Good morning Everybody morning! today! We're going to talk about compression ratio and specifically get into some practical, uh, troubleshooting stuff related to compression ratio. So just to see if there's any Smarty Pantes in the room, anybody care to give a quick description of compression ratio? Eli or Matt Was going to talk was H, No, he didn't I I actually called on him No. I I don't Uh. measurement of efficiency of how well the compressor is pumping.

Okay, refrigerant. How well the compressor is pumping Moving refrigerant. That's a good general definition: The ratio of your suction pressure to your head pressure ratio of suction to head pressure. Anyone want to give the specific definition though? No, there's a very specific definition.

Okay, so the specific definition is you take your absolute head pressure and you divide it by by your absolute suction pressure. So how do you take gauge pressure and convert it to absolute pressure? 14 14.7 Okay, so 14.7 What does 14.7 represent right? And so that is the atmospheric pressure. That's the pressure that we see at sea level. So we're sitting at the bottom of an ocean of air, We have an ocean of air stacked on top of us.

It's 14.7 is exerted. So when we're calculating compression ratio, we have to take to account that pressure Because that isn't necessarily always the same. It is here, pretty much always right about 14.7 But if you're in the mountains or in other places, then it isn't necessarily that. So you have to take that into account.

And the reason is is because the fraction that that 14.7 represents as the total amount is significantly greater on the suction side than it is on the head side. And so as we talk about this, suction pressure actually has a greater impact on compression ratio. Small changes in suction pressure than head pressure does just because it's a smaller number. So a smaller change on a smaller number is a higher percentage of the fraction, if that makes sense.

So anyway, when we'll talk about that, So first off, let's talk about uh so I'm I'm going to be throwing up some R410a pressures. Normally, we don't like to talk about pressures. We'd like to talk about saturation temperatures because saturation temperatures matter more as far as when we're troubleshooting and all that. But in the case of compression ratio, we kind of have to talk pressures because you you have to convert to pressure in order to add the uh, the atmospheric pressure to it anyway.

So let's start with static pressure. so you walk up to a system it's not running all right. r410a. A really common pressure would be about 200 PSI and the reason is is because that equates to about 80 degrees.

and by the time you figure inside and outside on a normal day, it's going to be around there. So on a hot summer day, it'll be higher than that. On a cooler day, it'll be lower than that. So you got 200 PSI That's 200 PSI G pounds per square inch gauge.

And that gauge. pressure is zeroed at atmospheric pressure. So in order to convert that to Absolute what do we do? What do we do to convert gauge pressure to absolute pressure? We add 14.7 right? So 14.7 So the total equals 200. And now I'm going to ask some somebody to have a calculator here.

Who wants to? Who wants to be the one with the calculator on their phone? All right, Matt's got the calculator good. So 24.7 So if the system isn't running and our head pressure is this absolute 24.7 What Is our suction pressure going to be 24 24.7 right? So 214 That's going to be our suction. So what is our compression ratio going to be one to one? it's going to be one. Right.

If you divide 214 by 214, what do you get, you get one. So we have a compression ratio of one. Now this is I Like to do this right off the bat because when we talk about compression ratio, and when you think about engineering, people, design these systems, Um, they'll often, uh, say lower compression ratio is better, right? Lower compression ratio equals better efficiency. Well, obviously we have a problem because if the system is not running at all, how efficient is it? Extremely, it's I Mean depends on how you look at it, right? I mean.

In one sense, it's very efficient because it's consuming no power on the other. To the other sense, it's not efficient at all because it's also producing no cooling or heating. so it's neither really right. So it's not really efficient even though it has a low compression ratio.

And actually one Kind of interesting thing is there was actually one fault that you would get and I forget what brand it was. that would basically say low compression ratio when essentially the compressor wasn't pumping at all. And of course, obviously that is the case. It's not running at all.

Um, all right. So when the system comes on, what does it do? well? System comes on. the head pressure goes up from here and the suction pressure goes down from here. That's what the compressor does is it creates a differential head pressure.

Suction pressure. Okay, so what do we expect that compression ratio to be? Well, very rarely are you going to actually calculate compression ratio. You're actually going to look at some other numbers in order to tell you what your head and suction should be. And so what are some common numbers that you would look at to tell you what your head and suction should be? Indoor Driveway You look at the indoor temperature right? You look at your indoor return temperature, and what else would you look at Outdoor? You look at your outdoor ambient temperature.

