Uh, let's talk about nitrogen 78 of our atmosphere is made up of nitrogen, and only around 21 is oxygen. Did you know that fun fact um so most of the air when it gets in the system, is in fact nitrogen. So, what's the problem with nitrogen getting inside the system, nitrogen is not combustible, otherwise the entire atmosphere would be explosive. Nitrous oxide, yes, nitrogen! No, what did you say matthew? It's it well, inert means non-reactive.

So that also means that it doesn't react with other molecules um to create chemical reactions, so say that again displaces oxygen, um yeah inside a system, though we don't we don't mind that um. What else? Why don't we want nitrogen inside of an air conditioning system? What do we call that there's a term for that non-condensable, sorry, non-condensable, so why? Why is it called a non-condensable gas because it doesn't condense now? Can it condense? Yes, it can it yeah, it can, and we know it can, because there's such a thing as liquid nitrogen, if it couldn't condense, there'd, be no such thing as liquid nitrogen. But when we say it's non-condensable we mean it does not condense. Inside of the air conditioning system, under normal conditions, be pretty abnormal conditions to get nitrogen to condense inside of an air conditioning system.

So when you have a non-condensable gas inside the system, what does that result in like what happens inside the system when there's a non-condensable gas? What's that pockets of nitrogen okay, i mean to one degree that is true: those pockets tend to occur at the top um. It kind of it kind of floats to the top of the condenser specifically, but really what it does, what the nitrogen does is it just takes up space and when it takes up space it increases your head pressure, makes the system not operate properly. It doesn't really circulate through the system. It does generally just find its way to the top of kind of the high point in the condenser and just sort of sits there.

Doesn't condense just takes up space so, generally speaking, when you have non-condensables you're going to see generally high head pressure, that's the most common thing, but it is also going to affect your pt relationship, which is going to kind of screw some things up as well. We don't want nitrogen inside the system, but we do that. Isn't really what i want to talk about. I want to talk about how we do use nitrogen and why we use nitrogen so first off, why do we use nitrogen to pressure test the system? Why don't we use something else? It's cheap! That's! That's! Probably the number one reason it's cheap and why is it cheap because 79 of the air is nitrogen right? So it's all over the place.

It's easy to get nitrogen. Now we call it dry. Nitrogen. Have you ever heard anybody say that dry, nitrogen ever heard that term dry nitrogen? Well, why do they call it dry, nitrogen? This ain't wet it's because there's no! There should be minimal water vapor in the nitrogen.

Why do we want minimal water vapor in the substance that we're using to pressure test the system we have to vacuum it down afterwards, copper corrosion? We don't want water and water vapor inside the system or liquid water. We don't want any kind of water inside the system. Water creates corrosion water reacts, water is very reactive. Water is a universal solvent pretty much so it creates all kinds of problems inside the system that we don't want, especially nowadays anybody know what kind of oil we use in most of our systems.

Actually there's two types of oil that we use: poe. Does anyone know what the other one is mineral nope? We don't use mineral anymore, yeah you're too busy. Looking at your phone, i wasn't. I was talking about.

Okay, that's just as bad uh, canola oil, no, not canola oil, not castrol, gtx, not mobil, one uh! No! The pve polyvinyl ether uh is used in a lot of ductless systems nowadays and uh very similar to poe, but pve uh pve is actually even more uh. My base, my understanding even more hygroscopic than poe, meaning it likes moisture, but the good news with pve is it doesn't change into an acid via hydrolysis. So when you take poe oil, the oil that we use in our typical 10a systems nowadays and you allow moisture to get into it, not only does it like the moisture and it sucks it up, but then it changes so once it changes, you don't change it Back if you take poe and you contaminate it with water, and then you get the water back out, what you're left with is not poe anymore. You have alcohols and acids that are left over that end up destroying the system over time, which is why, when an old timer will tell you man back in my day, i didn't used to pull vacuum.

We didn't have a micron gauge. We didn't care about any stuff well back when it was mineral oil. It wasn't nearly as big of a deal because mineral oil yeah moisture would get in there and it wasn't good for the system, but the mineral oil first of all didn't grab the moisture the way poe did so. It was easier to dry the system out and, secondly, the mineral oil didn't change via hydrolysis and become this toxic goo.

