Hey there, thanks for joining us on this attention-deficit version of hvac school, for those of us with shorter attention spans who want me to get to the point quicker. I get a lot of requests for very simple training topics and that's largely what we do on the HVAC school podcast. Actually, before I go any further, I need to remind you that this podcast, like all the others, is brought to you by our sponsors, which is carrier. Rector seal and Mitsubishi comfort, and also I have to mention test out test - has been a long-term partner of HVAC school and Parker's Portland and the Zoom lock tool.

Also so those are our partners they're, the ones who make this possible, but I want to do these kind of like very quick episodes, just as quick recaps of things that are very important to the trade, they don't require a full podcast. Now there is a full podcast on the basic refrigerant circuit way back, so I don't just months and months ago, you can go back and find that you can find all the tech tips by going to HVAC our school comm. But I want to quickly for those of you in school, those of you who are new tax or older tax, who just forget this stuff, we're gon na go quickly through the basic refrigerant circuit, so start with a compressor, so the compressor. What does it do it? Compresses, the names of these things are just amazing.

Now, what's interesting, compressing and pumping right, can you pump something without compressing it, and the answer is yes, because liquids are largely uncompressible, you don't it's very difficult to compress a fluid, but you can compress a vapor. So compressing a vapor means that you take something that takes up a larger volume and you force it into a smaller volume, which is what a compressor does. So it simultaneously moves and compresses one way that I've heard this said that helps you kind of think about a compressor and how well it works or how it works, and when you think about compression ratios and all these more complex things is that a compressor both Compresses refrigerant and it moves refrigerant, the more it has to compress it, the less it moves it and the less it has to compress it the more it moves it if that makes sense, it's an inverse relationship. So, if you compress more, you move less.

If you compress less, you move more and you'll notice. You know when you look at a compressor. The large line that enters the compressor is the suction line. That's the the cool vapor, it's a less compressed entering it, has more volume more space and then, when it comes out of the compressor, it goes into a smaller discharge and that's that's by design.

So a compressor is taking a larger volume of refrigerant by mass and it's compressing it down into a smaller volume. Now, what you'll notice in a compressor is that the refrigerant going into the compressor down the suction line is cool vapor and when it comes out of the compressor in the discharge line, it's hot vapor and a lot of people think oh well. The compressor is making it hot well, primarily, what's happening, there is heat of compression, so when you compress something you're forcing those molecules together into a tighter space, so if you imagine you know, I always talk about it in terms of like ping-pong balls or bouncy balls That bounce perpetually, if you take these bouncy balls and they're, bouncing around very slowly and you pack them into a smaller area, which is what a compressors doing it's taking, that that volume that mass and it's compacting it down into a smaller space. Now those bouncy balls are going to bounce around a lot faster and there's greater friction and therefore there's greater heat.

And so that's that's a way for you to kind of. Remember that why that occurs. Is that when you compress something you increase its temperature because you're decreasing its volume, so the first first component that I always talk about, I always do this in order is the compressor. So you go through compressor, condenser, a metering device evaporator.

Those are the four components and then there's four lines, which is the discharge line, the liquid line, the controversial one, which is the expansion line and the suction line. There's a couple different terms that are used for the expansion line. But that's what I call it, and so what you want to learn as very early on in the trade if you've never learned. This is how to say those in order very quickly: compressor, condenser metering device, evaporator discharge line liquid line expansion, line suction line.

It helps you envision this whole system, because what technicians often do is they'll think, oh well, I got a compressor. I can see that, but I have an inside unit and outside unit. Primarily, you know they'll talk about the air handler or the furnace, but just remember: you've got four components. They can be distributed in different places in the system which you will see if you're working on our rack or parallel rack refrigeration system, for example, versus a water source heat pump versus a ducted condenser air unit that they make it's called a room top unit.

