heat went into the suction l so when you first T it you don't have an accurate reading of how maybe how cold you think it actually is as more of that heat in that area leaves your body and moves into it your nerves are picking up like holy moly what happened your temperature sensor calibrated you're not actually feeling temperature C you're not actually feeling the P line like we think like oh my body's feeling that it's cold now your body's feeling the heat leave your your hand say taking a hot shower and you're cold right that's exactly right mhm that's why longer the L except for now Heat's going into your body exactly so you felt cold before and the water was hot once you got in it if they want in it for a while body your body when you take a c you're just like rejecting heat from your body all right thanks for the interruption for real let's hang out with suction long enough to feel comfortable with the rule of thumb and all this it's really good okay very useful so uh first let's divide our our system we've got we've got two sides that we usually refer to we've got the okay so there's a line right down the middle here this is the low side and this is the high side right good job this is low pressure this is what good you're good at this you are we just had a little oops and that look way better yeah high side low side right so I need I want to know the pressure on my low side is going to be the same from here to here right all through the evaporator coil all through those lines it's always going to be one pressure same thing is true on the other side after at least my compressor all the way from the compressor back to where it hits the metering device that's going to be the same pressure throughout all of it right so when we're taking pressures we measure our low side pressure and we measure our high side pressure right and we can do both of those at these little ports here at the condenser right that's the most common access point in residential systems so we uh but when we're taking our pressure at our ports uh my section line when I put a pressure probe here on my suction line service for I'm going to get the pressure for my evaporator coil for everything here like all through this line so let's name these lines real quick actually it at the end but does anybody know the names of all the lines all four yeah I think so Okay who wants to give it to me go for it is it discharge okay where's the discharge to the compressor to the condenser okay discharge and then uh from the condenser to the m device section from the condenser to the Ming device no no not sectionid okay I got liquid line all right section line would be from evaporator to Condor and then here's the tricky one that most people don't know what's that one called yes expansion L there we go look this guy The New Guy Somebody went home and was watching some videos last night the expansion line so most of the time you don't see the expansion line because in residential systems your metering device is mounted on your evaporator coil so your expansion line is about this big this right here yeah this is an expansion line on a most U most coils does anybody know on what kind of system I can see my EXP expansion line very long expansion line I mean don't you see it on you see it on carriers I mean you see the thing and it splits off oh yeah you can see it yeah you can see it I mean like which ones have a long line yeah oh long line say package units no that be train Min splits Mini Splits who has worked on a on a mini split system before I have yeah K I know you've installed them you've installed them alons you've seen them cool so mini split systems there's still two lines coming to and from your condenser but in a mini split your metering device is actually in the condensing unit that indoor unit is only a coil so what that means is that if we're getting metered in the condensing unit that second line that's going to the coil is the expansion line that whole long thing right is filled with saturated refrigerant what what happens when we drop pressure what happens to the the temperature of this this a lower temperature lower temperature right and uh how low how how how cold any ideas uh it ranges probably close to 35° 35 to 45 that's usually range and how cold our our saturation point is how cold our lines are yeah and we've started boiling it's still mostly liquid but when things are that cold in our world what do they do when that I say you insulate the lines yeah exactly right so if you ever look at a deckless line set both lines are insulated because both lines will condensate that makes sense right uh on on normal on normal residential split systems like you'll see here we've got the section line insulated but we don't have the liquid line right because it is a liquid line it's not going to condensate but on a deckless If This Were a deckless system both those lines would need to be insulated because one of them is actually the expansion line and the other one is still a suction line and they do that because they can duckass are made to be compact right really tiny as little as you can put inside the better so they put the metering device outside um more room for it out there than on the inside unit so let's get back to suction pressure yep um so we've got our high side we've got our low side uh if I put my Probe on my on my suction Port uh at my condenser I'm going to know what the pressure is all across the low side of my system um the only reason I'm looking at pressure is because I'm really curious about what the temperature is inside my evaporator coil looking for a magic number called my saturation temperature right uh saturation temperature is the temperature at which the refrigerant is going to boil or condense depending on which way I'm going so in my evaporator coil I'm looking at what temperature is it going to be in that coil when my refrigerant boils that is my suction saturation temperature and when you're doing Diagnostics I got a rule of thumb that I like to use which is I want my suction saturation to be 35° give or take about 5° below whatever the indoor ambient temperatures which I can measure at my return PL or with the return probe if it's got like a temperature so 35° should be the difference there okay and that's designed by um you know when manufacturers are designing equipment they're going to size the compressor the metering device the size of the coil and CFM to try to hit that balance point that 35° balance point and you have plus or minus on there because you you're changing there's in the real world you have CFM changes you have a little bit of refrigerant flow changes um but yeah and if I have so there is a little bit of play there but if I see significantly low or significantly High then that is an indication for my my diagnostic that something's wrong if I've got low suction saturation I can have an air flow problem I could have a charge problem if I have