We say suction pressure here we say suction saturation. What's another word for that using the same way of thinking, so we could say suction pressure, we could say suction saturation temperature, but what is it really telling us evaporation? Temperature evaporator temperature boiling temperature? I always ask the this is just an aside, but it's one of these interesting things. What's the difference between evaporation and boiling, i always wondered that because you look at it at a lake, you look at a pond a creek river. Whatever there's evaporation happening, is it boiling? No, obviously, not.

That would be very dangerous. I mean in florida. Actually sometimes it might be, i'm not sure it seems like it is it. You know it's not boiling.

It's evaporating. So evaporation happens just at the surface and not necessarily at the boiling temperature boiling happens throughout the substance and occurs at the boiling temperature so which is actually happening in an evaporator, evaporating or boiling it's actually boiling. So now we have to change the term to a boilerator which doesn't sound right, but that is actually what's happening. It's actually boiling, but for a second keeping it simple, we'll say: evaporation, temperature or evaporator temperature.

That's what refrigeration guys will say if you look on the like emerson, e2 control, that's what they're looking at they're, looking at suction saturation and they'll say: what's the evap temperature on that case, what is the temperature of the evaporator on that case? It actually kind of makes sense so heuristic. What do you compare that to well? An evaporator is a heat absorber. It takes heat in right. So what is the medium that it is taking heat in from the air? That's coming over it from the inside the return air right air passing over it.

So what's the difference between that temperature and that indoor air, that's what we call our td or dtd all right. This is the rule of thumb yeah and i'm going to ask this. As a question - and i really want to know the answer - because every market is a little different, different levels of humidity different types of equipment, if you have 75 degree indoor air, what temperature evaporative, what is your suction saturation generally going to be in this market during The cooling season, okay, there you go there, you go yeah, so you actually do because it is. This is a high humidity.

Is this a high humidity market? This is a high humidity market. Okay, just like us, we actually do see lower tds dtds than what they. What they say, but, generally speaking so if it's 75 degrees, then you're gon na in this market, you're gon na be running more like 43 to 45. Typically, there's two main reasons for that.

The one is because of humidity - and this was the battle with jim bergman - and i don't know if i i never actually fully demonstrated that, because it was this whole thing. It was this really long process over like six months where he would call like every three days it would be. Like you know, seven in the morning i looked down my phone as gym, calling me again, you're, like hey brian. You know you're wrong about that.

It's like okay. Here we go again and it was. It was just a misunderstanding and - and of course i don't want to say, i was right, but i was because in our market we had conditions that he just wasn't used to seeing these very high latent conditions and that does drive up or drive down the dtd. It drives up the evaporator temperature, but the other reason that it happens is also because we have more oversized evaporator coils than we had before as well.

So that's another thing: that's driving it, but it's pretty consistent like it's pretty consistently going to be in that range, and it doesn't really matter much even outdoor temperature, that sort of thing condensing temperature that doesn't really drive it too much. It's really just the energy and that air is driving that boiling temperature creating an equilibrium at around 35 degree td, around there, we'll say between 30 and 35., and so from a heuristic standpoint. That's something that everybody can understand. It doesn't need to be a lot more complicated than that, but then we start to ask the question: we ask very quickly well what are the exceptions? What we say right here: it only works at 400 cfm per ton.

Typically, here we design for 350 and then we have higher relative humidity. So it's going to be a little outside of that in most cases. But you pick up pretty quick and old-timers would say this. They would say a version of it and it was a massive heuristic.

It was a massive uh shortcut which, in the old r22 days they would say 75 degree indoor temperature. What should your, what should your suction pressure, be? That's about 75 70 to 75 right and that just happened to work out like there's a couple things like that. There's a couple little tricks with r22 - that i don't know - i think it was just god - smiling on tradesmen at that time. Maybe they had been especially good for a couple decades.

I'm not sure, but the same thing is true: with heat pumps, you would work on a heat pump and you'd be like well. You know it's our 22 system, it's running in heat. What should your suction pressure be on an r22 system and it's 30 degrees outside about about 30 psi? It's like wow, that's kind of that's kind of strange. Isn't it that's literally just a coincidence.