If you've ever heard, people talk about the importance of changing copper, they would you know you got to change copper. Every time you change system got ta change, copper because those oils they don't mix. You know you hear you used to hear that when we first went from r22 to r410a about how the oils didn't mix and how, if you left that old line set and you put the new refrigerant in there, it was just going to cause all kinds of Problems and some people would say well yeah, you know the new copper is designed for the higher pressures. So let's dispel some myths here, poe oil and mineral oil.

They actually are okay together. Now, it's not great to have a lot of leftover mineral oil in the system, because we don't want mineral oil in with our new r410a systems, because r410a doesn't move mineral oil. That's why we had to change the mineral gets stuck in pockets and coats. The tubing and it creates problems.

So that's why we don't want it, but does the poe oil and the mineral get together and create a toxic goo? The answer is no, it does not. All you have to do is take the two dump them together. Stir them up see what happens? Nothing happens. They just they don't really mix very well, but it's not like a it's, not a major problem.

The problem is, is that we had these old systems that had moisture in them and moisture was in the lines and everything else, and then we put poe oil in it and then the toxic goo is created. So you say: look we got all this black oil coming out of here. It must be because there was mineral oil left in the system incorrect. It was because there was moisture left in the system that makes sense so prior generations, not paying attention to evacuation, have resulted in issues even today.

So what do we do when we go back to a system to install or we go and to install a new system? We do we do a flush on the lines so we're using and we should be using uh the either the pipe wiper kit or the new hillmore kit to push the pigs through to make sure that we get all that stuff out of there right so you're. Physically, getting that old, contaminated oil out we're doing a nitrogen purge to displace the air, then we're flowing nitrogen. While we braze, then we're pulling a deep vacuum right. If we do those steps, copper's, copper as long as it's not damaged, and there ain't no difference between modern, copper and old copper.

In fact, if anything, i'd probably choose the old copper over modern copper, there isn't an issue with copper as long as it's not damaged, and why and can it get damaged sure it could it could get damaged from the inside because it had so much moisture that It was actually being eaten up from the inside; it could have uh. Generally speaking, it has corrosion from the outside or abrasion from the outside. If the copper wasn't run properly, we see most commonly corrosion in our line sets in florida when they're running it through the ground and they use reclaimed water and the irrigation and that reclaimed. Water has really high levels of chlorine and other chemicals to treat it and that eats up the copper.

The other time we see it is when people have water softening equipment, so something to watch for if you're ever going to be quoting a system or you're going back to an install. If you see a water softener right by it and it's dumping on that chase and now the copper is all green and nasty looking and it wasn't quoted to replace the copper go ahead and replace the copper, because, even if it's not leaking now, it's going to Leak - those are just some just some things to know about kind of the old oils and all that, but but nowadays nitrogen is more important than it ever was. We know that we pressure test with nitrogen. Sometimes the question comes up.

Well, what do we pressure test? Two and the answer is the highest safe pressure. There are some challenges that we face if you've ever and i talk about this a lot when you pressurize a system, and you put your nitrogen in the low side right and you watch your high side going up and they're going up together right and then all Of a sudden, you hit a point and it stops going up on the other side of the system. Right so sorry, i said putting it in the low side, i said opposite put it in the high side and you watch the low side go up and then all of a sudden it hits a point where the high side keeps going up and the low side Pegs anybody ever seen that before, when you're adding pressure to a system, does anybody know why that happens? What's that the txv yeah, because the txv, if you remember that external equalizer is the closing force for the valve and that external equalizer, all it is - is just a pressure tap into the end of the evaporator coil into the suction line. Basically, and so as that suction line pressure keeps increasing, that valve is closing, closing closing closing once it gets to a point it slams shut.

That's the very nature of a hard shut off txv. If you ever hear that a non bleed or hard shut off txv and all of our modern valves that we work on in air conditioning are hard shut off, txts going over, that level makes it kind of tricky to do a leak detection. You have to equalize the pressure through your gauges, and that makes it a little less accurate. So, generally speaking, you know bring it right up to that level and not beyond that is kind of a good test pressure other than that.

Just look at the test pressure for both the air handler and the condenser and use don't go over the highest test pressure for whatever the lowest one is so if it's 300 psi or whatever it is. Don't go over that for your test pressure and nitrogen, but the higher the pressure, the more likely you are going to be to find leaks, make sense. Next thing we already talked about this last week, always use soap bubbles. Don't just rely on a pressure drop test because we get impatient with our pressure drop tests.

