This video is made possible by generous support from testo and carrier big, thank you to Tesco and carrier for stepping up in support of technician. Education, hey, this is Brian, were with HVAC our school comm, an HVAC podcast, and what I'm going to demonstrate today is why and how to adjust an expansion valve and hopefully help you keep from some of the pitfalls that you can easily get into when diagnosing, and Then finally, deciding to adjust a expansion valve so first off it's an expansion valve some people call it a te V, which is probably a little more correct. Some call it a t, -- xv, but I actually like to call it a CSV or a constant superheat valve. That's just something I made up, don't call it that nobody will know what you're talking about.

But the purpose of an expansion valve is to maintain a constant superheat at the outlet of the evaporator coil. So first thing a TXV needs in order to function properly is it needs refrigerant flow coming in here? That is fully liquid of the proper sub cooling. So we'll show it this way in order to get the tubes out of the way, so it's flowing in this direction, and it needs to be of the proper sub cooling fully liquid a lot of cases. What will happen is some of these expansion valves actually have screens in the inlet.

This one does not, but some do have screens in the inlet and if the liquid coming in hits the screen, the screen restricts it and actually starts to. It actually starts to boil or evaporate before the expansion valve. Then the expansion valve can't do its job, so you have to get a full line of properly sub cooled liquid into the expansion valve for the expansion valve to do its job. Secondly, the expansion valve functions on a pressure drop, so there has to be sufficient pressure coming in, and so, if you have really low ambient conditions where your condenser is running, you know, let's say it's sixty degrees outside and you're running, a split system in cool mode.

You're going to be running low, head pressure, low liquid pressure and that's going to result in your expansion valve not functioning properly because it doesn't have the required pressure drop, so pressure drop is required and a full line of liquid is required or the expansion valve the Function when I say pressure drop is required. What I mean is, is the expansion valve, creates pressure drop, and so, if it doesn't have sufficient pressure on the inlet, it won't be able to work properly. Balance, port expansion valves function better, but still you do need a you need there to be a difference between your liquid line pressure and your evaporator pressure or your target evaporator pressure in order for an expansion valve to work properly and as we know when I say Target evaporator pressure: what that means is we kind of are looking for a range of boiling temperatures that we want to see in our evaporator. If our evaporator temperature gets too low, then we freeze and in freezers that's not a problem because we they need to be below 32 degrees, but in air conditioning and mid temp.

We don't want our evaporators to be consistently below 32 degrees, because frost isn't something that were that we're looking for so we want to target range of evaporator temperature and that is controlled by the pressure so got to have a full line of liquid got to have A differential between a significant differential between the liquid line pressure coming in and our target suction pressure coming out in order for the valve to work properly. Now, once the valve has those things there's a couple other considerations, one consideration is: did somebody get some junk in the valve to begin with, so let's say that somebody installed this expansion valve or they installed the system without flowing nitrogen and carbon flakes got into the Expansion valve body - and yes that can happen, could it be that they didn't install a liquid line, filter dryer and there was actually solid contaminants in the system. Pulling a good vacuum does not remove solid contaminants, so if there's actually dirt in the lines that could get stuck in the expansion valve, if you don't have a liquid line, dryer especially you know, I like to see the liquid line dryer installed as close as possible To the inlet of the expansion valve to help protect it that can cause failures. What else the if the bulb is connected poorly, so, let's say that they didn't use a copper, strap they.

You know this is the proper strap that goes with this bulb, and I see a lot of newbie text. They'll. Take this I'll kind of show you what they do here. They take the copper, strap they wrap it around the line.

So if it's around the line it's around here, they wrap it all the way around and then they just pinch it together and then they strap it and it's real loose. So it's just like this and it's barely kind of flopping around when you're, when you're making the connection to the line you want to make it so it's so you can barely get this, so you can barely get the screw in and so that way, when you Tighten it down it really snugs down on that line, and of course I mean you could overdo it. Obviously, if you want to be Hercules, but you want to get it nice and snug, so you want this, you want this bulb to be contacting the suction line and you want it to be really really snugly on the line. Now, there's also some considerations about position.

