Hey thanks for watching this series of videos on epa prep, specifically preparing for the epa section 608 exam, which is the exam that every hvacr technician needs to take and pass in order to legally handle refrigerant, whether that's recovery or charging anytime you're going to be taking Refrigerant out of a tank and putting it in a system or taking it out of the system and putting it in a tank, you need to have your 608 license and the 608 license, as we've talked about before, has four different parts, and it breaks down into Three different certifications, so you need to have core and then you've got type 1, which is small appliances, type 2, which is high pressure appliances. But really it's it's most of the types of equipment that we work on and then type 3, which is your very low pressure, appliances or systems, and that would be your chillers specifically centrifugal. Chillers would be the most common application, but really anything that is a low pressure appliance and one again, when i say appliance, i'm really just talking about a piece of equipment, so it doesn't mean a kitchen appliance. It means any sort of piece of equipment, so type 3 is our last part.

It is the part that most technicians struggle with the most, because it's the one that we use the least there is a much smaller section of our industry that works on these low pressure types of appliances, specifically chillers. Historically, that would have been centrifugal chillers that operated on r11 more recently, r123, more recently hcfc r123, which is sort of the r22 of large low pressure chillers and then even more recently, we went to refrigerants such as r514a and then r1233zd is a modern refrigerant, so That would be an hfo which is sort of the next generation of replacement refrigerants that's used in modern low pressure. Chillers a lot of the same things are going to apply to type 3 that apply on core type, 1 and type 2. So make sure you follow those first and like i've said in all of the videos.

This is just sort of a quick refresher, just something to supplement um your study. You need to be trained on it specifically by organizations that do this specifically uh esco is a really great source, mainstream engineering. You can find out more also in rses, and also i didn't mention this in the other ones, but the racked manual, the refrigeration and air conditioning technology manual has a really good section on this. So those are some really good study resources.

I would also encourage you to take some practice exams, maybe use flash cards, there's a lot of good apps that allow you to practice uh the exam as well just so you get used to the sorts of questions that you're gon na get. In many cases. They will not be the exact questions that are on the exam, but they'll often be in the same ballpark and so it'll just help. You prepare for the exam big thing with low pressure appliances that you also have a prohibition on venting a prohibition on allowing that refrigerant from entering the atmosphere.

But one thing: that's very unique about low pressure appliances, which is why it has its own certification. Is that often they hold very large charges because again often they're low pressure, centrifugal children, but another really interesting feature is that in many cases the low pressure side of the system, the evaporator and the entire low pressure side entering the compressor going down that suction line Will be in a vacuum in relationship to atmospheric pressure, and this is because atmospheric pressure is 14.7 psi a at sea level, and so there is pressure on us at all times, and so there is pressure inside of the low side of the system. But it's just lower than atmospheric pressure and so there's still refrigerant present. But if you have a leak on the low side, what will happen? Is it will suck air into the system rather than leaking it out, which makes it very unique in how that works? And so, when you have a low side leak, you're not going to see refrigerant leaking out instead, you'll have air entering in.

You can still have leaks on the high pressure side of the system, so that would be on the outlet side of your compressor, your discharge line, going into your condenser into your liquid line and back that whole section will still be under above atmospheric pressure. So those can leak out, but you have this issue on the low side where, if it leaks, it will draw air in, and so you have something called a purge unit and that purge unit goes on top of the condenser. And if you get air in the system, it will begin to purge that air out. But you will also lose refrigerant in that process, because the refrigerant will be somewhat mixed with the air.

And so you will have some refrigerant loss, and so one of the best ways to prevent refrigerant loss through the purge unit is to make sure you don't have leaks on the low side. So indirectly, you will still result in refrigerant being leaked out, but that happens kind of reverse of what we normally think, rather than the refrigerant being pushed out air sucked in and then you have the loss through the purge unit, which is on the top of the Condenser, let's take a quick look at our levels that we need to recover down to now. The epa calls this evacuating the refrigerant or evacuation levels, but when they're talking about that, they are specifically talking about recovery. What levels of vacuum do you have to pull the system down to and on this low pressure system? If you take a look at the bottom of this chart for systems where you're using recovery equipment that was manufactured before november 15, 1993, you have to evacuate down to a 25 inch vacuum 25 inches of mercury or if it is manufactured after november 15 1993, which Would be the mass vast majority of the equipment we work on, then you would need to evacuate down to either 28.9 inches or what they show generally on.

The charts is 25 millimeters of mercury, absolute, and so i'm not gon na go into the difference between those two pressure scales, but they are the same so 28.9 inches of mercury column is the same as 25 millimeters of mercury, absolute you're kind of going in two Different directions on those scales, but both of those would be the correct answer for a system where the recovery machine was manufactured after november 15. 1993.. Another thing to know is that hcfc-123, which is a really commonly used refrigerant in these types of in this type of equipment, because it's a low pressure refrigerant is a b1 refrigerant. So that's that from that ashrae chart where it talks about a refrigerants, are non-toxic b.

Refrigerants are toxic because 123 is a b refrigerant. That means it is a toxic refrigerant, which means that you have to take some special care. You have to have alarms in any mechanical rooms to make sure that you're monitoring four concentrations of our 123. You have to have mechanical ventilation in those rooms to make sure that if there is a leak that it can automatically be ventilated to the outdoors and then any rupture disks need to vent to the outdoors.