It's not there's no science behind that. That's just how it was, but then no wonder when we went to 4108 people were like this stuff. Is this stuff? Is the devil? It doesn't work anymore. God is now punishing us, but once you, you know recognize that the pressure number means nothing.

It's the saturation temperature, the boiling or condensing temperature that it represents that matters on the suction side. It's the boiling temperature in the evaporator, the evaporator temperature, on the high side on the liquid line. Specifically, it's the condensing temperature, i'm not going to read through all of these i'll give you guys a little secret. This is like a very little known fact, because it's an app that i made that i hardly told anyone about um.

I have this app called mechpic. It's not hvac school. It's a separate app. It's free, it's kind of like how measure quick, how jim bergman said, mr could always be free, and then he now it's not free it's.

This will actually always be free. So that's a little digging gym there. You know so it's still free, but it knows, but macbook is free and what it is is where i've uploaded all of my photos of everything i've ever done, and i have this chart on there somewhere on there there's a version of it. That goes through each of these faults and the symptoms for each fault that you have at some point i'll put that into kind of its own app in hvac school.

But for now all those images and illustrations and all that exist there and you can even add on there. You can take like an add an arrow to it and add some words to it. Like hey, look at this dummy or whatever, if you want to send it to folks that you're interacting with to do training, that's what it's for it's so that you can upload your own photos and mark them up and then share them with other people in it. So that you can also get all of mine and the long-term idea there is you'll, be able to easily create little mini decks, so you can do your own trainings and kind of voice them over.

So you can be like hey here's a picture of a coil. That's doing this, and this is doing this and now here's what bacterial zuglia looks like or whatever, and you can actually voice over it and it will touch indicate and that version of that app should be out and whoever you know with apps. You say it's going to be out tomorrow: it'll be out six months from now. The point is that, if you want to get into all the specific this causes that type of uh stuff - that's all gon na - that's all there in that kind of full illustration.

You've probably seen it before, where it's got the up and down arrows, and all that and the color coded the key to all of this is just recognizing that the information, the reason why we're doing this is so that we can quickly get to the diagnosis, the Troubleshooting portion as quickly as possible so that we get the main answer. The main thing that's wrong, so that we have enough time to do the rest of it, which those next rest of it are just as important, if not more important. So now we figured out. What's wrong now what caused what's wrong in this particular case, and then what else needs to be optimized in this system in order to make sure that the customer gets the full benefit, the rule of thumb quickly on condensing temperature, we call it ctoa, which i'm pretty Sure is a uh is an acronym that we made up um.

I don't. I don't think i've read that in any books, maybe i have it might have come from dick words, i'm not sure but 15 to 20 degrees. Ctoa on modern systems is pretty typical. It's much more fluctuating than what you see on evaporator temperature, but that just simply means that your condensing temperature is going to generally be 15 to 20 degrees above your outdoor temperature.

When i first started in the trade that whole 30 degree over ambient head pressure, that's actually the way that i was taught to charge systems. When i was in trade school, they didn't teach me super heat and sub cool, they taught 30 degrees over ambient discharge. That's the standard way that they taught and in refrigeration that still holds true in a lot of refrigeration systems. You'll still see refrigeration systems that have that level of ctoa.

Just a quick question: we're going to jump like 37 levels ahead and ask the question: why do we care if our head pressure is higher than it needs to be pressure ratio? Compression ratio will be higher. That's exactly the answer i was looking for. So go ahead. Keep going do you want to stand up here and i'll, give you the microphones? Well, they thank you, yeah.

No, it's compression ratio right. It's the same reason why, having a suction pressure, that's lower than it should be, is a pretty significant problem as well, because the higher the difference between your absolute suction. So your suction pressure, plus your atmospheric pressure, divided by or sorry divided into your discharge pressure, plus the atmospheric pressure, so total total discharge, the bigger that ratio, the greater that ratio, number um, the harder you know the weight, the the the kind of the silly way We'll say it'll say the compressor is working harder. Well, compressors, don't care if they work harder.

That's not the issue, but what it is is that it's running hotter and it's moving less refrigerant through it. So the the techie way of saying that would be. It has a lower mass flow ratio if you have lower suction pressure. The refrigerant coming into the compressor is lighter, it's less dense, so every stroke of that compressor, every oscillation of that scroll takes in less refrigerant and the greater the back pressure that it has to push against the more force is required.

