Charging using Subcool

How to check the refrigerant level of your car's air conditioner using the subcool method. Newer cars use a thermal expansive valve (TXV) instead of an oriface tube, which can make it really easy to overcharge the system using those recharge kits with the gauge. When removing refrigerant, purge it through the yellow hose in the center of the gauge and bleed slowly from the low pressure side. DO NOT stick ANYTHING in to the schrader valves in the service port. and DO NOT vent from the high side or you can seriously HURT yourself.

[@joseramonherreramendoza9260]

You know that this is the only video that made me fully understand subcooling and superheat ☝️🤣🤣🤣🤣😎😎😎😎😎... thank you... great job...

[@MsLincos]

Same here!😂

[@waltdembeck4634]

My kind of guy - "throw the can gauge in the garbage" love it! Don't forget to throw out the stop leak also.

[@encoremaintenancepartners9499]

That’s how it works. Good job. Good visual aid. I good Delta T is certainly between 37-43 degrees

[@EmilyAndClark]

Really excellent video. I have developed a marine refrigeration system. It's going into production this month in kit form so I need to do some videos. Yours is the best I've seen on charging an expansion valve system. Good work.

[@ahmedalmuhandir9733]

Thanks very much for your easy explanation if you can make screen shot for that drawing that will helpful for so many people

[@c.k.matthews365]

best explanation I've found, thank you!!

[@MsLincos]

Thank you for this video and all the answers you give. Learned a lot!🙂

[@Sals_Garage]

This is a really informative video. Thank you for sharing 🙏

[@pingpong9656]

You are my kind of TEACHER... infarct you are a GURU!

[@Mihai1174]

exelent ,i always look for low and high presure on gauge and touch the low line with hand,or sometimes the high pressure freeze when starving freon

[@WV591]

The one and only charging instruction that explains the inner gauge reading and not the same old stuff. TU all the way. it is strange, I tried this on two different cars and two different temperature gauges. and I can never get a reading of less than 85-90 degrees on low side line/evaporator superheat and yet both AC systems work and blow cold Air down to 42 degree.

[@Chaddz3]

I am betting with that high of a superheat reading, the compressor is short cycling like crazy. The reason you are still getting the low temps out of the vents is because the first 1/4 to 1/3 of the evaporator is probably around 20-25*F and the other side is near the temp of the inside of the car and the temps are equalizing there as they blow out of the vent. If you have very low humidity you will see this, however if the humidity is really high, the side of the evaporator that has the boiling refrigerant in it will freeze up and have a big chunk of ice form on it blocking airflow though the evaporator, which will make the air start blowing warm or hot.

[@dougswanson9142]

I just had this same problem, low side temp reading over 80 degrees with a known good charge in the system. The reason in my case was the high temperature in the engine compartment was affecting the accuracy of the low side temp probe reading. I used some pipe insulation over the taped on temp probe and got a more accurate low side temp reading. Low side evaporator tube in my car is near the engine exhaust manifold so very warm in the region of the temp probe and why it needed the added insulation.

[@khyberafridijamrud]

Great video.

[@polaris199pt]

Very clear. Thank you

[@athersheheryar689]

thanks

[@needleonthevinyl]

This video is great. Refrigeration theory is not well understood in the automotive world.

[@billspooks]

This video is really helpful however I still have one question. What rpm should the engine be at? Should it be at "idle" or should it be something higher like 1,000 or even 2,000 RPM or perhaps does it not matter because it all comes out in the wash since we are looking to have subcooling and superheat match closely around 20 degrees...???

[@pingpong9656]

Does the 20 degree of subcooling stay the same on a hot or cold day? Does ambient temperature affect subcooling?

[@privateparty4900]

It feels like you should account for RPMs other than idle. I don't know if it's right or wrong but I when I do my cars, I put in enough charge that the compressor doesn't cycle due to low system pressure at a highway cruise RPM.

