All right, so this class is by special request, and it does feel like one of these topics that we've talked about like a zillion times but comes up all the time, and it is probably the most common joke in the field. Is you have a problem with the system? It's probably bad TXV, let's first establish, why do TX fees get misdiagnosed? Why do people always think that it's the TX fee or how do you? Why is it that the TSV is often the suspect, usual suspect? Do you have any ideas of what that might be carry loads are compression right. That is the most common cause, and so what do you technicians typically do? I shouldn't say: technicians, we'll use that word loosely, but what do a lot of people out in the field commonly do when they see low suction pressure? What's their first response, they grab a tank and they start adding a version to it. Well, on a TXV system, the TXV responds to that by starting to throttle down, and so in a technicians, mind that behavior that the TXV exhibits is a problem, because I'm adding refrigerant my pressures aren't going up.

It must be the TX v, which is actually the exact opposite of reality. The fact that the TX V is throttling down, as you more add more refrigerant, is an indication that the TX v is functioning properly, is doing its job. So this is a THD that we did a cutaway on. It's not very dramatic, there's not a whole lot, this it's hard to do a cutaway on these and actually be able to see anything into it.

But let's talk about the different parts of the TX e. So you have the you, have the bulb and you have the external equalizer. Now there are some valves that are internal eagle-eyes, that don't have an external equalizer but modern air conditioning refrigeration. You generally you're gon na, have an external equalizer easiest way to remember how i TXV works.

I call it a constant superheat valve. You know we have a podcast fact, the first podcast we ever did. We talked about the t. -- xv should be called the CSV.

The constant superheat valve, and so the TX v has what's necessary in order to measure superheat, just in the same way that what you need in order to measure superheat is. You need a gauge to measure the pressure on the suction line and you need a temperature probe to measure the temperature of the suction line. That's how you calculate superheat right with the TX v. It just does that mechanic when I say mechanically the actual action of modulating the superheat is done mechanically inside, but it's doing it through pressures.

So it's directly dealing with pressures, it's not converting it to a temperature and using a PT Charter or a gauge. It's just directly comparing these pressures and by those by those pressures by those mechanical forces it maintains superheat. So it's measuring the temperature of the suction line at the outlet of the evaporator. It's measuring the pressure of the suction line at the outlet of the evaporator, and then it also has a spring pressure which in some cases is adjustable in the case of this valve.

It wasn't adjustable, but you can take the end cap off and you can adjust the stem in order to affect that opening and closing. In this particular case, the spring pressure adds a closing force in addition to the external equalizer. So external equalizer is a closing force. The spring is a closing force and the bulb is an opening force.

You know one of the earliest things we talk about in an air conditioning, refrigeration pressure temperature relationships. You know you increase the temperature of something. You also increase the pressure. You decrease the temperature, something you also decrease.

The pressure right. You have a fixed amount of refrigerant in this bulb, so there's a fixed mass of a refrigerant charge in this bulb, and so, if I heat up this refrigerant, that's in this bulb, then it's going to exert greater force, and since this is the opening force of The expansion valve the bulb pressure is what causes the valve to open the hotter. I get. This bulb the more it's going to drive the valve open, and so that's why a lot of technicians will say you know, pull this off and warm it up with your hand.

You know that's a common thing that they'll that they'll say you know: how do you test it TXV? Oh, I pull the bulb off and I'm warming up with my hand, that's all fine and dandy, but what a lot of text will do is they'll. Go to a job and it's got low suction pressure. We're talking about this very practically! I'm really! I'm gon na try not to go too technical here and just make it like real world. They go to a job.

That's got low, suction pressure, they say. Well, I heard that what I should do is pull the bulb off, so they go and they disconnect the bulb and they warm it up. They go look at their Gage and they might warm it up and run outside real quick. They might put it in a glass warm water, they might even seen some guys heat it up with a torch.

Don't do that, but I've seen guys do that use a heat gun. Stick it outside the cabinet. They do all kinds of things and they go outside and they're suction pressure goes up. Well, what determination do they based on that information, so they did a test, but they did a test, not knowing what the outcome of the test should be with a functioning valve.

Your suction pressure is going to go up slightly under most load circumstances. If you're under really high load - and you know again - you were measuring it wrong or something then that could that could cause problem, but we're assuming that our suction pressure is low. And so you are warming it up in order to drive your suction pressure up and a functioning valve. When you do that, your suction pressure will go up, because what and also your head pressure will also go up a little bit too.