Those are the two kind of drivers of your head pressure and your suction pressure primarily. And we also know that humidity on the inside does actually have an impact on suction pressure that was Jim Bergman and I's uh, epic battle back in the day. So the one actually won I Don't want to say who won, it was me, but it's fine. Um, all right.

so so let's look at some a typical kind of pressure that you'd see on a R410a system and sort of a normal, you know, mild summer day in Florida So you would see 350. We're just using very round numbers here: PSIG head which is equal to what in Psia 3647, 3647 and then a suction pressure of um, what did I write down here. 118 would be very typical suction, which is equal to what 13 132.0 psia. Okay, so now let's calculate that compression ratio.

so divide 364.5 what is it48 2.74 Eight, Very, very specific compression ratio. and as it turns out, 2.7 2.6 2.8 right in there. That is very, very typical for a modern R410a system. Just a typical system.

Um, that's very. That's very typical. You'll actually see lower than that with higher efficiency systems. The bigger the condenser coil, the bigger the evaporator, the more you're going to see that number drop.

All right, And we're going to talk about that in a second, But that's a pretty normal number that we're looking for. Now let's talk about Refrigeration quickly. Some of you may have had some. You know you've seen some Refrigeration ation systems on refrigeration systems.

You're still tied to the outdoor temperature Cuz where are we rejecting heat to? Generally on big refrigeration systems rejecting it outside Right now? if it's a self-contained we're rejecting it in the store. and so your head pressure is going to be lower because the store is cooler, right? This? Those those are tied together. But if you're ejecting your heat outside, your head pressure as a saturation temperature is going to be about the same that it is for air conditioning. In fact, some cases it's even a little higher.

But in general it's going to be about the same. And the reason is is because you're tied to the outdoor area, you're rejecting heat to the outdoor air. But what is your evaporator temperature going to be on a freezer or a cooler or something like that? It's going to be much lower than it is in an air conditioner. Why? Because the air traveling over that coil is much lower.

Right? If we're trying to get heat out of air, that's 40, you're going to have a much lower suction pressure, right? The reason why we see generally about a 40, you know, 40 Vapor coil. That's kind of our typical. Our typical Vapor coil is because we're about 35 lower than our air traveling over it in order to get heat out of the air traveling over it on the return and get it into that coil and get it rejected out, right? That's that's it's it's. the heat absorber as our evaporator coil.

So on a on a refrigeration system, you're going to see much lower suction pressure. So if you have much lower suction pressure and your head's the pretty much the same in terms of saturation, what's what's that going to do to your compression ratio, it's going to be much higher, right? And so if any of you have ever done something like selecting a compressor for refrigeration or to kind of notice the horsepower, the capacity of a compressor, these are much bigger compressors. Um, for the same overall capacity because the amount of differential the amount of compression ratio that they have to deal with is much higher, right? So it's less efficient per BTU so it takes more watts more energy per BTU when your compression ratio is higher. When that difference is greater, that make sense.

Okay, so let's look at um, uh, let's let's look at older systems. So again, you don't really have that much older R410a systems, but we're still just going to use R410a just so we keep it the same. Uh, in this case, an older system, you would see something like under the same general conditions, you would see about a 400 PSIG which is equal to what Psia 44.7 and you would see uh, something like 107 on the suction. What is that equal to 1217? Math 3.4 That's a very typical compression ratio that you would have seen on older 10 Sear systems 10 12 Sear systems.

That's a big reason why they were 10 SEER systems and not 15, 16, 17 18. What we see today, right is because of the higher compression ratios. What makes up the higher compression ratios? Will you see slightly lower suction, slightly higher head pressure, and it really isn't that much. It's pretty slight, but a slight change makes a big difference, especially on the suction side.

Okay, because in the suction side, the fraction is smaller on the suction side. Any change makes a bigger difference as far as that overall fraction. The smaller number matters more when you're dealing with this sort of equation. So 3.4 When we go to Modern High efficiency systems, let's do another.

Let's do another example. Like really high efficiency systems operating at pretty much the edges of what you can see, that would be 340, which is equal to what 34.7 34.7 And then it would be Uh, 130. And these are these are pressures that you're going to see pretty often on a on a warm summer day, right? These these look pretty familiar to you. It's what we see a lot really commonly.