If you look at the parker little parker tech tip here, it'll show you that the recommended position is, you know, kind of in this area on the line, but depending on the size of the line that can vary slightly. My experience is that in really really large suction lines, this makes more of a difference than it does on small suction lines, and so, in most cases for the systems that most of us are going to be working on. What's more important is that it's making good contact with the line than it is the exact placement in fact, you'll see some manufacturers that don't place them in these exact placements, but again just follow the manufacturers recommendations about where about where they go when, in doubt, aside From that, if, if let's say the the suction line, because you'll have some you'll have some expansion valves that are mounted outside the cabinet and if this is mounted outside the cabinet. Of course, the the valve needs to be properly insulated, but the suction bulb needs to also be well insulated on the line it never hurts to have the bulb insulated on the line, because you want this bulb to be as close to the temperature of the line.

As possible, and not not so close to the temperature of the air, because obviously the air coming off that evaporator coil could be a significantly different temperature than the temperature of the suction line itself. So the job of the expansion valve is to maintain a constant superheat. Not a constant suction pressure, so one of the most common mistakes is UC Tech's make when they're going to adjust a valve. Is they adjust it in order to attempt to get the suction pressure up and, as you know, a lot of times, an expansion valve is going to result in the low suction pressure, not because of the valve itself, not because of refrigerant charge.

But because the system is running low air flow, when a system runs low air flow, you have less evaporator, you have less air over the evaporator, which means less available heat, which means lower pressure and the expansion valve. What it sees when you have low airflow is. It's seeing low superheat is starting to see the superheat drop and it maintains that equilibrium by maintaining constant superheat, and so it in order to maintain the superheat, starts to drop the amount of pressure that it allows into the evaporator. So it actually starts to close down and restrict the more it restricts the lower the suction pressure drops.

So in those cases the expansion valve is doing its job, it's doing what it's supposed to do, which is maintained, a constant superheat. If you start trying to adjust the expansion valve in order to get your suction pressure up - and you haven't measured your superheat, then that's wrong. That's not how you do that. So first thing: first things: first, the reason why you would adjust an expansion valve is because it's not meeting the target superheat that it's designed for at the outlet of the evaporator coil.

The challenge is, is that when we read superheat, we most often are reading it out of the condenser. So if we have our our probes here, this is the let's get the right ones. So these are test dose mark probes and, if you're measuring outside of the condenser you'll, be measuring your your suction pressure. Using this converted to saturation you'd be using this to measure the actual line temperature you take the difference, meaning your suction line.

Temperature in actuality would be warmer than your saturation and that's what we call superheat. So, let's say you're running you know 20 degrees of superheat outside well. Could it be that you're also running twenty degrees of superheat inside it's possible, but that doesn't necessarily mean that the valve is not doing its job, because the valve the valves job is to maintain the superheat at the outlet of the evaporator coil. Now again, obviously, I'm talking in terms of split systems, because that's what a lot of technicians work on if you're working on a packaged unit or a water source unit or an ice machine or reach-in or something of that nature, then everything's going to be right there And so this isn't as much of a concern, but on a split system.

You have this long length of line where you're measuring the pressure outside. In most cases, I've actually heard instructor say one time well, you need to install a port on the inside on every service. Call it's like, and that's really not realistic. Putting a port in the inside is a good idea on the suction line for the purpose of reading your super heat at the evaporator coil, but it is not necessary.

You just have to take into account the fact that when you're reading your super heat outside, that's not accurate, you need to read it inside, and so you can read your temperature at the outlet of your evaporator, so it comes out of here and then it goes. All the way through the evaporator coil, then you cook this on the suction line right at the outlet of the evaporator coil, and that's where you read the temperature you're still forced to read the pressure outside, but just use some common sense. If it's a fairly short line set, then it's probably not going to be much different. You're not going to have significant pressure drop down that suction line.