The more energy is required and the less of it moves that's what it comes down to when we have higher head pressure from a very practical standpoint. The easiest way to think about this. Another heuristic is high. Compression ratio equals compressor not moving as much refrigerant, so kind of obvious it's not going to perform as well.

So why? When you look at the performance charts on a piece of equipment, the amount of btus that it moves on hotter days? If you look at the performance charts, it moves fewer btus. Why? Because the head, pressure's higher compression ratio, is higher compressors moving less freon you're going to call freon. That's fine with me. It's moving less refrigerant, right, pretty simple, and when we can get to that level as technicians boom boom boom this that this figure out main cause figure out what could have caused it.

Anything else go through that list and then get it fixed, get to optimization. Now, not only are we a good technician in terms of the technical side, but we're also a good technician in terms of the efficiency side and that's the goal. Have you met the guys who brag about how many service calls they do in a day? I'm sure none of you ever do that. You know you get guys you get guys going on.

It's like well, i've done 12 in a day. Yeah right did anybody know the next phrase that somebody says after somebody says, let's just say it's a junior guy who walks in the group he's like man, i 12, i did. I had eight service calls yesterday. What does an other guy say he says? Well, that's nothing! That's the next line! It's just like! If you go and you uh, you load up the back your truck, say you put a grill in the back of your truck or a load of lumber or something like that and after you get done ratchet strapping it down or whatever you do.

What do you say immediately after you've done that i ain't going nowhere right. If you don't do that, the universe turns into a vacuum and turns in on itself it implodes. Okay, it is required, it's sort of like if you're going to grill some some meats. You know so you're in this summer and you're going to do some grilling and you get it all out.

What's the first thing that you do you go click click right! You have to do that. If you don't double click, the tongs the food will be poison. We know this right, it's just like that. Guys love to one-up each other.

That's the point! Well, that's nothing! It's like telling somebody that you had one wisdom tooth pulled. This is, this is a joke that i'm stealing from somebody else, but you tell somebody that you have one wisdom tooth pulled. Oh man and just wait. That's nothing.

I've had four wisdom teeth or whatever i've had. Eight i've had ten wisdom, teeth pulled, it doesn't matter, but it's the worst possible thing to be proud of right. Why are we proud on how many service calls we do in a day? That is a silly thing to be proud of. What we should be absolutely proud of is that we did an efficient job, meaning we used our time wisely.

We served our customers well and we not only fixed the problem. We fixed the cause of the problem. Then we optimized some people's systems, that's what we should be proud of and whether that's four two six three eight i don't care what it is. If that's what you did, then that's something to be proud of.

You've mentioned call backs. Oh my goodness. Let me tell you if it wasn't, for, if it wasn't for call backs, i would be at least a thousand there possible causes of improper head pressure. That's another key one: is it possible to have head pressure that is too low? Is that possible depends on what you mean by it, but sure it is possible to have head pressure.

That's too low. Perfect example is a couple years ago there were these, these cold snaps that went through the chicago and all the market. Refrigeration guys had just absolute nightmares, because outdoor temperatures were minus 30 minus 40 degrees in that market and all the grocery stores your head pressure. It literally you think of this.

The outdoor temperature is significantly lower now than what you want. Your lowest box temperature to be inside the store in order for matter a substance to move from one place to another place. What has to be present there right? We can say pressure difference, but there has to be a very minimum, a difference in energy state. I mean, even if i take it and shove it from here to there, i'm adding energy to it, to move it from here to there right.

How are we going to get refrigerant to move from low pressure or from from low pressure to higher pressure? How are we going to get that to happen right? There is a point at which it becomes a problem like because we got to figure out how to get stuff moving the direction we want it to move. That's really what we do in this trade we're trying to get refrigerant to move the direction we want it to move at the temperatures that we want it to be at the different points, and that's really what we're doing here so yeah. It is possible to have head pressure - that's also too low, but again we say too high too low. We're really saying is what is causing this system to run in a way.