So what is that? 1447 144.5 2.45 2.45 With 2.3 kind of being the lower limit of what you're generally going to see in terms of compression ratio, you start to get below that. That's actually a sign of a problem, and we're going to talk about that in a second. But what are the consequences of this? Okay, so when we talk about lower head pressure, what is that? What? What do we call that? That's probably a better name than head pressure? What do condensing temperature, right? Okay, we have a lower condensing temperature. How do we achieve a lower condensing temperature? How do you condense the refrigerant at a lower temperature than you did before? What's that cool could could be cooler ambient air, but that's not something we can generally control, right? Our condensers are still sitting in the same Outdoors that they always were air.

Bigger coils could be more air flow Could be bigger coils. Those are your two options, right? And actually more air flow doesn't generally make that much of a difference. It really is. Larger coils is how we get, um, this lower condensing temperature and lower head pressure.

And that's what we see, right? we've seen, and actually it's kind of gotten a little better. There was this period where it got a little ridiculous where they just started like making these gigantic things they realize that doesn't really work for anybody. Nobody wants to carry that around and set that on the outside of their house. But that's the trick.

Make bigger condensor coils. You have more surface area. You have more surface area. You can get closer to that outdoor temperature, but you hit a lower limit, you get to a certain point.

And really, that lower limit is about 12 above outdoor ambient temperature for your condensing temperature. Before you really can't go any lower, you have to have a temperature differential for you to reject heat. I Mean you can, but it gets ridiculous. It gets impractical or you have to go to some other rejection medium like you know, water cooled or something like that.

So it becomes it becomes kind of Impractical on the suction side. What is the consequence of having higher suction pressure? Because we do have higher suction pressure than we used to have most certainly do. What's the consequence of having higher suction pressure? Warmer Coil Warmer Coil Warmer Evaporator Coil What's the consequence of having a warmer evaporator coil can be can be less efficient in some cases. But but if you just take the coil and you make it bigger, you just take the coil and you run more air over it because the same thing on the other side right? So now we're talking about the suction side evapor coil.

You either make the coil bigger, run more air over it. What's the consequence? Colder Coil I mean warmer coil, Warmer coil equals coil higher humidity right? You? You don't remove as much humidity because you're You're now a little bit closer to the D point. The more that you create separation where the evapor coil is a lot colder than the D point of the air moving over it, the more moisture you're going to p out of the air moving over it, So the consequence is is that modern systems that are higher efficient and have warmer evapor coils do not dehumidify as well. Baseline Now they add in this dehumidify mode, it's like hey, well it can go into DEH dehum mode where you drop the blower speed and then it dehumidifies better.

They can do that, but a lot of the time they're operating in not dehumidify mode. which means a lot of the time they are not dehumidifying as well as that old unit that you just pulled out. Okay, so that's important to know, especially when we're selling to clients. These new units dehumidify so well.

Well actually most of the time they don't. Most of the time they dehumidify worse. and when they go into dehum mode, then they dehumidify as well. But that comes at a cost of what.

when you go into dehum mode and that coil gets colder because the air flow drops. What happens to compression ratio: Compression ratio goes up right. Suction pressure goes down. When the when the suction pressure goes down, compression ratio goes up.

There's two things that can affect compression ratio. Outdoor Temperature Outdoor ambient. Anything that drives that condensing temperature up or anything that drives the suction pressure our our suction saturation or evaporator temperature down right? Anything that creates more separation between the head and the suction is an increase in compression ratio. Increasing compression ratio equals less efficient.

Decreasing compression ratio equals more efficient. But when we decrease our compression ratio make it more efficient at the cost of a warmer evaporator coil. Just know it's not dehumidifying as well and that's really important for you guys when you. maybe it isn't because you guys are probably smarter than I was when I first started I didn't have like really great instruction and so I used to go in houses that had air flow problems or Air Balance problems and boy I just love to jack up blower speeds.

That was my secret to everything You know, customer be like it's not blowing any. it's not blowing any cold air in my master bedroom. I' be like hey, I have the solution. Just just take this.

Uh, just take the pin settings on your ECM and just set it up a little bit. Just make that sucker blow air. You know they're solving all the problems and then all of a sudden they start having mold issues in their house. It's like what on Earth I Think we're past statute of limitations where anybody can sue me for that.