If it's an extremely long line set well, then just keep in mind that you may have a little bit of pressure drop from inside to out on that suction line, and so you may want to you know, take that into account, especially if it looks like your Expansion valve is putting out. You know slightly incorrect superheat, just give it a little bit of grace they're, taking into account to the fact of where you're taking the pressure reading all right. So why would you? Why would you change the expansion valve? Well, we actually had a good use case. The other day Joe Shearer, mentioned that he had a rash of units that were coming right off the factory floor of a particular brand that had zero superheat in a condenser in heat mode.

So, coming right out of this expansion valve, he was getting zero superheat and zero. Superheat means that you're actually running liquid into the suction line. So what he did is he wanted to adjust the expansion valve in order to get it up above 5 degrees of superheat manufacturers generally say between 6 & 8. So if you look at the, if you look at the Parker specs here, it mentions it mentions for air conditioning high efficiency, air conditioning six to eight six to twelve r410a six to eight, so six to eight is sort of a good.

If you want to be nice and detailed about your superheat reading, that's what you want to set it into so, let's say you're running a zero superheat. What would you do so? First of all, let's go ahead and get this end off. This is an adjustable expansion valve. You can see that it's got this nut here that actually covers the stem that you can adjust, which adjusts the spring a lot of expansion valve aren't a lot of them are just flat on the bottom.

You can't adjust them. There's nothing you can do, but this one is an adjustable expansion valve. This is actually part of a Parker. Kitt Parker makes this kit that you can use to replace all sorts of valves.

This this particular valve is good from one and a half to three tons and they come with all sorts of different fittings so that you can use it as flare fittings. This is a chat with fitting chat. Lifts fittings have the lead of a little teflon o-ring and they look like that. But it's a nice little kid and it comes with the you know: the strap and the screws and everything you need to get a nice install and replace this.

You can replace a lot of valves with it in a pinch, so first off we're going to take this off. This is a little trickier to do without it being installed because there's nothing to hold it still, but so that that comes off, and now we see our stem here that adjusts our spring. Now, if I tighten this down the easiest way to think of this there's a couple different ways you can think of it, but just remember that the spring pressure is in a force opposed to the bulb pressure. The bulb is an opening force.

The external equalizer is a closing force and the spring is a closing force, along with the external equalizer and those balance out in order to create our superheat. Alright, the first thing to know is that most of these valves come set at 50 percent, so 50 percent stem height, so you'd have just as many turns out as you would in, and so, if I want to decrease the superheat, which means feeding more refrigerant into The evaporator coil, which means a lower superheat, so feeding more refrigerant in the evaporator coil more open of the valve, means fulfilling the evaporator coil with more boiling boiling refrigerant which results in a lower superheat. Then I would open this so I'm using the term open, but I would I would turn it counterclockwise, so lefty loosey, I would open it out and that results in more flow through the valve which results in a lower superheat. If I want to increase my superheat, which is the case that that Joe had mentioned in the heat mode expansion valves that were running zero superheat, I want to get my super heat up to around five or six.

Then what I would do is, I would tighten it down, so it actually makes make turns in the clockwise direction. So turn this way in order to close down the valve more and increase my superheat. That makes sense so a couple important considerations. First off don't start adjusting a valve until the system has run at least 15 minutes more likely, 30.

Okay, so the system has to run your head. Pressure has to be high enough. So if you have, if you're running low ambient conditions, don't start adjusting your valve, don't start adjusting your valve unless you actually read the superheat at the outlet of the evaporator coil, not at the condenser outlet of the evaporator, and confirm that it's either low or high And it needs to be significant. I mean, if you have an expansion valve, that your target is say seven and you're running nine.

I wouldn't a just your superheat on the split system on a very charge. Critical system, like maybe a nice machine, then sure, then, in those cases you can make an adjustment. The other thing is: is that once you make an adjustment to it, you need to let it run a while again in order to settle in so make sure everything else is correct. With the system make sure you have sub cooled liquid coming in make sure that you're, not seeing frost before the valve make sure that your head pressure is high enough all those things and now you're just reading the valve and you're just reading the superheat at the Outlet of the evaporator coil, okay, make sure that everything else is done properly and now you can start adjusting the valve.