Sugen saturation that's much too high I might have a fan speed that is set too high right I'm not again I'm not balancing my heat load with my refrigerant circuit word so he has the 35° below indoor ambient temperature what's another word we use more commonly in the trade for that indoor ambient room temperature no dry we do use room temperature a lot indoor Dy but dry B okay those are all the same thing but there's one we use more commonly when you call someone for a teex support they're going to ask you what is my who said it the delta T okay it's part of the delta T it's half of it we have our supply and our return return return air yeah return is the other version of saying indoor ambient or indoor driveable or room temperature sorry the return is the most accurate so you could walk around in here and have 68° the return is pulling from the ceiling could be 78 depending upon how high your ceilings are and how much heat there is in the space so the return is the accurate place to measure from what my system is taking in as the indoor ambient from my return a 35 Dees above that should be my suction saturation uh a lot of times people just look at the thermostat thermostat reading that's the indoor indoor Ambient Air Temperature but it's not as accurate as actually putting a probe and seeing what's really going into the system because the thermost step might be off or it might not be able might not be taking into account the fact that there's a hole in the Attic duck work somewhere you know so um we meas we with those two things we can figure out are we within our rule of thumb my return air temperature and then looking at my suction pressure which on measure quick you can see on this dial you see that pink the pink ring mhm right that pink ring is giving me saturation temperatures and those correlate to pressures on the outside dial so the outside dial is giving me PSI that pink ring there is that yeah yeah so that pink one is giving me at this pressure what is the saturation temperature and you can see that on measure quii right if you look when you look at the the measure quii has the dial set up just like the analoges because that's what everybody knows so that Center number that's in the center of your dial is your saturation temperature right the number below it is a PSI is a pressure they are always correlated right um You can can see that on a that's the reason we have PT charts right is there's always a temperature a correlation between pressure and temperature and it's mapped out that's why if you ever so when we play with measure quii right as soon as I put on my probe right it'll give me not only the pressure but also a saturation temperature that then correlat to that pressure it's got programmed in it that PT chart this is a visual PT chart right I see that there is a COR wherever pressure I'm at there is going to be a temperature associated with this that is that that is the saturation temperature my refrigerant will change state so let's say you called me and I said what's your evaporator temperature and um you were like I don't have access inside the house I'm like okay your gauges hooked up yeah okay so your suction should tell me what your evaporator temperature is well how how can we know from outside that our our on our suction what our evaporator temperature is hold L side and the saturation exactly one it's all the same side it's low so we're measuring the same PSI inside the evaporator as we are out at the condenser right but if we have if we know what that PSI is somebody give me a suction number 139 139 nice and warm I'm going to get up okay I'm just going to get 125 that's easy for me to find 125 139 at 125 what's our saturation 42 42 boom so uh if saturation is happening somewhere in our unit and our PSI is 125 then we know wherever saturation is happening it is exactly 42° because that's what our pressure is they are always tied together this is a very consistent constant constant science so if our meter device is creating saturation creating the boiling point and that saturation is happening as it travels through the coil until eventually it finishes and becomes fully Vaper then we always know based on the temperature or the pressure what temperature our coil is now if our coil was not in saturation let's say this system's off it's not running and we still had 125 psi we would know at 125 psi 40° is where saturation happens but because the refrigerant is not moving it's not flowing it's not actually in saturation we're not boiling we're not actively boiling but if we take that refrigerant sitting there at 125 40° it's still in saturation you add a little bit of heat to that it's boiling you remove a little bit of heat it's condensing it's still in that mixed state at 40° if we measured it above 40° we would know whatever is in that line is not saturated it's vapor if we took our clamp when we measured it it was still at 125 psi and we measured it and it was 30° we would know that line was full of liquid if we measured it and it's 40° we would know it's in saturation it's in the mix state it has both vapor and liquid is that constant to 40° it's going to vary at 125 psi constant yeah so wherever it's 40 pressure wherever it's wherever it's at saturation it's going to be 40° at 125 psi soon as and you can see on here as soon as you change the PSI you change where that point boils at and that goes back to what we were talking about with the phase change right we can manipulate where that boiling point is based on the pressure right by either dropping it or increasing it and so then I'm I'm going to ask one more question to see if it s sinks in if I take my clamp on a system that's running so we know saturation begins after the metering device and goes through this system it's in saturation if I take my clamp on a running system here and it says 46° I'm going to go on the expansion line on one of these little lines right here after the metering device boom 46° system's running it's in saturation my suction clamp says it's 46° line expansion line is 46 what's my PSI 13 all right let's go find it boom there's my PSI right yeah got do that you you know your PSI because you know saturation happens it's happening right here in the circuit this is where saturation happens I measured the temperature so then I know that always if it's in saturation that always has an exact PSI that's connected to it or we usually do it the other way around we usually the only reason we hook up one of these bad boys where did that go oh yeah it's on the screen the only reason we hook up one of those bad boys is not because we want to know what the PSI is we don't care about the PSI we just want to know where the saturation is what's the coil temperature where's the saturation point or if you had just as easy access you could always put your line clamp on The Equalizer tube and get your PSI but usually it's a little easier access to hook up the port