That's not its design because we're not going to make a system to run better than the engineers who designed it. Probably i guess it could be possible, but they designed it to work a certain way we're trying to figure out what's outside of the design here. Just like capacitors they're designed to fail every three weeks, apparently txvs they're designed to all be bad. Apparently i don't know, i just replaced the txt every time i do a maintenance just replace the txv.

You know just be safe, just throw no one in there. No problem just replace the txv, that's a joke, i'm kidding, don't take me seriously. Super heat, we'll talk quickly about it. What is super heat really telling us? What is it? What is it indicating to us about the system amount of liquid? That's in the evaporator yeah.

That's a that's a really good way of thinking about it. That's that's the way that i talk about in the videos. Imagine a refrigerant stacked in that evaporator oil. How full is it and when you think about this again as a heuristic, our suction saturation, our evaporator temperature, tells us the temperature of the evaporator, and our super heat tells us how full it is.

You know those two things now. You know what you need to know. You can't just know one or the other, because that doesn't tell you enough. You could have a 10 degree superheat and an evaporative temperature that's way lower than it should be or way higher than it should be, and that's still a problem, but if you think of it in terms of evaporator fullness with liquid refrigerant or saturated refrigerant, that's a Good heuristic to use, is it exactly right? Well, i mean yes and no because there's another major problem when somebody says my super heat is 10..

Somebody calls you up. What's your superheat superheats 10., what should be the next question? I just heard a lot of different answers there. My next question: how much money they got so many yeah how much money you got yeah? What kind of cars you got in the driveway? It's a bentley, it's a bad system. No! The next question would be where the where question in superheat gets missed a lot, because is it possible that my superheat at the evaporator coil and my superheat at the condenser at the compressor could be significantly different? Is that possible yeah? Definitely now.

Is it possible on the liquid line too yeah? It is um, but generally speaking, it's not going to be nearly as much of a spread, but it's very possible because where are we typically measuring superheat out of the condenser right? We're measuring at the same place that we hook up gauges? And you know back in the day i remember going to this train. I think it was a train class and they were talking about this topic and the instructor nice. You know his instructor said something about evaporator superheat and it was me or somebody else. I remember it's probably me because i was always a you know.

I was always a mouthy kid at that time and i was like well how do you measure it in the inside? If you can't put pressure ports there and he said well, you should put pressure ports there, like what yeah yeah you pump down the system. Put pressure like what are you talking about? I mean that's ridiculous, so we know that we're gon na measure our superheat realistically at the condenser most of the time. But if we have 20 degrees of superheat outside at the condenser, is that good? Or is that bad? It's probably good, but we could have an evaporator coil, that's if the superheat's 20 outside and 20 inside, and you only got 10 feet of line set - that's pretty low, pretty high sorry pretty high superheat for an evaporator superheat. So the next question is: are we talking about compressor superheat? We talking about evaporator superheat, because you know copeland says they want 20 degrees of compressor superheat.

They want your superheat to be 20 degrees at the compressor. They'll tell you that less than that's actually a problem in many systems, knowing where is pretty significant, what is the job of the txv? Let's get into txts real quick so that superheat right and where does it set it the end of the evaporator? It could be setting the evap, the superheat to 10 12 14 at the end of the evaporator coil, meaning controlling the fullness in the evaporator coil, again go back to heuristics shortcuts in your brain, controlling the level of the refrigerant in the evaporator coil. It could be doing that really well, but then we can measure on the outside and say my goodness. We got 30 degrees of superheat.

We've got a bad txv, two favorite words in the trade, but the txt only has control right there can the txv control superheat. If there's a plug liquid line, dryer no can the txv control superheat. If you have zero sub cool and you got flash gas and liquid line, no, the txp's job might be to control superheat. But if it's not given its prerequisites, then it can't do what it's supposed to do and that's the problem with that statement in terms of a diagnostic term, so the txv's job is to control superheat.

If everything else that we just mentioned is controlled for we're measuring it at the evaporator coil, we have a full line of liquid, i.e, we've got sub cooling, we've got the design sub cooling and we don't have any sort of significant line restriction. I'm going to give you a really for those of you who are more advanced are about to fall asleep on me, because i'm seeing some of you is it possible to have a significant liquid line restriction. Okay, you with me here significant liquid restriction, say a line. Dryer and have no temperature drop across the liquid line dryer or across the restriction.

