Frozen Evap Coil Troubleshooting: Liquid Line Restriction, Low Airflow, Low Charge!

hey guys this is crema clay uh trio from AC service tech and today what we're going over is how to tell what the problem is when you have a frozen evaporator quill so I'm gonna be going over some of the indicators to tell which of the three problems it could be and these three problems are low refrigerant charge low indoor air flow or liquid line restriction when you arrive at the site and if the evaporator coil is still frozen at the indoor unit you can hook up your gauges and continue to let that run and check your sub cooling you're also gonna need to know what refrigerants in the unit but in this instance is are for tonight and on our red gauge we read two hundred and thirty-five PSIG if we bring that into the saturated temperature on the inner ring for our for tonight we read eighty degrees on our temp meter on the liquid line if we only read 78 degrees then we know that the sub poins only two degrees so it's sub cooling as the saturated temperature of eighty degrees minus 78 degrees and that equals two degrees of subcode when you have a sub coin that's that low you know that you are low on refrigerant even before you defrost out of a protocol so if it's only one to three degrees of sub cooling then you can determine that the problem is not a low airflow problem and that's not a liquid line restriction problem so we normally check the refrigerant charge of a TX v with sub cooling and we check the refrigerant charge of a fixed orifice system that has say a piston or a capillary tube we check the total superheat with the blue gauge and the vapor line however you're going to be able to tell that the system is low and refrigerant just based on that very very low sub coin now say instead we had a pressure of 297 psi G and we bring that into the inner ring for our for tonight and we find the saturated temperature of 95 degrees and on our temp meter on the liquid lines say we read 85 degrees that means that we have 10 degrees of sub going so if you read that then you know that you're not low on refrigerant so you know that that's not the problem the next thing that you need to do is to defrost that that evaporator coil so you need to make sure that you turn that compressor off and either a wait or try to defrost that coil somehow after that's completely defrosted the first thing that you want to do is to check for air flow we have some videos for checking air flow such as a temp rise formula if you have a air handler with electric resistance in it and we have videos on checking the static pressure for the tes P which is a total external static pressure and comparing that to the manufacturers data we have another video on checking the air flow with the hot wire anemometer you can also check it with a rotating bean anemometer or with a flow capture hood so right there you should be able to determine if you have a low air flow problem right there but anyway if we were to go ahead and turn the system on when you have a defrost at evaporator coil we're gonna also need to know if we have a TXV metering device or a fixed orphis metering device such as a piston or capillary tube so you're gonna be able to see that at the indoor evaporator coil now if the system had a liquid line restriction problem it's not gonna matter really what type of metering device you have a liquid line restriction problem could be that you have a a clogged strainer by the metering device or maybe a clogged filter dryer or maybe a clogged metering device such as a DX v that's lost its bulb pressure and is no longer opening properly but the indicators for liquid I restriction problem are going to be the same regardless of whether you have a fixed office or a TX V however the indicators are different for a low airflow problem so the first thing that you're gonna monitor within the first few minutes of runtime once you get that system up and running is the vapor pressure so you're gonna look at the vapor pressure and in this instance we have a vapor pressure on the blue gauge of 97 psig we bring that into the inner ring for R for tonight because the system has r410a refrigerant inside and we read 30 degrees as a saturated temperature if we had a temperature on the vapor line of say 65 degrees then we know that we have 35 degrees of superheat and that's a high superheat so if we had a high superheat that's an indicator of a liquid line restriction problem and not low indoor air flow if we have a t --xv as the metering device and we have a saturated temperature of 30 degrees and on the vapor line we read a temperature of say 44 degrees and that's only 14 degrees of superheat and that's a kind of a normal super heat and the t --xv is gonna be able to hold that superheat fairly steady even if you have a low indoor air flow problem it's not going to be able to hold it if there's no air flow whatsoever but in a slightly low air flow situation that t --xv is going to be able to hold that super heat correctly somewheres between say 1014 degrees or maybe e to 17 degrees it's gonna be somewheres probably in that range there remember at the outdoor unit we are checking total superheat because we're not able to check a pressure and convert it to saturated temperature right by the evaporator coil we have to check our refrigerant charge with the available pressure port at the outdoor unit so that's referred to as total superheat so we already have an idea of where we're heading with this just by the superheat reading for a low airflow problem your sub going measured on your red gage and with on your liquid line is gonna be probably normal to high and for a liquid line restriction is going to be high if you look at the red liquid gage and you read a pressure of 297 PSIG you can bring that into the inner ring for r410a and you