Charging an R-410A AC Unit that is Very Low on Refrigerant with the Subcooling Method!

this is chris migliaccio from aec service tech and today what we're going over is we're adding r410a refrigerant into this running air conditioning system because it's very low on refrigerant we're going to be moving the cameras up close so that you can monitor the pressures and the temperatures as we add the refrigerant coming up [Music] before we get started make sure to check out our refrigerant charging and service procedures for air conditioning book our thousand question workbook and our quick reference cards all available over at ac servicestick.com now we're going to get into it before we connect our hoses and add our for tonight into this air conditioning system i want to get the system running and so we mounted our temp sensors onto the lines these are k-type temp sensors that have electrical tape on them so you could use that version or the clamp version and we also need to go inside the building and make sure we have a clean air filter and then also check the airflow to make sure we have the proper amount for the size unit we have and we need to determine what type of metering device we have in this case we have a thermostatic expansion valve so we're going to be checking the refrigerant charge using the sub coin method before we connect our hoses to the system we just want to make sure to have these hoses snug on the manifold we want to make sure that i have the handles closed and we're going to go ahead and connect in as well i have the manual load loss valve in the off position right now and so we're gonna connect our high side this is our red hose on our small liquid line and we're gonna connect our blue hose on our large vapor line you shouldn't have any refrigerant squirting out if you have new rubber grommets in these hose ends right here so you gotta replace them every once in a while now that we have refrigerant pressure in our hoses we need to purge the air out of this hose right here and since our pressures are equalized we're going to open both handles at the same time and we're going to force the air out of this hose if these were not equalized we'd open one handle at a time the blue handle first and close it and then the red handle first and then close it in order to purge our air so now we have all of the air purged out and there's just refrigerant in this surface hose this is the hose that we're going to connect over to the refrigerant bottle over here now we're going to connect our hose onto the bottle we're going to make sure that this valve remains in the off position i want to make sure to have this refrigerant bottle upside down because r410a has to come out of the bottle as a liquid even though we're going to be charging it into the low pressure side which is vapor and so right now this this is still shot so we're going to open this up we're going to purge the small amount of air out down here and with these handles shut you got to make sure that these are shut first so they're both shut then we're going to open up our tank after that we can zero out our scale so we're in pounds right now i'm going to change it over to ounces and make sure it's zeroed out so you're going to see it fluctuating a little bit because this tank the liquid inside is still sloshing around as well we'll turn our temp meter on hopefully you can see that and we're going to be charging right over here while the system's running but first we want to turn this system on and let it run for about five minutes uh before checking the refrigerant charge we have the indoor air running and now we're going to push our electrical disconnect in and start this unit up so here we're measuring our high side pressure and here we're measuring our low side pressure so this is our vapor line which is on our large large tube and so we would check our total superheat with these two right here with our temperature here and our pressure here we're going to be checking mainly sub cooling between here and here and that's because we have a thermostatic expansion valve if we had a fixed orifice we would be mainly over on these two and checking our total super heat so we got to let this system run for about say five minutes when you have a txv the other thing that we want to monitor is we take our pressure on our outer ring on the vapor gauge and we bring that into the pink inner ring that's r4 tonight saturated temperature in the middle of the indoor coil we want to make sure that that does not drop down below 32 degrees and you see right now it's about say 34 degrees if it was below 32 degrees any humidity that's in the air crossing the indoor coil would freeze onto that coil and eventually turn it into a soft block of ice and so if we were down at 32 degrees we may be extremely low on refrigerant or there could be a liquid line restriction problem or a low airflow problem and you can check out other videos that we have on that so i'm gonna let this system run and then we're gonna come back so now it's been about five minutes and on our liquid line we measure a temperature of about 77 degrees and if we were to measure our pressure on that high side line in order to determine our sub cooling we have about 220cm psi we bring that into the r4 tonight saturated in a ring and we have about 77 degrees so 77 minus 77 and we have zero degrees of sub cooling however up on the outdoor unit reading plate this unit calls for 9.7 degrees as a target sub coil so what should happen is this should be higher and this should be lower to give us a spread of about 9.7 or 10 degrees of sub cooling now let's also just check our uh superheat our total superheat and so we have 50 let's call that 59 degrees and if we measure our pressure on our large vapor line we measure about uh 110 psi or 109 we bring that into the saturated temperature inner ring and we have 35 degrees there's a r410a saturated temperature in the middle of the indoor coil so we take say 58 minus 35 and we have 23 degrees of superheat so that's of total superheat because we're measuring it at the outdoor unit now a txv should be able to handle a superheat of about say 8 to 14 degrees across that indoor coil so what this is telling us is we have no sub coin which means that we do not have liquid only heading to the txv so we have a little bit of vapor and liquid heading to the txv so we need to add refrigerant to this system so we're gonna add a