So that's why I feel safe to say that you laughed way too hard about that. Elliot's Elliot's a loud laugher. Now we're just going to talk in terms of, uh, kind of more theoretical situations. I Want to just hit on a couple other things.

so Heat pump running in heat mode all right now your evapor coil is outside okay, and your condensor coil is inside. when it's 40. Dees Outside is our suction pressure going to be lower or higher than it was in cool mode? Ler Ler much lower, right? It's going to operate almost more like a freezer or not a freezer, but more like a cooler. Uh, in refrigeration operates, it's going to operate at that sort of suction pressures.

So what's that going to do to compression ratio increase? It's going to increase. That means that it's not going to operate as efficiently. It's also not going to produce as much capacity. The colder it gets outside, the higher the compression ratios go because the lower the suction pressure goes right and again.

Now your condensing temperature is tied to your indoor temperature Because now your condenser is inside in a heat mode. In heat mode on a heat pump, does that make sense? Really big. so it's head and to and to Bird's point when you see when you have air flow problems inside which you know, heaven forbid. we never have airf flow problems on anything we ever installed because we always make sure that the duct works perfect, right? Always.

We always arify that, um, when that thing goes into heat mode now our condenser is inside and so what does that do? And we have an airf flow problem. What does that due to our head pressure in heat mode goes up right? So in a heat pump, especially. A lot. a lot.

of people talk about. um, this kind of ties into the series that we just did about heat pumps a lot of people talk about. You know what's different about heat pumps. Heat pumps are so confusing.

All this stuff. When you're in a furnace market and you have low air flow, it's a problem. But as long as you're within the operational range of the Furnace it's like it's It's just gas on fire and it's not like that big of a deal. But for a heat pump, having low air flow in heat mode is really really bad for efficiency because it drives your head pressure up.

We know head pressure does a lot of bad things. High Head pressure does a lot of bad things to the system. It's more than just efficiency. It's also the compressor runs hot oil breakdown.

Lots of damage can happen, especially to the compressor over time when you have high head pressure operationally. So when we think about the importance of getting air flow right, of making sure that when we're putting systems in, or if we can upgrade systems, or if we can do things that make the indoor air flow better, it's not just because oh, I feel better again I Feel better my master bedroom. It's also that the system is actually operating with lower compression ratio in heat mode. which means that they're getting more BTUs for their Buck Right and the system is going to last longer.

So it's really, really important in heat mode. Make sense. So again, these things all make a difference. What happens in heat mode? If your condenser coil is dirty sorry your outdoor coil, the artist formally known as the condenser coil, your outdoor coil is dirty.

What does that do to your compression ratio? Low suction causes low suction which causes what to your compression ratio. High compression ratio which equals bad efficiency right In Heat mode is cool because we don't have to worry about dehumidification in heat mode, right? We're not trying to dehumidify in heat mode. We can't dehumidify in heat mode, right? The hot coil is inside. We're not dehumidifying so we want to get a lot of air flow inside.

Get as much air flow as you possibly can. Now to back that up a second, you have like on a lot of these heat pumps like the the carriers that we install. They have comfort mode. Okay, have you ever seen that comfort and efficiency mode? All right.

Comfort mode means that they don't run as much air flow on the inside on purpose. And why do they not run as much air flow inside on purpose? In heat mode, Why would you do that to not increase the humidity? When the air hits you, it's more comfortable. It doesn't feel quite as cold. Correct.

So so what is the complaint about heat pumps? Well, the air coming out just doesn't feel like my furnace just isn't as hot, right? Do we want the air coming out of the vents to be hot on a heat pump? No right. In fact, if we're if we're running low air flow in order to get the air hot, what are what are we doing at the expense of head pressure, compression ratio, efficiency, Longevity of the system? A That coil I Mean yeah, you're You're running the coil under higher pressures. There's all sorts of forces that we're doing just because a client doesn't understand how a heat pump should work and a heat pump should not blow air. Now what's the number one rule we're going to back up? This goes back to a this is.

this is sort of a carrot for the for the YouTube AUD podcast audience. The number one rule of Air Flow Design Back to one of my first podcasts I did with Jack Rise. Number one rule of Air Flow Design is you don't blow air on people. You don't blow air on people.