Just because you don't see a one psi drop doesn't mean there isn't a leak. There could be a leak, then it only dropped to tenth of a psi. In the 20 minutes that you're doing a standing pressure test, which is also why i suggest using digital, either probes or gauges and doing the delta p uh pressure test test on them. In most of your, you know, like your field piece app or your testo app are going to have that in it or the actual gauges, where you can actually set it into delta p mode pressure, drop mode and it'll show you over how much time has elapsed And if there has been a decrease in pressure, so that's always something to always something to look for in order to be more detailed and then do your bubble test.

So that's basic nitrogen pressurization, but there's two other things and you need to know the difference. One is what we call a purge or a sweep, and the other is a flow. So, just because you pressure test and just because you flow nitrogen, doesn't mean you've purged or swept the system so specifically before you start to braze in your lines, it's a good idea to pressurize the lines flow, a good amount at a fairly high velocity, so run A good amount of nitrogen through in order to displace all the air from the inside before you begin to brace in the first place, because when you're flowing nitrogen anybody know what what rate you flow nitrogen at it's, not it's actually not a pressure at all. It's three to five or two to five scfh, which is standard cubic feet per hour.

Tiny tiny flow! What's funny you don't, but but you you can measure it with a i mean, so you can measure it with the old ball floating yeah, the floaters or the whiskey, the whisperer, which is what i uh, and i do i i say the whisper is fine. You know if you, if you just set the t-handle, just get it to where you can just barely hear it barely hear it. That's that's fine, it's you know again. It might be a little much.

It might be a little much, but you just want to make sure that it's just barely barely barely flowing. But again, if you just go straight to the barely barely flowing, you didn't get all of the air out already you want to get the air out then go to barely flowing right and then even once again, it's not a bad idea. Once you get done before you're, actually gon na, do your pressure test to go ahead and purge some more through, especially when you're working on a system that already had refrigerant in it? Okay. So if you're a service tech - and you just did an evaporator coil or you just - did some sort of other repair, it's a good idea to flow nitrogen through the system.

Now a lot of people will say: well how do you flow nitrogen through a compressor, and the answer is that in most cases you do not flow nitrogen through a compressor, but you can flow it through the components around the compressor to get as much of that Air out of it as you possibly can, and then you can also it when in doubt, if you can't flow through it, you can pressurize it and then release it now, jim talks about how that could potentially condense some moisture, that's a whole other topic that we Don't see completely eye to eye on, but you want to create some turbulence in the system in order to help release that refrigerant from the uh from the inside of the system. Anything that's entrained in the oil and also potentially some moisture that gets entrained just helps kind of move stuff around, because especially an existing system when you're using an existing line set, for example - and you didn't do the pigs run the pigs through it that oil in There kind of has these little pockets and it'll kind of be laying in there and so just blasting, some nitrogen through it helps kind of mix it all up, stir it all up and get the refrigerant out of the oil. So when you have a hard time pulling a vacuum, those of you who do things like compressors and evaporator coils you're, going to notice those vacuums don't go as fast as a new system. Anybody notice that they'll stall on you it just it's more challenging generally than a brand new system, and that's where doing that flowing of nitrogen.

We call it sweeping of nitrogen, where i said flowing flowing to new braze, that purging or that sweeping of nitrogen is really helpful, because it helps just kind of get everything moving inside the system and helps that vacuum go quicker same thing. When you have a system that stalls where you're pulling a vacuum, you know your vacuum pump's pulling down properly because you tested it with the micro engage. You know you have clean oil. You've done all that already, but it's still just stalling on you.

That's when you stop, you break it with nitrogen. You, you flow some nitrogen through it just create some turbulence and then go back to pulling your vacuum again and that'll speed up the process. It'll help you get through that stall, nitrogen inert gas abundant in the atmosphere. We don't want to leave it in the system because it takes up space results in high head pressure can also result in some in some fluctuations in our pressures.

So we don't want to leave it in the system, but in terms of things to leave in the system, it's much better than our two biggest enemies, which are water and oxygen. Water and oxygen are the two really bad things we do not want to leave inside. The system, so nitrogen helps us deal with that, and, ultimately vacuum is what makes sure that we're that we're dry at the end, 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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