little bit at a time into our low side line so we do have liquid exiting the tank and it's coming through this yellow surface hose into the manifold and every time we open this gauge handle up we're adding our for tonight into the low side which is the vapor line now that vapor line is heading right to the compressor so you could add a vaporizer here or at the tank which would change that liquid to a vapor instead what we're doing is we're metering it a little at a time with our handle right here and so you see that we have one ounce that the the scale is monitoring the loss of refrigerant weight in the tank and we see one ounce so far we're going to keep adding refrigerant we know we have no sub cooling so we know we're very low on refrigerant if you were to just open this handle up and allow liquid to slug that compressor that could permanently damage that compressor and therefore you're not going to be having any air conditioning so you don't want to do that so you just want to meter a little at a time so you allow a flashing of the liquid into saturated or into vapor before that refrigerant enters that vapor compressor in this case we have a scroll compressor in that outdoor unit now that we added refrigerant in i'm going to check our sub cooling and we have 78 degrees on our liquid line and if we checked our pressure we converted it to the saturated temperature for r410a it looks like we have about 79 degrees so we take 79 minus 78 and we have about one degree of sub cooling however you should let the the system run for maybe three four minutes before checking the charge again after you add that refrigerant but i do know that we're very low on refrigerant because i was the one that recovered the refrigerant out of here if you leaked that much refrigerant you really need to find the leak before just charging all that refrigerant back in because what's going to happen is it may just leak right out the next day and so it's not doing the customer any good if we're just adding all that refrigerant back in if it's a little low then that's one thing but if it's severely low we want to be searching for that refrigerantly you know it could have been that the uh prior technician just did not know how to charge the system so it could have just been low on refrigerant just from that prior technician so if it's the first time that you're arriving at the site you're kind of trying to do some detective work in order to determine why you're a little low on refrigerant so we got 10 ounces in so far so i'm gonna go to about three quarters of a pound which is about 12 ounces and then we're gonna wait a few minutes and check the charge again i'm going to pause right here and give the refrigerant a chance to cycle through the system and then we're going to check the refrigerant charge again remember that when you're adding refrigerant in the field don't add it necessarily this quick i am doing it a little quicker just for the sake of the video but you want to add it slower and then check the refrigerant charge again you just want to make sure to not over charge the air conditioning system so it's been about five minutes so far and if we were to look at the saturated temperature of r410a in the inner ring on the high side gauge we have a little bit above 80 so maybe 80.5 and over here on the liquid line we have 80 degrees so we have maybe like half a degree like one or half the degree of sub cooling right now and that's after adding 13 ounces so that means that this system was really really low on refrigerant let's also check the total superheat and so on the vapor line we're measuring 53 so 53 minus 38 and so we have about 15 degrees of total superheat so what has happened here is all that refrigerant that we added in did not end up in the outdoor coil yet uh what's happened is we've added the refrigerant in and now the txv has a solid column of liquid heading to it so now we have fully liquid heading into it and the txv is letting more refrigerant into that indoor coil which means our total superheat is lowering down so all the refrigerant we just added in is basically running in that indoor coil presently so now that our our total superheat is closer to being accurate our sub coin should increase as we add refrigerant so what's really happening is as we add the refrigerant if our total superheat is correct what's going to happen is the the refrigerant traveling through that outdoor coil once it turns into a completely liquid state it's going to make more passes through the tubing which is going to allow it to lower in temperature and that's how we get our subpoint so in that outer coil it starts off coming off of the compressor as a high pressure high temperature discharge gas it's the hottest and highest pressure uh in the whole system and then it goes into that outdoor coil and then what happens is it lowers in temperature until the refrigerant becomes saturated where liquid and vapor both exist in the middle of that of that coil and basically the refrigerant holds the temperature steady as it phase changes basically from a vapor to a fully liquid state and then once it gets down say to the lower part of this coil it's in the fully liquid state makes more pass through the coil as air is crossing that coil and it lowers the temperature and so that's how we get our our sub cooling which is the the lowering of the temperature of the liquid refrigerant that's the basically the definition of sub cooling and the definition for total superheat is the increase in temperature of the vapor refrigerant and so you always want to remember that even though we're measuring total superheat out here it's actually happening at the indoor coil and we're measuring sub point here and that's happening at the outer coil so we have 20.8 ounces in so far and once again you would not be adding refrigerant this quickly in the field i know how much i pulled out of this system and so i just want to show you what it looks like as we're doing it but i'm going to stop right there we're at 22.4 ounces and i'm going to give the refrigerant a chance to cycle through the system but if we were to look at our sub coin right now just say uh our r410a saturated temperature is about 84 degrees so 84 minus 79 and a half and we have four and a half degrees of sub coin so our sub point is increasing because our sat temp is rising and uh this is rising as well but eventually it's going to be a spread between the two and