It won't happen instantaneously, but what's happening when you one this bulb up, because this bulb is the opening force. The valve goes open, allows more refrigerant into the evaporator coil, when you more refrigerant in the evaporator coil that refrigerant density in the evaporator coil increases, because you got more of it right. Suction pressure goes up. You have more refrigerant ending back to the compressor.

So now that your head pressure is also gon na go up on the other side, so it kind of creates this. You know increase and pressures all the way around. Generally speaking, now again, if you just do it for a couple seconds, you may not even notice it, but because this is the opening force, that's what should happen now. Let's say it doesn't happen.

Let's say you go and you heat up this bulb and nothing happens, because this is a diagnostic tool at all you guys used to well, it could be that the bulb has lost its charge. That could be because this bulb is the opening force for this valve. It could be that this bulb is no longer exerting that force on this valve and in some cases, these power heads just this top portion here can be replaced by itself without having to replace the entire valve, especially in commercial, refrigeration, large commercial, those sorts of applications. So you want to know the difference, and, generally speaking, you can kind of tell - and I know this sounds sort of weird but a bulb that has no refrigerant in it.

It has kind of a different sound to it. It has a lightness to it. You can kind of tap on it and you can tell that there's no refrigerant in it again. That's a feel thing.

It's really hard to demonstrate. I should probably take two and show the difference good idea for another video, but you can generally tell when it's lost charge. Sometimes you can see the fact that it's lost charge. You can see the fact that there's a crack or something in the end, the line at that point you can't recharge it and I've seen guys, there's all kinds of crazy strategies out there to get TX keys working temporarily.

You know I've seen you guys drill holes into the side of the bulb and put a Schrader in it and try to charge a little refrigerant and I've seen guys do the nitrogen to drive the valve open and for temporary operations. Sometimes you got to do weird things, but in most cases where the charge has leaked out of your bulb, you got a replaceable power or the depending whatever the case may be. That is your opening force. So when you heat it up, you would expect to see it go open a little bit.

The problem is: is that how much should it go open? Well, you don't really know you know so. You're gon na heat it up, and so a lot of guys will see it well. It went up a little bit, but it didn't go up that much still place about. So the point I'm gon na kind of get to is that that test, the wallet doesn't maybe has a little value.

It isn't a very valuable test, not the first thing that I do. I'm not gon na go and grab the bulb and heat it up. That's not the first step I'm going to take so we're gon na get down to how you actually do diagnosis, opening forces the bulb. Closing forces are both the external equalizer and the spring.

If you have bulb pressure, but you don't have the closing pressure, it's gon na go too far open, which can happen in a valve more uncommon, but it can happen and well I shouldn't say more uncommon. There are cases like we work with large grocery store refrigeration, and we set a case and when you set the case, you've got to set the superheat on that valve, and so, in a lot of cases, those evaporator coils may be flooding back because the TX these Are too far open unless you set the superheat we're generally talking about residential air conditioning and we're in the valves are set from the factory for that unit and there's not as very unlikely that you're gon na need to adjust a TX II? And so it's very unlikely that you're gon na need to adjust one, especially for being too far open. That's just not a common thing, that's gon na happen, but it can happen spring external equalizer bulb. The balance of those forces is what causes this to be a constant superheat valve, that's its job.

Okay. So if it's job is to be a constant superheat valve, then our job is to make sure that it can do its job first and foremost. So it's got to have some things in order for it to work properly. The first is, it's got to have a full line of liquid coming in.

It doesn't have a full line of liquid coming in to the valve. Then it's not going to be able to do its job, and so how do we tell if it has a full line of liquid, so cool sub cools that we tell you're working on refrigeration? You may have a sight glass sigh class gives you that same sort of indication, a lot of people wonder in refrigeration. Why you don't measure sub cool as much or why it something as important. You can measure it, but as soon as you have a receiver, that's in the circuit that kind of changes things a little bit.

So in most cases, refrigeration technicians are clearing a sight glass. That's how they're thinking of it but saying clearing the sight, glass and saying having a proper sub cool. Those are kind of the same thing in the same category. The idea is that this is the metering device.