right there that's on a running system that's doing its job if you have a running system that's flat then none of these rules apply right we're not actually have we don't have liquid where we should have it we don't have saturation having where it happens um but on a system that's running you grab the line it's cold beer can cold liquid Line's a little warmer compressor is moving refrigerant all you would need to do is hook up your um to the equalizer tube where there's saturation happening and you could figure out your PSI that's uh so you'll notice a lot when you call people for tech support they're going to stop asking you things what's my section suction pressure you're going to hear things like what's my saturation what's my evaporator temperature that's really a number we're after they don't make like PSI doesn't mean anything to them that mean you're they want the extra step where let's go and give you the saturation temperature which you can look up on your PT chart or measure who wants that do it who are you saying wants that any anybody that you're calling for tech support they're going to be oh tech support yeah or so that means uh if you're on the phone with somebody for a company or with one of us and we're getting you we're trying to help you out like I'm curious about the section saturation if you tell me it's 150 psi that doesn't even mean anything to me I'd have to look it up so you give me the suction saturation temperature that means something I'm trying to balance temperatures not pressures can we um mhm have them calculate where the suction ESI should be all right what's our return 69 all right 69 it's a party it feels a lot warmer than 69 in here what's our Thermostat say it is so we can't check we can't trust this room's ambient why is our return 69 you guys can figure this out wait what are you say our return is 69 that's air going into the unit but if we look at a thermostat it's 74 here and it doesn't feel like 69 in this room the return is okay so the return right up there you think it's 69 up there but it's 74 here you think the top of our room has hotter air it would be hotter up there than 74 so that's not why any guesses look at the size of that return you got like a 10 Max maybe an eight is that enough for that whole unit no you need more so we do have more this unit is cooling many other spaces that are right now enjoying the heat I turn on or when I turn the cool down super cool so there are return turns in all these other office spaces pulling air and those office spaces are 69 or colder so we have RS in the mix but a lot of other Returns the rest of the office is experiencing some cool temperatures thanks to us being in the room where the thermostat is we're heating up this room it's trying to keep up they're all freezing out it's 69 in the return because it's pulling from many other rooms and all joining together in that column so you can't just go we were to do our 30 5° based off 74 rule of thumb he just taught us our suction saturation should be 35 below our indoor ambient we just went off the thermostat we would have very inaccurate but we plug into the return now we know when our system is experiencing all right so now rule of thumbs what should my suction saturation be if the return is 69 what 41 41 okay wait is it yeah it's like 6 it's like it's a range not no we're we're just going to go with the exact first we can do plus orus five but let's go with the exacted right here 34 34 why does that feel so perfect you guys are so good at math it's amazing all right all right so if it is 34 then you two can have a look at this go ahead if it's 34 saturation then what should my PSI be when I hook up to my unit like 103 wait uh like 100 11 they go by increments of five right I have no idea little line you're on your own just give me something like just over 100 105 106 yeah so if you were to hook up to 105 106 you might be like that seems kind of low because we're just thinking PSI we're used to see a little higher than that that seems kind of low it's not low for the 69 degrees coming into this unit that's right on target so knowing what it should be before you hook up is is uh actually makes your test valid if you don't know what it should be when it hooks up you shouldn't even be hooking up so this is a really important one to hang on to plus or minus 5 degre but um what what is the hot air coming into the unit and plus or minus 5° from 35 I should have my suction saturation we're going to look at the same thing on the high side just briefly where it's the same idea right we're hooking up to our liquid liquid Port this time for the same reasons or discharge or discharge ah well yeah or discharge yeah if you had a port on your discharge line then yeah you it there too it's just a lot of uh these guys in commercial don't even have liquid right that's true that's true um but it's still the head pressure yeah so that's that whether I take it at my discharge line here or if I take it at my liquid line here it's going to be the same pressure throughout again right and we're doing it for the same reason I want to know what my saturation temperature is this time in my condenser so again I I want the pressure which correlates to my saturation temperature same thing is on the low side only now I want to know what's my condensing temperature so I'm going it's going the opposite way instead of boiling I'm condensing now but the idea is still the same where's my saturation so that way I can do some calculations and again I have a rule of thumb uh based on outdoor air temperature um somewhere between what I write 13 to 20 plus or minus 3 something like that that one's a little bit more a little more range depending on condenser size um and fin size or condenser fan size speed against fan we're not trying to get as exact yeah inside we want it exact cuz we want to dehumidify we want perfect Comfort outside we just need to get rid of heat yeah it has to be hotter basically I my my sorry my coil is my coil is what I'm mostly worried about I'm calibrating my system based on that this is sort of a consequence right this I just need to make sure that it's hotter hotter than outdoor by a good margin so I can reject heat efficiently other than that I'm not worried about my coil freezing or something like that thanks for watching if you're willing give this video a thumbs up and drop us a comment don't forget to hit that Bell icon to stay updated with all of our future videos and as a quick reminder HVAC school isn't just a YouTube channel dive deeper with us at our main website hvacr school.com curious for more knowledge on the go we've got you covered tune in the HVAC School podcast available on all your favorite podcast apps and while you're at it join our thriving Facebook group also don't miss out on our free mobile applications available for both iPhone and Android we're all about 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