see 95 degrees saturated temperature then you read the line temperature on the liquid line and you read eighty degrees that would be 95 degrees saturated temperature minus 80 degrees line temperature and that leaves you with 15 degrees of sub corn and that's a little high it's not it's not astronomically high but that can kind of lean towards a liquid line restriction problem but once again the sub point is not gonna give you too too much information you know you might read say a saturated temperature of 95 degrees and an actual line temperature of 85 degrees then that leaves you with 10 degrees a sub cool and that would be kind of a normal sub 4 so once again you really want to rely on your own your total superheat on this you can also go inside and check your delta T when you have a liquid line restriction problem you're gonna have a low delta T so in the return we have a temperature of 72 degrees and in the supply we have a temperature of 60 degrees so that leaves us with a delta T of only 12 degrees so that would be an indicator of a liquid line restriction problem we're not able to get enough refrigerant to the evaporator coil to absorb the heat in the house therefore we have a very low delta T for a low airflow problem the TX V is able to monitor and hold the superheat and so if we read say 72 degrees on the return then we might get a measurement on the supply in this case of 54 degrees so that means that we have a delta T of 18 degrees so if you have a normal or maybe high delta T that would be a low indoor air flow problem both the vapor sat temp and the liquid sat temp on the gauges are going to be low regardless of whether you have a low indoor air flow problem or liquid line restriction problem and that's because you're really just you're not absorbing much of the heat from the the inside of the building so now let's move on to a fixed orphis so if you have a fixed orifice metering device you're gonna have the same thing your your liquid line restriction problems gonna have a high superheat a high sub cooling a low delta T and low vapor set temp and a low liquid set tub but if you have a low indoor air flow problem the superheat is going to be low so let's look at the blue vapor gage and if we read a pressure there of 97 PSIG and we convert that to 30 degrees and on the vapor line we read a temperature of 33 degrees then that means that we have 33 degrees is our line temp minus or 30 degrees as our saturated templum we're left with three degrees of total superheat so that's very very low if on our temp meter we read a temperature of say 65 or say even 70 degrees say we read 70 degrees as our line temp 70 degrees minus 30 and we're left with 40 degrees of total superheat so if you have a high total superheat you know you have a liquid line restriction problem if you have a low total superheat then you know you have a low indoor air flow problem so you got to remember that the fixed orifice is not going to be able to slow down the amount of refrigerant that's heading into that evaporator coil so you're still gonna be flooding that evaporator coil with low pressure low temperature liquid refrigerant and it's absorbing the heat from the air and you're just not left with that with a lot of superheat it's very low whereas a liquid line restriction would mean that it's it's slowing down the flow of the liquid refrigerant into the evaporator quill and when you don't have much refrigerant in the evaporator cool to absorb the heat load in the house the superheat is going to be very high if we go into the house and we read a returned temperature of say 74 degrees and we read a temperature on the supply of 50 degrees then that's 24 degrees as a delta T and that's high that's a telltale indicator that we have low indoor air flow problem if it's a fixed orphis system if our delta T is low and we have a return temperature of 74 degrees but we only have a supply temperature of say 61 degrees then that means that we have 13 degrees as our delta T and that's low in a liquid liner restriction problem you may even have say 8 degrees or 9 degrees as a delta T it's going to be real low if you want to learn more about troubleshooting air conditioning systems check out our book and the book is written in layman's terms so it's it's easy to understand even if you're just coming into the trade and you're new we take you through from the the beginning like how the system works with a refrigeration cycle how to check the refrigerant charge and then we move into the troubleshooting aspect so there's some in there for just about everybody you can check out our book and the quick reference cards move our website at easy service stay calm and we also have these products available over at amazon.com you can also check out our workbook which is a thousand questions that'll help you understand and apply what we're teaching in the book and that workbook comes with an answer key so it's a self-study edition you can also get our book as an e-book and that's available over at Google Play and also at our website AC service tech comm if you want to learn more about what we do check out AC service stay calm and also facebook.com slash AC service tech hope you enjoyed yourself and we'll see you next time EC service tech channel

Channel: AC Service Tech LLC

Views: 125,569

Keywords: acservicetech, repair, maintenance, how to, fix, hvac, hvacr, how do you, test, ac, service, tech, check, measure, read, superheat, subcooling, refrigerant, procedure, voltage, charging, temp, multimeter, freon, troubleshooting, frozen, freeze, evaporator, evap, coil, ice, iced up, liquid line restriction, low indoor airflow, low refrigerant charge, amount, low, pressure, temperature, saturated, line, diagnose, diagnosing, airflow

Id: wZctpvMtXMM

Length: 10min 13sec (613 seconds)

Published: Sat May 09 2020