Its job is to create a proper pressure drop and a proper feed of refrigerant into that of a protocol, and it has to have a full line of liquid coming in. Do you ever go up to the unit, that's making the chase and that's an indication that you have some vapor in that liquid line? It doesn't matter what your sub cool is outside. If you hear that coming into your valve, you still have vapor in your liquid line, and that can happen because of restrictions. You know restricted dryers.

It can happen because of long line length at high temperature. Anything that can cause that refrigerant in the liquid line to lose its subcooling to start to become vapor again pressure temperature in a line length. All those things are impacts on that, and so, if you're not feeding your expansion valve with a full line of liquid, that can cause it not to do its job. And I'm just saying this because it's two different categories of misdiagnosis on TXV, the one category is a complete misunderstanding of how it works and that's the whole.

Well, my suction pressure is also I replaced it. There's no reason for that. One, the other one, which is a little more tricky, is that let's say this: has a some valves have this. This one doesn't, but let's say it has a inlet screen and so that inlet screen is actually where the restriction is and not the body of the valve, the body of the valve inside here, the actual seat, where the refrigerant goes through.

That's supposed to be a restriction, it's designed to be it's a pressure drop device that maintains constant superheat, but let's say there's a little restriction here. If this restriction here is not allowing the correct amount of refrigerant to actually hit the valve, then the valve may be doing its job and the problem may be in that Inlet screen, and so we've got to do everything to make sure that this valve is getting The proper amount of liquid refrigerant coming in it also has to have a proper pressure drop. Now we live in Florida in Florida. We, you know, we run air conditioning most of time when it's pretty hot outside, and so we don't have a big problem with this and residential.

But there are cases where you may be running air conditioning and it may not be very hot outside, and this especially comes up in refrigeration in refrigeration. You could be running, you know, freezers inside of a grocery store and it could be. You know negative 20 degrees outside and you still need to run those freezers, and so when we are exchanging heat to the outside air, that's where we exchange our heat to in our condensers and that outside air then has a lot of control over what our pressure. It, and so, unless we can keep that pressure up high enough about generally speaking in this varies, but about 100 psi higher than your desired evaporator pressure, then your TXV will also lose control.

You need to have about 100 psi pressure drop again in most cases. That does vary and with electronic expansion valves they have a little more control even but you need about 100 psi differential and so the where that comes in. Why that matters is when your outdoor ambient conditions drop or, let's say you're, using water and a water cooled condenser. If your water temperature got too low, for example, or your flow rates are too high, where you didn't have high enough head pressure, then that could cause your TXV to lose control.

You have to have a full line of liquid. Your head pressure has to be high enough now that head pressure high being high enough thing that that doesn't come up a lot with what we do in residential. Because, again, if you're running air conditioning in most cases, it's hot outside, that's why we run an air conditioning so that shouldn't be a problem. But in certain cases that can come up and commercial that can come up.

You could have a space where you're running air conditioning it could be 50 degrees outside the general rule is for typical air conditioning with no specialty controls. You really can't run air conditioning when it gets below 65 degrees outside it's a typical residential air conditioning with stuff. We work on everyday if it gets below 65, then you're gon na start losing control over that difference between your evaporator pressure and your liquid line pressure, the pressure coming out of your condenser. So here's where the rubber meets the road section pressure is low and they don't know what to do about it.

When that happens now, we've already determined suction pressures low. The next thing that technicians should do measure superheat and sub cool inside and outside practically speaking on a residential split system. What that means is, as you take your sub cool and superheat outside, but you pay attention to what your line temperatures are outside. I measure my superheat outside we'll say it's 10 degrees, so superheat, okay and my suction line temperature is will say: 50 degrees, 50.

Minus 10 is 40. That means my suction saturation is 40 degrees. Okay, so because 40 plus 10 degrees of superheat equals that suction line temperature of 50 sub cool outside and a liquid line, temp of 95 degrees. That means that our saturation is 105.

These are pretty typical types of numbers that you'd see in a runner mild summer day. This is my outside. This is what I've got outside, so I've got a 95 degree liquid line outside 50 of you resection line outside now I go inside and my suction line. Temperature is 47 degrees, and my liquid line temperature inside is will say it's 93 degrees, so the temperature of the suction line increased from inside out by 3 degrees and it dropped from 95 to 93 traveling inside okay, that's very realistic for our environment.

We run these copper lines in chases, underneath buildings, and you know there you're on the liquid line in the section lining together. Even when you insulate them. Sometimes it gets water and there's so there's a little bit of heat transfer. Now I would rather see these two numbers be the same.