So if people are like I can feel the air blowing on me, that's a problem in the first place. And if you get the client who's like I want to put my hand up there, don't Okay, here's here's what you do. It's like the guy who goes to the doctor and says doctor every time I Do this. My elbow hurts like crazy and the doctor says okay, well stop doing that right.

Same thing with their clients when they put their hand up to the vent I don't I don't feel I don't feel hot air. Okay, well stop doing that. That's not how it works. Leave it set.

Heat pumps do not blow really hot air. They blow warm air and over time it's going to keep your house warm. That's how they work and they're very efficient at it. so it saves you money.

And that's why we like heat pumps. So when we think about compression ratio on the heat pump side, I Wanted to kind of focus here. You want good air flow in heat mode? You want to blow a lot of air over that coil. It doesn't hurt anything.

In heat mode, it hurts nothing other than the possible client complaint because they don't understand how they should work because it's not like it's producing less BTUs Right when you're blowing more air, it's actually producing more. You're actually getting more heat out even though it feels cooler. Does that make sense? And if it's blowing on people, well, then keep it from blowing on people. That's why we don't blow air straight down.

We blow it across the ceiling, right? That's how we're supposed to do it. Another one is inverter system. So when we have a Carrier Infinity uh and it's running in heat mode, a green speed or something like that and it's running in heat mode. Have you ever been on a really cold day when when you set the temperature your way up on one of these heat pumps and listen to how that outdoor unit sounds? What does it sound like sounds absolutely upset.

It sounds upset. It sounds cranky. Same thing is true with the ductless system. Anything that is an inverter heat pump that's designed to produce a lot of heat at low temperatures, How do you think it does that? How does it magically? you'll see some.

will'll be call them hyper heat. They'll call them high heat. They're just designed to produce a lot of heat, even at low temperatures. That's good.

I'm glad they do. but how do they do it? l Condenser fan and the compressor higher. Uh, they don't usually lower the condenser fan. that's usually not.

I Mean that actually? No. I Actually have seen some do that and that does make sense. Yeah, it drives the compressor higher though. So to your point, yes, it drives the compressor higher.

It spins the compressor faster. That's what it does on these inverter driven compressors. so you're basically overclocking the compressor. Those of you who are in the computer World never do that right.

It's it's you're spinning that compressor faster than it would normally be designed for. In the past, we couldn't do that. Now nowadays we can do it because we have better compressor technology with Interstage Cooling and other things that we can do to keep it cool, right? So in the past we couldn't do that because the compressor would overheat. But what are we doing to compression ratio? When we spin the compressor faster, we're increasing it.

We're doing it on purpose because our other option our only other option to heat the house is to turn on heat strips. So it's better to overclock the compressor than it is to run heat strips in terms of efficiency. But is it efficient? Well, the answer is no. Not compared to these systems running in cool mode, right? So once again again, this is the reason why we don't want in heat mode to have a lot of this catchup where we let it get cold in a house and then we catch up.

That kind of thing because you do it at the expense of something. It's always better in our Market Especially where we don't have these extreme temperatures. just set it and forget it. you know, set it to a temperature and just let it operate at that temperature.

Something reasonable. You don't want to have all this because those BTUs when that compressor spinning like crazy trying to catch up are much more costly than they are when it's just cruising. Make sense. Higher ression ratio.

All right. Final thing is what we see when you actually have a fault: an actual problem. When we have a situation where the uh, the refrigerant going into the compressor is not being elevated at an appropriate amount. So let's say 310 PSI we won't even bother converting it to Psia because we're not actually trying again.

This is where, like, if you're using something like measurequick, compression ratios are readily accessible. Very rarely in the field are you going to be like. All right, got. take my pressure, add 14.7 14.7 Do the math.

That's not really what you're going to be doing in most cases. Um, but if you see something like this where it's 310 PSI head 310 that way, and uh, we'll say 150 suction. Okay, that indicates a problem, right? because now your suction saturation pressure is up above like 50. That's not great.

It would have to be really hot in the house for that to make sense and especially doesn't make sense with head pressure that low. Do the math real quick on what this is. compression ratio. What's that? 2.

So and again, we didn't add the 14. did you add the 14.7 to both sides? so we would have to add that? And that's so that was stupid. I said we weren going to do it and then I said to do it. Um, but regardless, it's a low compression ratio.