[@martinflores4304]

How can I get my trucks sub cool and sub heating? I have a 2015 Chevy Silverado 1500 5.3

[@issamadam9352]

Again if this applicable for AC with IHX or not?Thank you

[@mr_mnky]

Do you take these readings when the compressor is on, off, or take some kind of average between the two?

[@scottcrowley2061]

nice

[@shorn77777]

Excellent explanation mate, could you say, if I overcharged the lines, will anything explode

[@Chaddz3]

As a general rule, no. the pressure inside the cans you use to recharge the system aren't high enough to burst the lines in the system. HOWEVER, never open the high side (red handle) on your gauge set when the engine and compressor are running with a can of refrigerant attached while recharging, the can WILL explode if you do. Pretty much all newer cars have a high side pressure safety switch (usually on the compressor) that kicks the compressor off if the pressure gets too high. That being said, whenever you work with the A/C always make sure you are wearing rubber lined gloves and eye protection. If liquid refrigerant hits your skin, it'll freeze almost instantly and cause frostbite, not to mention it hurts like hell. Gloves will slow the cooling effect long enough to hopefully pull the gloves off before it freezes your skin. If liquid refrigerant hits you in the eyes, it will freeze your eyes instantly causing permanent blindness. Be safe!! The biggest danger with overcharging your AC is dropping the superheat too low (which means refrigerant entering the suction line between the evaporator and compressor is still in a boiling state and partially still liquid). If liquid refrigerant gets inside the compressor, it can break the compressor internally because liquids do not compress.

[@RC-Heli835]

I wonder if you can use superheat to check fixed orifice systems also? I don't see why not. sometimes pressures can be very misleading for different reasons. For instance a weak compressor might cause someone to keep adding freon to a system trying to get pressures up to 35 while all along have more than 2.45 times the amount of freon that the system calls for. I worked on a system like that yesterday and did add 2 cans to it trying to get pressures up. Finally got it up to 33 and 200 but it did nothing for the cooling with vent temps averaging 66 to 80. Now the system has been evacutated, vacuumed down and recharged to 3.5 lbs and the pressures were 15 low and 110 hi. I can only assume the compressor is failing from having too much freon. This system never cooled right after the compressor was replaced before that it would freeze you out.

[@Chaddz3]

Yes this will work on fixed oriface too but it the logic is a bit different. Refrigerant charge will affect both subcool and superheat at the same time. In your case I'd start with basic compressor troubleshooting. Sounds like a weak compressor. Also verify that your orafice tube isn't plugged up.

[@devonpeeples2188]

Sounds more like a clogged office or filter drier than a failing compressor. The compressor is just there for flow and pressure is a byproduct of the metering device in that flow of refrigerant. A failing compressor will typically have high suction and low liquid pressures. The only compressor failure I could think of in this scenario is if it is coming apart and has again clogged the filter.

[@jharrison6557]

Shouldn't the temp probe for subcooling be on the condenser outlet?

[@stanmanis1]

hey chadd is this procedure the same for a fixed oriface system as used in older cars,numbers calculations etc

[@Chaddz3]

Fixed orafice both the subcool and superheat are affected by refrigerant level so you'll need to watch both. Again you want the system to balance out.

[@issamadam9352]

Great job but my question where you took temp reading from auction line before or after the suction port as it seems in the video before?

[@Chaddz3]

Generally you want to take the temp reading as close to the exit of the evaporator as practical.. The closer the better, however getting to the optimal position may not be easy if there is a bunch of stuff in the way...

[@blaze2051]

@@Chaddz3 what about the condenser ? inlet or outlet on the condenser or before or after the hiside service port before after the sight glass?

[@platinumhvacrtechnologies457]

@@blaze2051 out of the condenser

[@yemiasaolu1622]

How can someone get information about the standard value for superheat and subcooling for various car model and can we say it is the same for all model

[@Chaddz3]

Unfortunately, the automotive industry doesn't make that available. They want you to completely recover evac and charge based on refrigerant weight. The only way to really get the correct actual number is to measure it on a correctly charged system. But the rule of thumb is you want the subcool and superheat numbers to match in order to balance the system.