I would rather see these two numbers be the same. That would be my preference, but realistically that's not always gon na be the case. This is an indication if I were to see this under normal circumstances. This would not be an indication of a problem I wouldn't think to myself.

Oh my gosh. I've got a restriction. You know, I've got a line. Dryer I've got a kink liquid line or something I've got something weird going on.

This would be about what I would expect to say, because it started off at 47 degrees inside, which means that now my inside super heat is seven degrees. My inside sub cool is 12 degrees. Now it went that way versus the other way. Now that's tricky because I don't know what the pressure is inside and so that temperature could have dropped just because it gave off a little more heat inside the chase or that temperature could have dropped because there's a kink or something.

And now my pressure dropped and that would mean that the sub cool that I'm assuming is incorrect because again I'm measuring my pressure outside and I'm measuring my temperatures inside. So that could be a problem and that's why I'm still listening when I go inside and I listen to that liquid line, I'm listening to here. Is it or am i hearing that sound because again it would be beautiful without a port, then I could just check my superheat and sub cool inside as well, but I don't have a port, so I have to kind of just go off of what my pressures Are outside so there's always the possibility for a kink or something not very common and generally, if you have a line dryer, you can just measure the temperature across the line. Dryer, that's another common cause.

Technicians will miss diagnose, TX fees, because if restricted line, dryers restricted, Inlet screens and then because of air flow, which is what we're gon na talk about now. So I checked this: that's all! Okay! Now, let's say that I run into because this is. This is a pretty typical circumstance here, but let's I run into something that's a little bit more insidious to r410a. Let's go with what we would consider to be a low suction pressure, because again this is the first indication that a technician would have that.

Oh, I think, something's wrong. Okay, let's say we run into a system and the section pressure is 105 psi. 105 PS IG so make sure that you're on the gauge scale on that app thirty-three point six degrees and we call that suction saturation. My preferred term, for it would be evaporator temperature, so we have a thirty three point: six degree of operator temperature, that's the temperature of the boiling refrigerant inside the evaporator, that's lower.

So let's say that the inside temperature is inside. Temp is seventy five degrees. We should see in general under most circumstances, 400 CFM per ton, type of circumstance about a thirty five degree difference between the indoor temperature and the section saturation otherwise known as the evaporator temperature. You can see we have more than that.

Seventy-Five minus thirty five is forty. So we're six point four degrees low from what we think that we should be. While this isn't way out of bounds, it's definitely low suction pressure. A technician who's been around long enough to hook a hook gauges, do a couple things.

It's gon na say my suction pressure seems low, and this is where things start to spin out of control. As far as the TX V goes, it's close to freezing right. So that's a good indication. That's a good thing to have thought and I even get a more junior tech.

They may not even perceive that they're close to freezing, but at least you get to the point. It's like. Alright, that's close to freezing! That's, not good, okay! So now what is the next step that I take? Most technicians are gon na go and I shouldn't say most, but a lot are gon na go and they're gon na go for their tank, they're gon na say it's low, they're gon na quote the customer or whatever I got low suction pressure. That is not the next step.

The next step is to go ahead and get the rest of your the five pillars that we talked about. Superheat sub cool air temperature split section pressure head pressure. Those are the the standard ones that we that we do and there's a lot more than that even but we're gon na start with that, so my suction pressure is low. The first thing I'm gon na do is check my super 8 in sub cool outside.

So let's say my sub cool outside is 12 degrees and my superheat is 14 degrees outside. So a lot of technicians are gon na. Look at that you're gon na say. Well, you know.

Fourteen superheat, I mean that's, that's not real high, but it's a little high. Maybe I have a bad TX v TX C's job is a Const superheat valve, maybe have a bad TXV, so they're gon na get that seed of thought in their mind. I can tell you this is not about TXV. This is not a bad TXV.

If it was a bad TXV, meaning failed closed cuz, that's what we're saying Tex also get failed, closed and failed, opened. Confused, failed closed means underfeeding, it's not allowing enough refrigerant into the coil. That's what we're looking for here, because we are saying that we have low suction pressure. Low suction pressure means that if it was the expansion valve, it would mean that the expansion valve wasn't feeding enough refrigerant into that of a per to quo 14 degrees.

Superheat is an indication that it is not under feeding significantly at all. It would be definitely higher than that because again, where did we measure this? We measured it outside. That's where we always measure it first, because where we hooker gauge is up so now I go inside and I remesh my superheat, and I see that inside I have a 10 degree supreme. This would be very typical.

