Hey thanks for watching this video. This is a next in the series of our HVAC refrigerant diagnostic, quick sheet kind of talking through some of the symptoms of common system failures, and so today we're gon na talk about low evaporator air flow, most common cause of low evaporator air flow, probably being a Dirty air filter, everybody knows the old dirty air filter situation, but if you want to get this quick sheet that we're going over today for yourself then go to HVAC our school comm forward. Slash quick dash sheet also watch the other videos in this series. They all have similar artwork they're easy to find the one on overcharge under charge are also gon na.

Do them on liquid line restrictions, dirty condensers, other topics, but there's a lot of consistent themes within this series. One of the first things that you have to know really well in order to find these problems is what your acceptable ranges are. What your target ranges are you can find out more by going to the article that's shown on screen, that's also down in the description which is about my five pillars: the five common things that you need to be checking when you are doing an in-depth diagnosis of A refrigerant circuit there's a lot more than that, but this is sort of the five to start with and you sort of use these as building blocks in order to figure out what's going on with the system. So if you take a look at this chart, up top, we've got a fixed metering device type of system, and then we have a TXV system below we're, focusing on the low indoor air flow, low return, air temperature and if you go down below the same thing, Low indoor air flow, low return, air temperature, but the chart up top is for fixed metering device, which would be a piston or a capillary tube.

Something like that and then down below are the symptoms that you see for a TXV system like I've mentioned before. We've got little white stars as sort of your key diagnostic indicators. It's not that the other ones don't matter, but they're gon na be a little tougher to follow for this problem. But when you're looking for a particularly a low indoor air flow low return air temperature, you really want to look at suction pressure and superheat.

Let's even make it more simple than this. Okay. In order to find your most common air flow problems, you really need to be inspecting visually. So look at your air filter.

Look at your evaporator coil. Take a look at your ductwork. Take a look at your return. Air grills make sure that they're not impeded.

You know somebody doesn't stick a couch up in front of your return: air grill if it's a wall grill make sure to visually inspect what you, those are all really good practices that will eliminate a lot of the need for this in-depth diagnosis. Many times you find the dirty filter, you don't have to have checked. You know hooked up gauges to ensure that you have a dirty filter, so always use your visual inspections, I'm a really big fan of using visual inspection. But let's make this simple: you walk up to a system.

First thing you may notice on a system that is low, airflow is icing if you walk up and you see ice coming out on the suction line on that coil or on that air handler or if you go outside, and you see an iced up suction line. Going to the compressor, the reason that that happens is because your evaporator temperature has dropped to low when your evaporator temperature drops too low and it drops below 32 degrees Fahrenheit for a long enough run time that water, that's condensing on that evaporator coil is going to Freeze causing ice and that ice is going to creep its way down the suction line. When you see an iced up, compressor or ice leading up to the compressor, it didn't start there. It started in the evaporator coil because that evaporator coil was below 32 degrees and then it eventually crept its way back and when we think about that 32 degrees.

We already talked about this - that is a 32 degree, saturation temperature. So if you go to the refrigerants slider app that I always use the Danfoss app, that makes it really easy. We're gon na put it on make sure that it son gay juh, the toggle, is on gauge pressure and then we're going to set that to 32 degrees, and you can see that's a hundred and one PSI. So if you have a system that runs below 101 psi suction pressure, which equates to a 32 degree, evaporator temperature or 32 degree suction saturation for long enough, that's going to result in a freezing of a protocol.

But in many cases either hasn't run long enough or it isn't quite to that freezing level, and you still have an airflow problem and in those cases one of the primary indicators. When you walk up to that system, you can touch that suction line, and I suggest that you do you don't use grabbing the suction line and grabbing the liquid line as a measurement. But you can use it to help, get you moving in the right direction and when you grab a suction line and it is very cold - that's either an indication that the system is working properly and you may just have low evaporator load like maybe it's really cold. Inside something like that, or maybe it's in dehumidification mode, what the system is trying to run low evaporator airflow on purpose.