You know the components can be in different parts in different places, but you always have in some way or form one way, shape or form these four components and they're connected together with these lines. Okay, so you leave the compressor and go into the discharge line and the discharge line is of hot vapor and it enters the condenser. In some cases it goes almost straight out of the compressor right into the condenser. In some cases you may have a heat pump system we're going to have a system that has a muffler or could have a reversing valve like I said, if it's a heat pump system, so you may have some other things in that line, but it goes out Of the compressor and into the next primary component, which is the condenser and a condenser, doesn't have to be a typical tube, thin condenser like we're used to seeing air-cooled, condenser and residential.

It could be a water cooled condenser. It could be a tube and plate heat. Exchanger, it could be a lot of different types of methods of exchanging heat, but what a condenser does, what its job is again obvious name is to condense, so it rejects heat off of that refrigerant. Initially, when it comes into the condenser, it's a highly superheated vapor.

It has to reduce that superheat, so it has to get down to the saturation temperature and then it will start to condense, and then it gets down to the point that it starts to sub cool. What all of these things are a kind of whole separate podcast, but just understand that it goes into the condenser. It D super heats. It condenses completely from a vapor to a liquid, so it starts off at you know: one percent liquid and 99 % vapor, and then it condenses down and you'll notice in most condensers.

It feed the vapor feeds into the top and it runs through the condenser and it comes out at the bottom because, naturally speaking, you know, you're gon na have a vapor which is lighter, less dense and as it goes down, it's going to become a liquid. So as that heat is rejected off of it, it's gon na fall down and it's gon na come down to the liquid line, which will be generally down at the bottom of the condenser. So there's three different things that have to happen in a condenser. This is worth memorizing if you're gon na take an a test or something first, you D superheat, you drop the temperature to the saturation temperature and also known as the condensing temperature.

You fully condense, fully change state from vapor to liquid, which is the bulk of the energy exchange, occurs there and then you sub cool and generally speaking and most of the systems we work on and and are residential and light commercial careers. Is we see, you know 10 degrees, 10 to 14 degrees of so cool? That's what we'll often see, and that means that it's dropped its temperature 10 to 14 degrees below the saturation temperature. So it's fully liquid and it's still dropping temperature once it's fully liquid gets. What's line, it goes into the liquid line, so the liquid line then travels to your metering device and keep in mind your metering device is not always inside we're used to seeing it inside a piston or cap tube or a expansion.

Electronic expansion valve or thermostatic expansion valve there's a lot of different types of metering devices, but in some systems those in some split systems like ductless systems, the metering device may actually be outside in the condensing unit, and so it can be long. It can be short, but you always have a liquid line and that's the line that that the liquid travels in before it hits the metering device. It should be sub cooled liquid, meaning liquid, that's below the saturation temperature fully liquid. Then it enters the metering device and within the metering device, there's a pressure drop, a significant pressure drop and that significant pressure drop allows the refrigerant to begin to boil in the evaporator coil.

So we use the phrase evaporate, which you know there's some dispute on whether or not that's technically correct, but the best way to think of it is that that refrigerant is boiling in the evaporator coil. There are several different types of metering devices that exist, but their job their purpose. Their intent is to create a pressure drop and there has to be a sufficient difference in the pressure and the liquid line in the desired pressure and the evaporator coil for that metering. Device to work properly again, that's a more in-depth conversation on metering devices which we're going to do in a separate episode of these kind of quick technician tips.

But generally you just need to know the job of the metering device is to create a pressure drop and during the evaporator coil, so that that way the refrigerant will begin to boil in the evaporator coil at the proper temperature. Now for us in the residential, like commercial, typical air conditioning world, we're generally going to see evaporator temperatures of around 40 degrees. Now it varies based on some some factors, one of the biggest factors being the temperature of the indoor air flowing over that of Aperta coil. But you're going to be generally around 40 degrees in that, if a protocol, we can't allow the evaporator coil to drop below 32 degrees in comfort cooling, because then we're going to start building up ice on that evaporator coil.