we'll have a higher sub coin so i'm going to let this sit for about another four or five minutes and then we'll come back to it again it's been about four or five minutes so far and we take our pressure we bring it into the saturated inner ring for our four to nine we have about 84 degrees 84 minus 78 we have about six degrees of sub cool and we need to be within plus or minus three degrees of our target up on the rating plate but i like to be about say one degree higher than our target sub coin and let's also check our super heat um that shouldn't have changed so that should be pretty close to where it was before so we have 37 degrees as our saturated temperature here we have 52 here and so we have about 15 degrees of total superheat so that's about right that's what the txt should be holding maybe about say 8 to 14 it's just a hair high but uh now we're gonna add a little bit more refrigerant into this so i'm gonna start monitoring this a little closer now and anytime that you're adding a large amount of refrigerant the other thing that you can do is if you don't see the system reacting like like it should say with the sub coin increasing what you may want to do is turn the outdoor unit off and then let the indoor fan continue to run and then basically let the pressures equalize and then turn that outdoor unit back on and when you do that when you add a lot of refrigerant you may have to do that in order to actually see the sub cooling in the in the total superheat change [Music] so we are at about 85 degrees saturated temperature and 77 and a half so we got about about 7.5 degrees of sub coin presently i'm going to keep adding some more at some point here what i'm going to do is i'm going to actually shut off this this hose right here and try to empty this this yellow hose of liquid once we get a little closer to our charge level so we're at about 86 and 77.4 we are getting close remember that the only reason that we're measuring pressure on air conditioning systems is literally to convert it to saturated temperature so that's really all you're looking for is the saturated temperatures and the line temps not necessarily the pressures people ask hey what are the normal operating pressures for our r22 and r410a and basically you know it's a large range you know say it's 32 to 55 degrees is a saturated temperature and so they're looking for this range but it doesn't help you in order to set the charge accurately you need to check the total superheat and the sub cool i'm going to give this a few minutes and then i'll check the refrigerant charge again it's been about four or five minutes again and so so we have our our pressure on our outer ring converted to our saturated temperature for r410a is 87 degrees we take 87 minus about 78 and we have about 9 degrees of sub cooling so at this point right now i'm going to shut this this right here and i'm just going to charge a liquid that's in this hose and that's it so this way when we disconnect from the bottle all we'll have left in here is vapor at the same pressure that's in the blue hose which is on the large vapor line so that's that so it's been about a minute of run time now since we charged the refrigerant that was in this yellow hose into the system and so now we have a saturated temperature over here of 87 degrees and we still have a temperature on the line of 77 and a half and so we have about 9.5 degrees of sub cooling what i'm going to do now is i'm going to shut this valve right here and i've disconnected this so now we have our our liquid line right here this one's full of liquid as well so we're going to charge that into the vapor line and so we want to make sure that this handle over here at the tank is still shut and what we can do since this is disconnected we can open up this handle it's going to allow the liquid refrigerant that's in the side over to here and then we can charge it in a little at a time and so we're not going to be able to check sub coin now but we know that we're basically right at about where we need to be so we should be about 10 degrees of sub cooling presently [Music] and that's it so this system up on the reading plate has about 7.25 pounds of refrigerant total included with the 15 foot with a line set and so we added in 37.8 ounces so that's quite a bit all right now i'm going to shut this handle over here and as soon as we disconnect here you want to put the cap back on because you don't want humidity condensing onto the inside of that port [Music] in this case i'm just going to put the regular uh port cap on but if it's in an accessible area where these uh ports are located at you have to put locking caps on them uh but that's it so in our gauge right now in our hoses we just have vapor refrigerant and so that can be vented and we don't have any liquid in there so that's that's good so that files at the minimus rule and so that's how you do it make sure that your tank handle right here is off before you disconnect this and so now we're good if you want to learn more about the subject of refrigerant charging or troubleshooting make sure to check out our book the refrigerant charging and service procedures for air conditioning so we have full chapters on charging and recovery we've got checking and refrigerant charge we've got service valves we've got pressures and temperatures we also have troubleshooting of air conditioning systems and systems that are poorly designed and basically what you're gonna do about that troubleshooting low airflow problems so there's a lot to learn and check out so we have the full outline over at acservicetech.com and we also have our quick reference polystyrene cards they hold up really well you can throw them right in your service bag and you can use them right right here when you're charging and troubleshooting so we have both of these products available over at ac surfacetic.com and we also have them over on amazon hope you enjoyed yourself we'll see you next time at ac service tech channel

Channel: AC Service Tech LLC

Views: 153,860

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, r410a, r-410a, 410a, r-22, r22, 22, yellow jacket, scale, weight, weigh, st4, temperature, pressure, operating pressures, r410a operating pressure, r410a running pressure, conect, disconnect, purge air, manifold gauges, hvac classes, hvac course, hvac school, hvac training

Id: 9l3n7yQ_N5k

Length: 20min 44sec (1244 seconds)

Published: Sat Sep 11 2021