But you know that when you have a really cold suction line, coming back to that compressor colder than what you're used to feeling that generally you're gon na have a low indoor airflow, because there's very few other things that can cause that in a fixed metering devices To you can maybe run a lower into the normal suction temperature. If you have an overcharge slightly something like that, but in general, if you do the math pretty simply if it's a 75 degree indoor temperature, our rule of thumb, is a 35 degree design temperature difference between indoor and evaporator. That would be a 40 degree of a protocol, then add 10 to 20 degrees for superheat 10 degrees inside 20 degrees being typical for your outside superheat, meaning at the compressor. So that means that you're going to have a range between 50 and 60 degrees suction line.

If you grab that - and you can tell it's in that range or colder, then that's generally gon na be an indication that you want to start looking on the airflow side, if you're having a system problem where it's not keeping up or it's not cooling well or Whatever the case may be, when you actually connect to the system, what that's going to show on this chart here is you're going to see low suction pressure and you're gon na see low superheat, which means low suction pressure and low suction temperature, because again superheat just To cover it one more time, you take your actual suction line temperature and you subtract your suction saturation or your evaporator temperature, which again is that temperature that you use a PT chart or a nap or measure quick or whatever in order to get that correlation between Your pressure and temperature that differential superheat, which means that again, when you have low air flow, you're gon na, have a low suction temperature and you're gon na have low pressure, which is what differentiates it from other things that can cause low suction pressure like under charge Or a restriction so back up, let's make this really simple: if you have low suction pressure and low suction temperature ie low superheat, that means you need to be looking at air flow. It's just that simple. I mean our there's some really exotic combo problems that could be going on it's yeah sure, maybe possibly I mean somebody could have put the wrong refrigerant in it. For that matter, there's always some weird edge cases, but let's focus on the basics.

When you walk up to a system and it's got low suction pressure and below suction temperature, ie low or good superheat, so either correct superheat in range or low, that's an indication that you have low airflow full stop now, there's some other things here. So, let's look at fixed metering device. What you'll notice is on a fixed metering device. Your superheat will be low when you have a low airflow on a fix mating device.

If you have low airflow you're gon na have low superheat and low suction pressure. When you have a TXV system, you are not necessarily going to have low superheat now I show it here on this chart because it does tend to creep down a little bit and I didn't want to try to explain this a whole lot, but it's really gon Na be normal to low, so if you're used to seeing a 10 degree superheat on this system, when you have low airflow, it may be down to 8. Something like that. So it's not gon na go to 0, because the TX fees job is to maintain superheat.

Now we know that the TX fee doesn't maintain a single number. It maintains it within a range, but regardless, when we have low airflow you're, going to notice that you still have a cold suction line with low suction pressure, what I see Tech's do all the time with the TX fee system. Is they see that low suction pressure and they start adding refrigerant, you don't add refrigerant, just based on low suction pressure. You have to also look at that suction temperature and measure superheat.

If you measure low suction pressure and you measure normal to low superheat, normal Tolosa breathing, and that varies depending on where you're measuring it length the line set a few other things there. But if it's normal to low and low suction pressure, you need to be looking at indoor air flow or indoor load. So when I say indoor load, that would simply mean in most the most of what we deal with. You could have a really cold inside temperature.

Somebody could have tried to set their air conditioner 65 degrees that would be low load and it's going to look essentially the same as low airflow. You're gon na see low suction you're gon na see normal to low superheat and you're gon na see a high delta T. That's another indication now the only reason that I don't call high delta T a primary indicator is because delta T is a pretty big range, depending on your indoor, humidity conditions and your system capacity, you could have a delta T anywhere from 16 to 22. You know, depending as your target and so just because you see a 22 degree delta T that doesn't necessarily mean you have a low airflow right now, if you see 24 25 pretty good indication, you've got low air flow, but also there's a lot of factors that Impact how accurate a delta T is taken again we take in the return we take in the supply when that split is bigger.

That difference is bigger. That's an indication, one of the indications of low air flow, but again because the range is so big. I don't make that the primary indicator, so let's go through them all very quickly. What are you gon na see when you have low load, you're gon na have low suction pressure.

You're gon na have low head pressure. I say normal to low when you have low. It's gon na be low head pressure as well. The reason why it's not necessarily a primary indicator is because it really does depend on what that outdoor temperature is, and so you make you're gon na see kind of normal below super heats gon na be low.