So let's say we want to increase the superheat because it's at zero and a heat mode system. So here's what we do. These stems usually turn. They they'll be kind of stuck, but they usually turn pretty easy once you get them unstuck, and so what I suggest is do one half of a turn at a time which is just essentially turning your wrench over once.

So if I want to tighten it down, which is to close down the valve, I just turn the wrench over one time, so I just flip it over that's one half of a turn. Now, I'm going to run the system, I'm going to put the panel's back on I'm going to run it I'm going to check it again and see what I got and then, if I still come to low, then I'm going to turn it over one more time And this is a full turn now now manufacturers of Valve's will tell you different things. This particular valve says make one half a turn. Two one turn per test, but I'm going to tell you just a safe practice.

Just do it turn into time sure it will take a little longer, but you're going to be you're not going to overshoot and also every time you're. Turning this, I don't like adjusting about more than you have to I just like being gentle with it any time you start adjusting stems and things things can go wrong. You see guys start to try to torque down on it and you know whatever. There's there's lots of things that can cause you to have higher lows: super heat that aren't the valve.

So I'm telling you to do it half turn at a time, because it's just a more conservative way of doing it, and so you just every time you make an adjustment. You put everything back together and make sure all your panels are on everything's buttoned up and now you monitor the superheat for another 15 minutes or so and see if it's where you want. It's not you make another adjustment and you just keep doing that until you get it dialed in where you want I've. Seen guys do this where they're they do it with the panels off, and you know they're just making all these quick adjustments check in a couple minutes and redoing it and then moving it back and forth and making all sorts of changes.

Don't do that. I mean an expansion valve is a very sensitive piece of equipment. You know. Obviously we know the the tubes are sensitive, but if you start torquing down on this thing, they're too far open or too far close, it's going to mess up the valve, and now you got to replace a valve and I'm going to tell you a lot of Times when when, when guys go to adjust a valve, sometimes it doesn't adjust, meaning it will adjust slightly but you're not going to hit your targets superheat and that may be, because there's actually something wrong in the valve and the most common things that happened to a Valve honestly are either something foreign gets jammed in it.

It can get stuck. We know of cases where the actual inside mechanism gets stuck, especially in that incident with the rust inhibitor that we had with some some particular types of compressors and then also the actual bulb loses its charge. That also happens. You can see cases where the external equalizer actually gets blocked because of how somebody installed it that happens, but it's much more rare.

More often than not. Either you lost the charge in the bulb which causes the valve to slam straight down. You got some junk in it which causes it to run a high superheat or it's sticking, and when it's sticking it can stick open or close, but generally it sticks closed and you run high superheat. So just adjusting the spring isn't going to fix that.

This is really just a very fine adjustment in order to make small changes in your outlet superheat, but it is a valuable thing to know how to do, especially when you get into more critical systems. Refrigeration ice machines, things of that that very small adjustments can make a hue difference, and it's also just a really good thing to know how to do, and so finally, just to kind of wrap up here, adjusting it down. So what we would call tightening or turning clockwise will result in a higher superheat higher superheat means that it's that it's filling the fabric oil-less full. So it's picking up superheat sooner in the coil means you're feeding less refrigerant into it.

So tightening down or turning clockwise means less refrigerant, being added to the to the evaporator coil and the more that you loosen and I'm saying, tighten or loosen just so that you can think of it. That way in reality, you're just turning it clockwise or counterclockwise. Counterclockwise allows more refrigerant to flow through and when you do it do it one half turn at a time. So just one.

So if you have your wrench this way, it would be turning it until the wrench is this way or just turning it 180 degrees. So just one half of a revolution, so it's basically it just be very careful and do it small increments at a time and and make sure to run the system an adequate amount before you make additional changes. This has been Brian with HVAC our school podcast HVAC. Our school comm HVAC school podcast.

Thank you for watching and we'll see you next time. You.