[@JamesAutoDude]

What about orifice tube vehicles?

[@blaze2051]

i did this method idk if i did it right here are the numbers hi-side sat temp. was 130F(200psi) Line was 110F lowside sat temp was 32F(30psi) Line was 70F . so that means my subcool is 20F and my superheat is 38F. so that means im undercharged that my ac cycles on and off every 30 seconds? even tho my vent temp was 41F on low speed and non circulate air, on a 95F day do cars have a low and hi pressure switch? mine is a honda 2.4L engine

[@scottcrowley2061]

probably

[@metalhalide4043]

When checking pressure/temps what should fan speed be at, recirculate on or off? Do I check the liquid line at receiver inlet or outlet or close to TXV, my receiver is mounted on condenser and there is a few feet of line to TVX which may lower subcooling. With my fan on low speed I had 48 degrees line temp on evap outlet and 75 degrees on high speed, did not check pressures yet but 75 seems high.

[@Chaddz3]

You want to check your subcool on the liquid line as close to where it exits the condenser as possible.. if your receiver/dryer is integrated into the condenser (the car I used in the video had the receiver dryer on the side of condenser). Usually just in front of the high side service port on the condenser side works great. But gen rule of thumb is to take your reading within 3 to 5 inches of the condenser outlet. Also you will want the AC settings on max AC full cold temp fan at highest setting. Non recirc mode if it will let you turn it off on max AC and both windows down/ and or doors open. If your vent output temp is that high first verify what your saturation temp is in the evaporator. Should be 45F or lower but not below 32F or the evaporator will freeze over. Also be sure that your temp blend door is fully closing and not allowing any hot air from the heater core thru and that there are no leaks in the air box around the evaporator. And it's not pulling air from somewhere other than through the evaporator.. if you mean the superheat is 48 and 75 that is way way to high and either means that the system has no refrigerant hardly at all or the TX valve is stuck closed or the compressor has a problem or youhave a plugged line or possibly a crushed line somewhere

[@Chaddz3]

Also if the super heat is way off like that. With your gauges connected and the system off for at least 1 hour or more both the saturation temps of the condenser and compressor should be nearly the same and also within a couple of degrees of what the outside temp is.. if it way lower, the system is way undercharged. Also once the system starts up verify that the high side pressure is significantly higher than low side.. if the system is on and compressor is running, but low and high pressures are near the same, you have a bad compressor

[@metalhalide4043]

@@Chaddz3 Sorry, I meant 48 and 75 line temp and not superheat, once I get the gauges I will check saturation temp.

[@Chaddz3]

@@metalhalide4043 yes you'll need gauges to see what's going on in the condenser and evap.

[@johnfredette1034]

When checking subcooling, don't you need to have a high velocity fan blowing on the front side of the condensor to remove the heat from the refrigerant? When I check the subcooling on my Toyota Sienna, the sensible temperature of the high side line slowly creeps up causing my subcooling number to continually change (get smaller and smaller, until I have a negative number - which I believe means that the condensor is not getting rid of the heat). I realize that checking cars are a different beast, as compared to checking the HVAC on a house (which has a huge fan that's removing heat at the condensor), so how do vehicle mechanics deal with checking subcooling on a vehicle that's stationary?

[@datsuntoyy]

What I do is mist the condenser with water. Temp will drop sharply then start to rise again as the water evaporates off. At a certain point the temp will stop rising for a short time, usually around 20 seconds then start rising again. Temp below the pause time seems to be the artificially cooled time while after the pause it's undercooled due to not moving. Don't soak the condenser, a LIGHT mist but over the entire condenser. I know this to be half way decent because the pause temp is what I usually get when I have a big fan in it's place. Definately not the most scientific way, but It'll give you a good estimation of the (going down the road airflow) temp.

[@johnfredette5758]

@@datsuntoyy Thank you for your suggestion.

[@tunemymods]

Assuming this is max ac, max fan?