It's heads a chance, as its run from inside, to outputs to pick up a little bit more superheat in that Chase or whatever the case may be. You mean it depends. Obviously, if you've got a line set, that's you know four feet long. Then that's you're, not gon na see a big change.

You shouldn't see a big change, but if you get a line set, that's running through an attic or it's going through a chase and it's 50 feet. You're gon na definitely see some change in temperature. So now inside we have a 10 degree superheat. Well, that's right! Where we want to see it.

What I generally say in residential air conditioning is 6 to 14 degrees of superheat at the evaporator coil. That's about what you're looking for now again, if you test you know 50 of them, more of them are gon na, be in them in that middle range, more, like 8 to 12, that's gon na be, but you know sometimes there's a little bit of variation, and I don't want technicians condemning expansion valves over a couple degrees of superheat, because the truth is your tools generally aren't even accurate enough for you to be sure within a couple degree range. You know you could be reading, you can be reading 10 and it could be eight or it could be twelve easily, even with the good quality tools really use, let alone some of the tools that some people are using, because superheat is a comparison of two numbers. Both of those numbers have a range.

That means that you can be a little off one way or the other we're just looking at this situation right here inside temperature, 75 degrees, 105 degree, 100, 105, psi which equals a thirty three point, six degree wrapper to coil. My sub cools 12. My super heats 14. There's other things that I need to check here.

You know I need to actually show you the head sure and split and all that stuff, but I can pretty much tell you right now. I got an airflow problem. How do I know that, because my suction pressure's low I'm eating my evaporator temperatures low and my superheat is in range: it's not high. Now, let's look at this same circumstance, and now we change this outdoor superheat, number 227 Aries and I recheck it inside and it's 23 degrees.

Now a couple more things they got to check. I got to check that whole Inlet screen thing make sure that couldn't be it. I got to make sure that I have this sub cool not just outside, but inside. I've got to make sure all that stuff, but once that's all checked - and I know that I have enough pressure coming in so I got that hundred and Pete hundred psi Headroom between evaporator and the inlet I've got sub cool coming in now I can condemn the Txv because TXV starts at the inlet of that of a protocol and it's tied into the outlet of that evaporator coil, that's what is controlling, and so, if I'm measuring superheat at the outlet of that of a protocol and it's high, which, from a practical standpoint, means That I'm measuring a high suction temperature in relationship to the pressured evaporator temperature right pressure, converted to an evaporator temperature on the suction side.

If that, if that is high, that difference is high, then that means that the metering device, the txp in this case, is under feeding. It's not feeding enough refrigerant through that evaporator coil. If it was correct, meaning it's in that range of 8 to 14 or 6 to 14, that we talked about in residential air conditioning now again the refrigeration guys always freaked out on me, because it's like oh it's different or for sure I get that there are Some you can run very low super heats, you know four degrees, super heats three degrees super heats in some cases, even on ice machines, or things like that, but air conditioning we're really going to be more than that eight to twelve in most cases, but that's at The outlet of the evaporator coil we've confirmed that we've confirmed that we have what we need going in now. We can condemn that TXV when guys misdiagnosed, TX fees and because, in a lot of cases they'll say I checked the superheat.

Well, maybe you checked it outside. Maybe you didn't recheck it inside. Maybe you didn't let it run long enough and so your superheat, I didn't, have a chance to settle in because you were being impatient with it. You see, you saw a high superheat, but you only let the system run five minutes.

Superheat takes a while because it has to go that refrigerant has to go all the way through the circuit, and it has to cool down all of that mass all the thermal mass of the evaporator coil and then all the thermal mass of the suction line. For you to actually measure that superheat, so you got to have let it run for a while. The other reason that a lot of times guys will condemn it Exe when they shouldn't is you know they? My server heat was my superheat was in range. Well, they're tools aren't measuring properly, so that's another reason commonly, but their gauge is reading low.

They didn't calibrate it, they didn't zero it out to atmosphere. I mean even test. Oh 550, s, which are my favorite set of manifolds. You have to zero them out.

You have to open them in atmosphere, hit that zero out button. So that way they reset and you got to do that every time. Otherwise, you could be significantly off on your pressures because it recalibrates you know, and it will it will recalibrate with pressure under it, and it can be really wrong same thing with analog gauges. Obviously, with analog gauges, you could be four or five degrees off very easily, and so you thought that you had fourteen or he thought so.