Is that possible? So i'm saying a significant pressure drop and under what circumstances is that possible? Yes, you could? It could be no flow whatsoever theoretically, but let's say that we do. I mean that would be pretty rare. Let's say that you do have flow. I said no, and i said no in front of a class of people about this size.

I said that you would always have a temperature differential, and i was this is a long time. Did anybody here know joe shearer anybody ever bumped into him, he's on social media and all that he's a he's, a great guy, but he's also a troll, so he's one of these guys who he'll just put something out there and he'll? Let you just dangle, you know, he's got the answer kind of like i'm doing right now. He's got the answer, but he's just going to let you dangle and he's going to, let you say the wrong thing and look stupid and then he'll tell you. Otherwise.

What he pointed out to me is is that if you have excessive sub cooling like massive sub cooling, where somebody kept putting charge in it or whatever - and you have a pressure drop, it can actually eat up that sub cooling before it gets to actually a flash Gas - and you can actually have a case where that entire assembly there is full of liquid and you don't get a temperature drop because getting a temperature drop on liquid with pressure alone see. I always thought that you did. I thought well - and i didn't say this in one of my videos - dropping decrease in pressure. Equals decrease in temperature increase in pressure equals increase in temperature on liquid.

While that is technically true, it's something like point: zero, zero, zero, zero one degree like it's. It's immeasurable you're not going to measure it. Are there cases where you could have no temperature drop across the liquid line dryer and actually have a plug dryer. And the answer is yes because you would say well yeah, but if i had 30 35 40 degrees of sub cooling, i would know that i did right because i'd hook up on my port - and i would see it well - there's a couple brands of equipment where The line dryer is on the inside of where you're measuring pressure so you're measuring it past the dryer.

You know what i'm saying goodman, it's not you know you've seen these right. It's got the liquid line, dryer inside the condenser. Those happen to be the ones that plug up all the time too, might have to do with the fact that you know goodman installers. You know a little different breed, but won't talk about that.

Anybody here sell goodman, just kidding, i'm just kidding, i'm just kidding. We so good nothing wrong with the equipment. Just the installers, i'm just kidding, you'll get those and because you're measuring past it, you may say well. I've got five degrees of sub cool out here.

I've got no temperature difference across the liquid line. Dryer, it's not the liquid line drive, but it actually, there are cases that it can be now. The first indication is that the compressor sounds like you know it's screaming, because it's got head pressure in there that you're not measuring. If you check your current on your compressor, you'll see really high current like abnormally high, because the thing's got compression ratios through the roof.

That would be your indication, but other than that. It's actually really hard to know, and there are these cases like this, that you'll run into so again sub cooling. What's the purpose of sub cooling, yes, tell us exactly how much of a stack of liquid column is there in the condenser lower sub cool means. It's starting to get empty higher, sub cool means, there's more liquid stacked in the condenser.

Are there systems that don't really require sub cooling, yeah refrigeration systems that have receivers don't hold refrigerant in their condenser? The condenser does not stack refrigerant. Liquid refrigerant goes through the condenser. These droplets, they condense and then, where do they go? They just dump into the receiver and the receiver holds the excess refrigerant. So in an air conditioning system, the ones we work on that are receiverless, we're using the condenser to store liquid, but in a grocery store.

Refrigeration system, which we work on all the time you have so much variation in load. In terms of you may some days, you may have one case that needs refrigeration and you have the whole restroom that don't or a hot day versus a cold day or a high low versus low low they're filling the they're filling the cases versus not filling the Cases that kind of stuff, so you have to have massive amounts of backup, refrigerant, liquid refrigerant stored, and so in that case you don't necessarily have subcool. So what is the purpose of subcool when we measure it? It tells us that right. But why do we care? Because we want to know, are we feeding our metering device with a full column of liquid full stop? A lot of people will do this whole thing where they say more sub cool equals more efficiency.