It's a compression ratio that's down below 2.3 Whenever you see a compression ratio, an operating compression ratio that's down below 2.3 it's an indication that something's going wrong. There's a compression problem. So remember when I said low compression ratio is good for efficiency. There's a caveat if everything's working the way it's supposed to.

and the problem is, how do you know if a compressor is working the way it's supposed to by the compression ratio? So it's like this circular logic problem, right? So there are ways you can go to. For example, you can use the Copeland mobile app and there's actually a place that you can put in what all your pressures are and what your amperages are and it will tell you whether or not that compressor is operating the way that it's it's supposed to. whe It's operating as expected. it's really handy, and in commercial world we should be absolutely using that all the time because it's really a great tool.

But out in the field for us, the really the only way in residential that you're going to have this readily available for all compressors is just good old common sense. right? when you start to see everything else is operating as it should. everything's clean, There's nothing surprising. air flows.

There's nothing crazy. The pins aren't set wrong in the blower where it's you know, blowing way more air over it than it's supposed to. There's these sorts of things you have to look at, but once you've established that and your compression ratio is too low, there's really two primary reasons that that happens on a heat pump. What are the two primary reasons that you get a compression ratio that's well, lower than it should be? Inverter system is one.

St It's actually like a Min split right as it's satisfying. All right birds being cute so that's not one of the two, but that's fine. Go ahead. Go ahead say say it a little louder.

Inver Compressor system Like a mini split when they are just maintaining temperature, the compressor will R down. Or if you're in, well, you're probably going to do two stage. So if you're low, if you're staged down right, that is true. If you're staged down, you will get lower compression ratios, it'll be on the edge still of that sort of 2.3 2.2 Like, you're not going to get that much lower than that because eventually you just stop moving heat.

but you are going to get a little bit lower. So if inverter where it's spinning the compressor not as fast uh, multistage equipment where it's in low stage, you're going to see those lower compression ratios. That that is true. But let's say there's a problem.

There's actually you're actually troubleshooting it. You you know you're on high stage, so that's something you want to make sure when you're troubleshooting, are you on high stage? Um, what do you? What do you look at next? The metering device metering device is actually the third and I would say probably the least common cause of truly low compression ratio air flow and charge. Air flow and charge is something that you should look at. But again, this is low compression ratio.

Low compression compression ratio is normally not going to show up with air flow and charge it's usually going to you. do. You would absolutely check Amperage that. So to your point, you do check those things.

and I probably didn't ask the question right? I Get ahead of myself. Sometimes you those are things that you check in troubleshooting air flow. Charge Amperage. Those are things you check.

But what are the actual underlying causes at this point that we're kind of looking at? there's two primary underlying causes for really low compression ratio: Compressor Compressor that is not pumping appropriately. Okay, we we like to use so so we use terms like a slipping compressor or bad valves or whatever. But again, there's a lot of different types of compressors: a rotary compressor, a scroll compressor, Reip compressor. They have different types of faults that can cause them to not pump properly and we are not going to know what that is unless we take that compressor and cut its head off and take a look inside later.

Do a little autopsy on it, right? And by by the way we are getting, we're making a compressor cutting machine that Roman is very excited about And I'm excited too. So whenever we get weird problems with compressors, we're going to cut them open and look at the inside of them. So that is a fun thing, just you just take one with you in the feel it you just like see what we've done to your brothers. Do you? Are you sure? Are you sure you want to act up? It's it's it's avoidance, it's dark, It's really dark.

Uh, anyway, so we don't really know usually why it's not pumping. We don't know why it's doesn't have full compression. Um, but often that's the cause. now you have to be really careful because in a lot of compressors there are safeties that produce poor compression on purpose, right? A lot of scroll compressors have this some sort of internal Bypass or you know, uh, Copeland calls it radial and axial compliance.

Which means that the Scrolls have Springs in them and they can actually move this way and this way a little bit in order to allow, uh, bypass intentionally so they don't damage themselves. You have things like digital Scrolls Have you ever anybody ever heard of digital scroll before? You have J So you're like you're like, really in the refrigeration world. Now you know this stuff. Digital.

Scrolls They sound like absolute death and murder. I Mean they just they sound like something is definitely wrong. But what they're doing is they are actually engaging and disengaging. Engaging and disengaging.