You thought you had nineteen and you actually at fourteen you're like well. Nineteen is high, but you didn't actually have nineteen you at 14 and 14 is acceptable. You understand this is where guys, who are even good technicians, misdiagnosed expansion, valves, even understanding that it's a constant superheat valve 27 degrees, superheat and 14 degree superheat. That may seem like a big range, but that's only thirteen degrees difference and that's the difference between a failed TXV and a good TXV.

The main thing to know about at exp, though, is it's a constant superheat valve and its job is to feed the proper amount of refrigerant into that evaporator coil, and the way that it knows the proper amount of refrigerant to feed into that of a protocol is Based on the superheat at the outlet of that evaporator coil bulb is the opening force. External equalizer is the closing force, just like Jessie mentioned. Why do you need to pull that bulb up off and warm it up? Well, if you're measuring, superheat and sub cool accurately, I don't really see a reason. The only reason that I can see is that, once you have already diagnosed a valve as being failed closed, meaning it's not feeding enough refrigerant through you can do with a goal exercising the valve, which is just a matter of driving it open, letting it close driving It open letting it close and sometimes that live varnish or whatever is built up in there.

Whatever Gunks gotten in there can freakin free up, we work in a heat pump market, which means you know, pry a t percent of the equipment we work on a residential or heat pumps in a heat pump market. You don't need to do that. Just run it back and forth and heat cool, because that's gon na do a much more effective job at exercising that valve than heating it up with your hand. So that's how you exercise the valve in a heat pump market now either way doesn't necessarily solve the problem.

You got it open baby. I mean I've done that a couple times where I've gotten a valve to free up and now now it's working properly. But did you really fix the problem? In those cases, I'm probably still gon na recommend replacing that valve and then definitely changing out the line dryer, because my concern is what got into that valve the answer byproducts of moisture. You know, so you can get some.

You know all sorts of acids and crap from moisture, because the proper evacuation wasn't pulled and then also carbon if they didn't flow, nitrogen well, brazing that can get in there there's a lot of things. There's the whole issue with the oil additive thing. That happened. A few years ago, where the corrosion inhibitors got in and messed up valve, so there's a lot of things valves are very sensitive than one of the more sensitive components on the system, because the job that they have to do is very fine, and it's it's very.

It's a very detailed job that it has to do. Having said that, TX fees do fail, so the joke that, like oh, it's never that takes me. It's actually always airflow and I know a lot of TX T's. Do they do fail now? Why do they fail? There's a range of different reasons: rub outs on the bulbs and you know vibration and all that, and we see certain brands that definitely fail more than others.

You know we every every winter, on Lennox heat pumps, we go through all of these heat mode, expansion valves and it's just the way that they're installed makes it makes them more prone to fail. On the external side, things that we allowing the system moisture carbon, those sorts of things dirt, because you Lane Tran line set and some dirt got in it or whatever. Those are obviously gon na - have the tendency to get in valves and plug them up. So we want to find the cause as much as possible, but that's the only one who talked about exercising the valve.

That's the only case that I can see actually pulling a bulb off and doing that is on a straight cool system, where I'm wanting to try to exercise that valve. I'm wanting to try to maybe get it open or maybe to try to temporarily get somebody some air conditioning. You know if I can take the bulb out and stick it outside the cabinet a little bit to drive up the suction pressure, get it out of that freezing range again. That only applies if you're super heat is high.

If you're super heat is low, you don't want to drive the valve open driving a valve open when super heat is low, is going to flood back to your compressor. You don't want liquid refrigerant going back to your compressor, and so, if you have low superheat, you do not want your valve to open more. If you have a low superheat, you do not add more charge. This is a just a quick, real talk, absolute statement.

If you have a low superheat, do not add more. That does not solve anything, because what that low superheat is telling you is that your evaporator coil is already fully fed adding more refrigerant to it is not going to fix any problems. It's only gon na make problems worse and a lot of guys are constantly saying well, but I had to get it out of the freezing zone. It depends geographically, but overall the whole range most cases are freezing or caused by airflow.