It's a tricky thing because when you increase the charge in your system, so you take a typical system that you guys sell work on every day. Whatever you sell right and you was like all right, my sub cool is low. I'm going to get my sub cool up and you add refrigerant to the system: are you decreasing the liquid temperature, or are you increasing the condensing temperature would see when we say we're getting more sub cooling? What are we thinking we're doing? What do we imagine our head, we're imagining we're, making the liquid colder coming out of the condenser right, but there's two sides to that: math equation that math equation has condensing temperature on this side and it has liquid temperature on the other right. So we can increase sub cooling by dropping liquid temperature by increasing condensing some cases.

It might be a little bit of a drop in liquid temperature, but it ain't going to be much most of that increased sub cool once you have sub cool is going to be caused by increasing your condensing temperature. So it's a trade-off. We actually don't want high sub cool, because what are we doing to our effective condensing area in our condenser, making it smaller we're stacking liquid in that condenser? Now the area that actually does the condensing gets smaller and smaller right. We're making we're giving ourselves a smaller condenser, the more sub cool we get just ringing a bell with anybody cardboard right, that's what you're doing you might as well be blocking the condenser off you might as well be throwing some dirt on it.

You know it's like hey all right, so when people say with every degree of sub cool added the efficiency increases by one percent or whatever they'll say things like that. What are they saying? Why are they saying that first there's two ways that they're correct and one way that it's a lie? The one way that is correct is is, if that additional sub cool is resulting in proper, liquid quality at the metering device where it before it didn't, meaning that if we had 10 degrees of sub cool, we have 10 degrees of sub cool and now, at the Metering device we've got three and we've got good liquid quality versus having five degrees of sub cool and now having flash gas at the metering device. Yes, that is increasing efficiency, simple terms, we need to feed our metering device with a full column of liquid full stop, but if we do that by increasing our condensing temperature artificially, that's a bad thing now. Here's another way that it's a good thing if we are increasing sub cool by dropping our liquid temperature.

How could we do that mechanical sub cooling? Now we don't do that very often in residential air conditioning, but in grocery stores in other areas. What we, what they do, is they literally mechanically cool the liquid, so they make it liquid and then they run it through a evaporator heat exchanger, something like that and they cool it some more well! Now! Yes, because now, when it goes to that evaporator coil, it takes less energy to change it initially to flash it off. You know how we say some of you heard when the liquid goes into the evaporator coil. It immediately goes to 30 vapor 70, liquid.

Some version of that, if you cool that liquid down more, then you lose less to flash gas conversion as a percentage. So is that something that you could do sure we don't in air conditioning much, but you could so when people say that sometimes that's what they're talking about they're confusing information but other than those two things making sure we have liquid quality having enough sub cool. So it makes it up the wall through the attic and all the way over, and you know over the river and through the woods, and then it hits the metering device with liquid or, if you're, mechanically cooling it other than that increasing the sub cooling does not Help it's not a good thing, it's just like saying and you've all had this happen. New kid goes to a job.

Mrs smith is complaining that her house is not cooling properly in the middle of summer. My house is not going you put this new system in and it's not. It hasn't cooled right since you installed it right. They don't all talk that way, but you know i shouldn't.

I shouldn't make more. Mrs smith sound. That way. You know you are blah blah blah, that's from groveland florida, that's what they sound like new guy goes out and he calls you and he says, boss.

I fixed it. Well, what'd you do well. I adjusted the charge right. I got it where, before we had five degrees of superheat and now we have what we're supposed to have.

We got 10.. So i solved that problem right now again. This was back in the day when you know, if you know you had fixed metering devices and you were actually setting superheat by setting the charge. But if we have an evaporator coil that we were filling this much with boiling refrigerant and now we're filling it with less boiling refrigerant to hit a number that the manufacturer gave us did we improve the efficiency? The answer is no.

Now the manufacturer gives us that number for a reason, and so it's good that you adjust the charge to hit manufacturer specs. But if the goal was to try to get her more capacity out of the equipment that did not solve the problem in the same way. That when the new guy goes out nowadays and he says, fix the problem, it only had seven degrees of sub cool and i adjusted to what the manufacturer said, which was 11.. Now we're good right.

No, you actually made the system perform worse by doing that. Now, if that's what the manufacturer said that you need then good on you, it's glad you did it, but you didn't improve the capacity of that piece of equipment unless it was resulting in flash gas at the metering device. Make sense 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.

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