So they do this like this. Really? That was a terrible, terrible example, but they make it sounds like they're going on and off and like something really bad is happening inside of them. But that's actually a design. It's it's their.

they're engaging and disengaging as a way of unloading. so a way of producing uh, less than full capacity. Um, it's and and they're designed for it. It doesn't sound like they should be, but they are designed for that and so you do have to be careful a lot of times.

The reason why a compressor is not pumping is because of something else. Caused that to happen temporarily and if you let it, if you shut it off and let it reset, then it will often run properly. One really common thing we see in residential and every time I Say this. we get some guy on YouTube who tells me that this doesn't happen and then we turn around and see it happen all the time is that compressors will run backwards.

Okay, there's a particular brand that will be unnamed, but it's where the compressors will sometimes run backwards if the system is short cycled. Okay, so if the system goes on and off real quick, what? H what's happening is and this is I mean I'm iing this, but it's pretty obvious. What happens is is that the compressor starts moving backwards slightly as it's equalizing pressure and then the power comes back on and it and it starts running the wrong direction. It sounds really bad and it doesn't pump at all.

Or almost none. A scroll running backwards doesn't pump very well. It's not designed to, you know, not designed to. run backwards.

So what do you do in that case? You shut the power off, let the pressure equalize, and then you turn it back on and it works fine, right? So best thing to do is make sure you have time delay in it. so that way it doesn't do that so it doesn't short cycle. Okay, so you have to be careful about this. but once you've eliminated all of that, it's not supposed to be doing this.

There's not some other Factor that's causing it. You've shut it down, you've let it cool down, you've let it reset, turned it back on. Still doing the same thing. Your compressor is your number one culprit.

It's generally the most common cause the next is your reversing valve. Reversing valves can get stuck halfway U that actual little. There's a little we call it a canoe that kind of slides back and forth in there and if that canoe gets stuck halfway. Now the trick there is is that sometimes the canoe gets stuck halfway because the compressor not pumping because what is required for that slide to work in a reversing valve pressure difference, right? So if you don't have pressure difference, then sometimes that canoe will get stuck because of that.

and then you blame the poor reversing valve. And trust me, if you want to blame one of the two, the compressor is much nicer to blame because he's much easier to change than the reversing valve. Who here has brazed in a reversing valve before. It is no bueno.

It is not fun. It is. it is not good, right? So, and statistic Bally It's the compressor more so. Now can it be the TXV or the metering device Burt that causes low compression ratio? It can.

And in that situation, the big difference is going to be that you're going to have zero super heat because your TXV is going to be wide open. So you're going to. uh. Typically, when you have a slipping compressor, you're still going to have a decent super heat.

You have a high suction, but you're also going to have a warm line. but with the metering device wide open, you can't escape the zero super heat. Change your air, you, whatever. but you're still stuck with zero superheat.

I'm going to add a caveat: What is your superheat When the system is not running at all Zero. Go up to do it sometime. Go up to a system, hook up your your your field piece you know, fancy probes, or your digital manifold and set it up for superheat with it off and then look and see what it says. What's your subcooling Zero Zero right? So here's the problem with what Bur just said.

This is great. Not not criticizing because it's true, but you will also run zero superheat if the compressor is not pumping at all. So as that compressor gets closer to not pumping at all, you can also see Zero superheat. The way you troubleshoot a reversing valve is you look for temperature differential across the valve right.

especially on the suction side because that's where you're going to see it more. The two pipes that are both suction you shouldn't see in I Generally say an 8 degree. That's a little bit liberal. Um, you shouldn't see more than an 8 degree difference across those two.

And then if we have a heat pump and so we before I troubleshoot the reversing valve I'll switch it into he and see the compression ratio across my heat pump metering device. Correct. Very good. Very good.

Yeah. so and and and even if it's warm outside, you can do that for a short period of time you can see. Is it pumping right? Um You can. Also, back in the day, we used to do pump down tests.

What's the problem of doing a pump down test? Nowadays that's how we used to test compressors. See: Could they pump down? What's the problem nowadays with pumping down? What's that? Yeah. So the compressors. A lot of scroll compressors don't let you pump them down.

You get down to a certain level and then they go into bypass, right? And that bypass is exactly what I'm talking about. It's a designed compression com ratio safety. Basically, it prevents it from going into too high of a compression ratio. CU That's what's happening as the suction drops again, back to compression ratio.

as the suction drops on that compressor. What's happening to the compression ratio? Higher and higher And higher and higher. So when you're pumping down a compressor, that compression ratio is really high. which is actually why pump down is not something you want to do all the time.