That's more common cost, dirty air filters improperly sized ductwork somebody jamming a filter inside of a returned grill somebody's shutting off a whole bunch of vents inside the house, because their kids went to college, whatever anything that reduces system airflow below that desired system. Airflow. Really any time you're getting below 300 cubic 350 cubic feet of air per ton on a regular basis, you're gon na run the risk of freezing. That's what you want to look at first, when you're talking about low suction pressure, if it's accompanied by normal or low superheat, not adding charge, it should be very rare circumstance that you're adding charge in order to see what happens, because you already know what happens happening Based on superheat so cool all that the one exception to that is, when you really do have a restriction, when you really do have a bad restriction, sometimes it can be tough to find now, in most cases we know the common areas that restrictions happen, check, valves, Metering devices, solenoid valves, filter, dryer, so those sorts of thing, that's where you're looking.

But when you do get a real bad restriction, then some weird things occur in the system because, like you know - and this is a total aside - but I want to just mention this here, because this comes up. Sometimes, if you do have a restriction, guys expect your head pressure to go up. That's what they they imagine, because they imagine this compressor as a pump, that's pushing against restriction and the head pressure going up on the one side and it dropping on the other. But refrigerant is very dynamic and it changes state between liquid and vapor, and so, if that theory were true, this is just the easiest way to remember this.

If the theory were true that a restriction caused high head pressure, what would happen every time you try to pump down a system close off the liquid line right first and it pumps everything into the condenser? Well, closing off the liquid line is a hundred percent restriction. So if you did that, and that causes a really high head pressure - oh my goodness, you would probably you should blow your convert. Air condenser sky-high right, but that's not what happens. What happens is.

Is that as it gets packed into that condenser and the heat keeps getting rejected off of it, it just turns into liquid as long as you don't overfill it. Now you get to a place where you get to a hundred percent full of liquid. When I you hydrostatic pressure and yes, you will explode it and we see that in some cases with microchannel coils, because they don't have as much volume inside of them, but in a traditional unit we're pumping them down all the time right, no problem, your head pressures, Not going sky-high and that's because there's enough space and that condenser to hold all your refrigerant, you know how you know, because it gets shipped to you with all the refrigerant in it. So we know that it's designed at cold all that refrigerant.

The reason that your head pressure goes up is because heat is being transferred and rejected, because you actually have heat coming down your suction line, that's ending up in your condenser and now that's what's driving your head pressure up. So when you have a big restriction, this is the point: have a big restriction. Your head pressure will actually go down when you have a TXV, that's throttling back or is or is under feeding the evaporator coil. Your head pressure is actually going to go down, and that throws some people off because they will walk up to it and what do they see low suction pressure, low head pressure, I'm low on charge right? That's what they think and that's why you can't just walk up to a system: low, suction pressure, low head pressure, I'm low on charge within reason, an experienced technician.

Can you walk up to that system? It's an art, 410, a system you hook up to it. Oh, I got sixty suction and 150 head okay you're low on charge. Right, I mean so there's a range to all this stuff, but when you see a circumstance like this, oh my suction is a little low, and this is where it always happens. It's a little low ma'am, I'm gon na add a little charge for you right.

That's where no! You got a check, your superheat sub cool. You got ta, let it run long enough before you can make that determination. Hopefully we don't miss, diagnose two things. I forgot to mention in the class one is: whenever you have a low super easy, so you're operating the system, it's run for a while, and you notice that you have a low superheat.

One thing you should watch for is how well this bulb is connected to the suction line. If this bulb is not well connected, it should be connected generally with like a brass or copper, strap very snug on the line position can matter in really large lines. In general, residential, like commercial, maybe small, refrigeration applications, it doesn't matter so much where the bulb is positioned on the line. So well, as it's really well strapped to the line, and then you need to make sure that it's insulated in most cases now some manufacturers don't insulate them in general, not insulating is going to result in a slightly lower superheat.

So if that's, if you're in a range, where that's a problem, then you may reinsulate, I recently insulated a factory bulb on a TXV and it increased the superheat by about three degrees. So it does make a difference, and that is something if you're running too low a super heat that you might want to look at another thing to watch out, for when you have a valve, that's not metering properly is whether or not it has one of these Quarter-Inch flare connections at the inside to use a quarter-inch flare connection - that's fine, but just recognize that most of these don't have core depressors in them. So when there's no core depressor inside this flare, you can't have a core in that port. So you have to make sure that core is out of the port.

Otherwise you won't feed through pressure, and you won't have that appropriate. Closing force like you're supposed to have from that external equalizer.