So they need to be piped outside, so that if there is a rupture, then it's not venting all of that refrigerant inside the structure. In addition to that, there needs to be at least one self-contained breathing apparatus for maintenance staff. If you know you need to get in and actually work on the equipment that now has a leak, try to repair it, you need to have self-contained breathing apparatus, so you can get in and do so available to you again, like any other large piece of equipment. If you have more than 50 pounds, you need to keep a log of all refrigerant, that's being charged into that system, so that that way you can ensure that you're not exceeding the allowable leak rate.

So again, the same rules apply depending on the particular purpose of the low pressure system. That would dictate what the allowable leak rates are in a given year and you have to keep a log book in order to ensure that those rules are being complied with and you're, bringing the leak rate down below the acceptable limit. When you are pressure testing, a low pressure device do not use a test pressure over 10 psi, and i know that seems crazy because we are used to uh. You know pressurizing to much higher than that, but you can risk uh blowing the rupture disc on the low side if you pressurize above 10 psi.

So that's the standard test pressure when you are charging a low pressure refrigerant, especially when you have a chiller barrel where water is present, you want to bring the pressure up to above 32 degrees saturation by charging with vapor. So remember this charge with vapor. Until you get above the freeze point of the refrigerant before you start adding liquid, because you don't want to add liquid in below that, so it would potentially freeze the water in the chiller barrel and possibly cause damage to the chiller when you're recovering recover liquid. First, by recovering liquid first, you are kind of doing the inverse you're preventing that boiling process from occurring which can result in freezing and damage to the chiller.

So when you are recovering refrigerant recover liquid first another thing: that's a good practice is to heat the oil. So that way that helps that oil release refrigerant as you're recovering that's a good practice in all of the different segments, especially in low pressure equipment. It's a little more challenging to get the refrigerant out because you don't have as much pressure differential and so any uh heat that you can use again. Do it safely and you're not just taking a torch and putting it on things, but using heat in order to drive the refrigerant out of the oil can definitely help the process.

Also chilling tanks chilling your recovery tank, as we talked about last time. That's another way to help get refrigerant out of the system and into a tank. The term used for the pressure test of chiller tubes is called a hydrostatic tube test, and so, when you're doing a leak check on chiller tubes, you use a hydrostatic tube test to do that. The reason why you have to pull a low pressure appliance down well below atmospheric pressure when you're doing a full recovery, a major repair as the epa dictates.

If you had a heat, exchanger replacement, you're, replacing a compressor or you're replacing you know, condenser, evaporator or anything anything that's large. You have to pull it down below atmospheric is because a 350 ton, r123 chiller at atmospheric pressure can still hold easily hold 100 pounds of refrigerant. So that comes up a lot. The epa talks about that um as a standard.

So the idea that pulling things down to atmospheric has all of the refrigerant out is certainly not true of any system. But it's definitely not true when you're dealing with a low pressure appliance that the evaporator is constantly running under atmospheric pressure. So when the refrigerant in the system is operating at near atmospheric pressure and on the low side below and on the high side, only slightly above, it stands to reason that you have to pull it down well below atmospheric pressure. In order to get that refrigerant out and that's where those standards come from, but just keep in mind when you're doing a minor repair, you can still pull to atmospheric pressure and that's when you're only going to have a small section open so you're replacing you know.

Maybe a pressure switch or a transducer or something very small. In those cases you don't need to pull down to that lower level, but in certain circumstances you may actually have a pressure, that's below atmospheric pressure standing and so sometimes in order to get the pressure up. Because you don't want to open the system and have air rush in and you don't want to have refrigerant come out, you sometimes may need to actually warm the refrigerant in order to get it up to zero psi, and in those cases you can use heating, blankets. Sometimes even heated water from the heating system you can use in order to get that pressure to zero.

In fact, that's a practice that's used for leak detection is you can uh actually warm up the system uh when it's off in order to drive those pressures up in order to perform electronic leak check to get it up? To that point, where you can adequately use a typical electronic leak detector to find leaks, that is one method, that's used and so again use your heat wisely again. Never overheat! You don't want to. Potentially, you know blow a rupture disc, but just enough to get it up so that you can measure a leak so that the refrigerant is moving out of the system versus air moving into the system. Ashtray standard 15-2013 is the standard that talks about refrigerant leakage.

Safety within a structure for all refrigerant types, so everything that relates to um, you know again. Is there going to be a leak, that's so great that it could potentially displace oxygen or is it a toxic gas that could potentially be a toxicity issue, a b refrigerant or is it flammable and now that's a concern? So all of those standards can be found at ashrae standard 15-2013 and specifically applies to these sorts of appliances, because you have r123, which is you know, a toxic refrigerant, very common, and also the fact that they hold so much refrigerant and final little tip is that In cases where you have a sight, glass or refrigerant site glass that is frosted up. I forgot to mention this on some of the others, but in order to clear up that sight glass, you can use a spritz of isopropyl alcohol, don't use a torch or something else silly like that use this spritz of isopropyl alcohol and then wipe it off and Then you can see into the psych class, so that's it. That is low pressure refrigerants again.

Certainly not the whole story. Read your study guide. Do your practice, exams and uh, hopefully you'll be prepared to be a universally certified technician, which is a technician that has core you've passed core and then type one type, two type three. It's a nice resume item.

Some people may say why would i wan na pass type three. I may never work on this type of equipment, and that may be true, but it's a nice resume item and then you just don't have to worry about it anymore, once you're universal certified. So hopefully you found this helpful, as always, you can find out more by going to hvacrschool.com but again follow up with those organizations that give the exam such as esko and mainstream engineering thanks so much for watching we'll catch you on the next video you.