Now for those of you who know anything about Refrigeration, you're going to say hold on a second. What about Automatic Pump Down Refrigeration systems. Because there are systems that pump themselves down every time they shut off. In fact, that's how they cycle is.

They cycle by pumping themselves down. It's a nice strategy because you don't have uh, refrigerant migration and therefore you don't have oil issues as often. Um, so that's a nice strategy, but but what do you have to do then? that sounds like a real problem. Well, the trick is when you do a pump down system.

you don't pump it down to a really low suction pressure. You just pump it down. You just pump it down till all the liquid is pumped into the condenser and then you shut it off. It doesn't.

You don't have to get it down to a really low suction pressure when we're pumping it down and trying to open it to Atmosphere To do service. of course, we have to pump it down to zero and that's where it becomes a challenge. That's Where It's Tricky And so Old-Timers Used to pump down compressors on purpose to see if the compressor was pumping properly. That was a test they used to use and nowadays that's become more difficult.

Like everything else, you know, you know, the good old days we had R22 We could vent it to the atmosphere whenever we wanted. Kidding I'm kidding EPA That never happened. Identifying a compressor, Um, that it's going into bypass for some other reason. Like it's operating properly.

The most common is that you're over Char You have high head for some reason or another and so if you turn it off and you let the compressor completely stabilize and then you turn it back on, watching your head pressure, it may go into bypass again within 5 seconds if the issue is Extreme enough. If you're that much overcharged within 5, Seconds it could go into to bypass again. But if you've equalized and you turn it on, you sit there and you watch your gauges, you're going to see that high. Spike You're going to go up above 500.

PSI All of a sudden boom, that compressor is going to shift in the bypass. You'll hear it. You'll see, see it happen. Yeah, whereas a compressor that's not pumping isn't going to be capable of doing that right.

Cuz what are we saying When it's not pumping, that means it can't do this. It can't bring the head pressure up and the suction pressure down. So it's kind of a complicated topic. It's one of the most difficult troubleshooting tasks.

Just know that when you run into this first thing I want you to do is be able to identify it. Hey, this is a compression problem. My compression ratio is, you know, I'm in high stage and my compression ratio is below that 2.3 number. There's an indication of something going wrong.

Now again, if you're working on a refrigeration system where you're running in heat mode, 2.3 would be way too low, right? So I'm talking about cooling under normal conditions, go ahead. B Sure, um, or than ever before in my Uh 10 year historic career. Uh, we are running into compression ratios that are lower than we've ever seen before on systems that are working the way they were designed. Because a lot of systems are doing the high efficiency coils inside and outside, they're just making them a little bit bit bigger for a little bit better number.

Uh, recently we're just working on a two-stage and the compression ratio was 2.1 and we had humidity issues in the house and um I I Called Roman with all my numbers and he was like actually this is right on target with design because they're trying to hit a little bit better efficiency number with the design of this equipment. they have a really large coil they have. They actually increase their outdoor fan speed a little bit more even to bring the head down a little bit more than we were used to. And uh, so yeah, you are you are going to see on that low.

Edge Even if it's not fully variable, it could be just a two stage. It could be running in full stage, but more than ever. I'm getting calls from people where everything is as it's supposed to be. My amps aren't crazy.

Uh, on the compressor than not low like a slipping system, maybe slightly lower because it's running more efficient, but not like lower than 50% of what they the uh Rla is. And then here we are. Um, still not exactly comfortable. hardly getting better than a 17 18 degree split at 400 CFM per ton that sort of thing.

So just putting that on the radar that that I'm a disconnected Oldtimer and I don't know what it's like out there these days. I Didn't want to say it like that. However, there are manur, hey hey hey hey easy manufacturers are cheating a bit with this and so you're not seeing the numbers that you want to on compression ratio and on the head pressure side, that's fine. The head pressure side.

There's no other than just having to deal with a gigantic unit. Um, no big deal, but on the on the suction side, on the evaporator side when you're in a high latent Market which we are. there's very few markets that are worse than us in terms of do points. Um, you you want to try to then drop down your F your your your fan speed in order to get a little bit better dehumidification so it's just something to watch for.

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