Your sub cool is going to be normal to low, and your compressor amps are gon na, be normal, too low. Again compressor. Amps are always kind of trick, they're hard to see as a primary indicator of anything, because we don't really know what too high and too low is we know what way too high is, if that's, if you're, actually over the run load. Amps that's listed on the data plate, but that's gon na be very rare, but your delta T is going to be high again.

If you use the measure quick app. The measure quick app is going to adjust those targets for you, along with your indoor and outdoor load conditions, and so those targets will be much more accurate. One of the big things that we face in the industry is that people try to use fixed targets to say all right. Well, my suction pressure should be this well.

Your suction pressure is only going to be that at a given set of conditions and your targets have to adjust for those conditions, which is why you need to know. What's in the five pillars, article you need to know the basic terms like CTO, a and DT D and delta T and superheating sub cool and all those things, and if you don't know those things yet no big deal. This isn't a waste because you still learned that when you have a low suction pressure and low suction line temperature, that's an indication of low air flow you're having a hard time finding where the air flow problem is. This would be a really good time to look into the manual of the piece of equipment.

You're working on make sure that all the settings are right make sure that the ywír is put on the right terminal. Make sure you have a G call in cooling. A lot of variable speed equipment, if you don't have 24 volts on the g terminal at the fan, coil or furnace, or if you don't have that yellow wire landed on the right terminal that can cause low airflow. You have a dehumidification terminal, that's not being energized.

The way it's supposed to vacuum cause low airflow, and then you can also check your static pressure, put a probe in the return put a probe in the supply. The new fill piece. Joblink probes are great for this because you can monitor separately and see which one has that higher static reading, which is going to be an indication of something to look for. If maybe you have a locked return or a dirty filter, or maybe a filter that got jammed up into the return and got lost in there somewhere, kinked duct there's a lot of things that can cause airflow issues on a piece of equipment.

In addition to the obvious ones, but a really big thing and modern equipment is the settings make a big difference. If you have the settings wrong, then that's going to impact everything and you're gon na have a really hard time finding it. A lot of people will say: well, the airflow is good. What do you mean by the airflow is good? You mean you visually inspected, it that's step one but step two is you need to make sure everything's set up properly and then step three would be using your static pressure, probes and then actually measuring your static pressure step, four, which I would love more people to Do is actually measure the airflow with a hot wire, anemometer, airflow hood or even better, yet the true flow grid from the energy conservatory, which is probably the best way of measuring total system airflow.

Those are all kind of next-level things. If you don't know what the heck, I'm talking about check out bills, phones, video on the true tech tools, channel about air flow, there's a whole series of air flow videos on that channel that you can learn more about how to measure air flow. But again when people say the air flow is good, there's no such thing as good air flow. There is a particular measurement, and until you get to the point that you're really measuring air flow with something like the true flow grid, you don't know that the air flow is good.

A lot of what we're doing is process of elimination, we're checking what we can check and again, at the end of the day, we're wanting to get our suction pressure near the target or in again our superheat near the target. We're gon na get our delta T near the target and once all those are in line now, we have a pretty good indication that our air flows, where it's supposed to be now again that doesn't deal with compound problems. We have more than one thing you know. Maybe the system is overcharged and has low air flow and has a expansion valve that's not responding properly or a compressor, not pumping, that's where it gets really complicated, but as technicians we eliminate one variable at a time.

It's the scientific method. We eliminate one variable at a time we isolate, we figure out what's wrong here we deal with that and then we move on to the next and that's again where the measure quick app is really helpful, because it's not only gon na give you the primary suggestions. It's also gon na give you some other things to check which will help you quite a bit. Low evaporator load means that you're not exposing that I've Aperta quote to as much heat, which is generally due to low airflow moving over that of a per two coil.

That indoor coil you're gon na see low suction pressure load, a normal head pressure, low superheat load, a normal sub cool, low compressor, amps and high delta T. Those are your primary indications of low indoor air flow. Alright, those are some things to watch for, hopefully you found this helpful you're gon na be more coming in this series. So stay tuned talk to you soon.