So we have to create conditions under which that evaporator is boiling refrigerant inside of it at above 32 degrees, but still also a low enough temperature that we can transfer heat out of the air that's flowing over that of a protocol. So your indoor air obviously flows over that coil on a tip, Comfort, cooling, application and it's absorbs heat into that of a protocol. I give a test for technicians and one of my kind of questions that trick a lot of text. As I say, what component in the air-conditioning system absorbs heat? Well, that is the evaporator coil.

The evaporator coil is designed to absorb heat from the inside space and people think well, it's cold well, exactly when something is a lower temperature than the space around it. It will absorb heat from the space around it into that of a protocol, so the heat from inside the house in the case of comfort cooling, is absorbed into that of a protocol, and now it begins to boil, and as it boils it will, it will go All the way from the beginning of the evaporator coil, all the way through the end of the evaporator coil and boil up until it gets to the last couple rows and it will begin to superheat, and so when refrigerant is boiling, we also say it's at saturation. So if you look at your gauge and you look at that needle and that pressure that you see on that needle on your section gauge - that's going to be a very close proximity that there's some change that can occur with pressure drop. But, generally speaking, it's going to be right in that same vicinity of the boiling temperature of that refrigerant at saturation in that evaporator coil.

But once it's fully boiled once it's no longer boiling, then it can increase in temperature and that's called super heating. So when we see something that's superheated, what we're saying is is we're saying that it is no longer a mixed state. It is no longer in the process of boiling or changing. It is now fully vapor.

So something is superheated is fully vapor. I heard somebody say it's like Superman: he flies above up in the air and so that's a way to remember. Superheated means up above and it's above the boiling temperature, whereas sub cooled means cooled below the liquid temperature, so you think of submarine. So if it's a fully liquid and it is cooled below that that would be like sub cooling, which that kind of stuck with me, it's a good way to remember that.

So once it's fully done boiling, it leaves that a wrapper, a coil, travels back down the suction line. The suction line also called the vapor line in some cases, travels back to your compressor. It's it's sucked back to the compressor. That's kind of the way from a resection line and vapor line is obvious because it's a vapor and it's going to be a low pressure, low temperature, vapor traveling back to the compressor and it's important that that suction temperature is superheated, meaning that it's because if it's Not if it's still boiling you're going to get liquid back to the compressor, which can be very damaging, but you also don't want it to be too warm because the compressor most compressors, that is our refrigerant cooled and which means they utilize.

The temperature of that suction vapor and the mass of that suction vapor to help cool the inside of that compressor. So if you don't have the proper mass and if it's not of a low enough temperature, then the compressor can overheat. So it's something you did you definitely want to control. Is that section temperature, which is one of the reasons that you've noticed that suction lines are insulated, beside the fact that they would sweat and on a heat pump? That would be an actual efficiency loss.

But that's one of the money feof many reasons that that is an important thing to do is insulate your suction lines. So they don't pick up too much temperature if they pick up too much temperature. The temperatures too high that can result in compressor damage. So that's it and compressor out of the compressor high temperature high pressure discharge gas into the condenser, where it D super heats condenses which is at the saturated State, then turns to fully liquid.

Where it's sub cools, then it goes into the liquid line into the metering device, which can be many different types and in many different locations out of the metering device. It hits the expansion line, which often really isn't a line at all. It's more just a direct connection. In many cases the metering device is coupled directly to the evaporator coil.

Then it goes into the evaporator coil, where it flashes or boils once it's fully boiled. Then it super heats which proves that it's fully vapor then back down the suction line, which the temperature must be superheated, but also not to high temperature as a result in trouble with the compressor. So that's it for now. That's the that's today's quick tip! These are always going to be in addition to the regular podcast they're, not gon, na replace any of the regular podcast just some quick.

It's quick tips for especially for those of you who are newer to the industry to help you remember this stuff, if you're prepping for a test, these will be a very good way for you to kind of catch up on some of the basics before test time. So to end off today's episode, I'm going to play a completely unedited quote from Ronald Reagan, the the Great Communicator that is surprisingly applicable to the HVAC industry, husband and wife. Both working struggling from paycheck to paycheck to raise a family meet a mortgage, pay their taxes and bills, and yet some HVAC repair prices must be decreased.