[@tobyfriddle9919]

How did you determine that 20 degrees was the correct superheat??

[@Chaddz3]

There isn't a spec for it that I can find, but all the 2012-2017 Ford focuses (2018's use R1234yf) I have done AC work on seem to have between 20 and 22 deg of superheat when the system is working correctly and giving good vent output temps. Since these are non adjustable TX valve systems the TX valve regulates the SH. From experiment ing with the system, the superheat would always stay at the 20 deg spot unless had the system almost fully discharged or it would start to drop just right before the high pressure safety switch on the compressor would kick it off. The subcool would be the only thing that changed when adjusting the refrigerant charge until it was almost empty or way overcharged. Ñow on my truck, which uses an oriface tube. The SH on that does change with the refrigerant charge. (It also changes depending on blower fan speed, which the SH on the car didn't) For the car I seemed to get the best results with the SH and SC equal, based on vent temps.

[@Chaddz3]

Another interesting note, the factory service manual only gives pressure readings, there is no mention of either subcool or superheat specs.

[@carstensklit491]

Thank you for a great video. Just did a test on my trusty old Citroën (C5 from 2001).. I have the gauge-set, but never touched the filling on the car.. Am i over or under-charged? The performance is not like it should be, i think. Hope to get a guideline :) Tests; Cabin fan - Full speed. Ambient: 23C/73,4F High pressure: 15 bar/217 psi Low pressure: 2,2 bar/31,9 psi Condensor outlet temp.: 33C/91,4F Liquid-line from evap: 17C/62,6F Cabin duct temp: 10C/50F Second attempt; Cabin fan - 75% Ambient: 23C/73,4F High pressure: 15,5 bar/224,8 psi Low pressure: 2,4 bar/34,8 psi Condensor outlet temp.: 33C/91,4F Liquid-line from evap: 21C/69,8F Cabin duct temp: 11C/51,8F Third attempt; (the engine room heats up a little) Cabin fan - Full speed. Ambient: 23C/73,4F High pressure: 16,5 bar/239,3 psi Low pressure: 2,5 bar/36,2 psi Condensor outlet temp.: 35C/95F Liquid-line from evap: 24C/75,2F Cabin duct temp: 13C/55,4F

[@Chaddz3]

What's your static pressures at ambient temp (also include the ambient temp when static pressures are taken... For low 70 deg temp your pressures and subcool number is really high... What's really wonky is how high your superheat is.. you may be overcharged, but something else is going on as well.. possibly a bad TX valve or plugged oriface tube... Your high side pressures are really high considering your ambient temp.. and low side is not bad. But it's getting a bit high on the later attempts.. may also have contaminated refrigerant either with non condensables or moisture... That one i'd wanna evacuate, check the metering device, possibly replace receiver/receiver dryer vaccuum all the way down.. recharge then retest.

[@Chaddz3]

For reference this is where I am now... Ambient. 71 F High side 200 psi Low side 29 psi Condenser outlet 110 F Evap exit line 52 F Cabin vents 43.3 to 43.5 Cabin fan max speed and both vehicle doors open.. With engine at 2500 rpm vent temps drop to 37 deg F. These numbers taken today from my 2001 Ford ranger.

[@Chaddz3]

Ok at 68F your static pressure should be around 67-69 psi.. so it's not far off there. Here's another test to do turn AC on with gauges hooked up allow to run for about 10 minutes and let everything stabilize. Then shut the system off and watch how fast the pressure in the system drops back to static. It should take no more than a minute or two and both high and low should change at same rate and become equal at about the same time. If they take forever or one side changes way faster than other side, you may have a restriction in one of the lines somewhere (usually a plugged oriface tube or stuck TX valve)

[@carstensklit491]

@@Chaddz3 Thanks a lot mate - For some reason I didn't get a notifification on this one :/ I think my TXV is dead. It takes more than 15 minuttes to equal pressure. Again, thnak you for your videos - They are great :)

[@paulthompson1654]

hi 1st automotive should be checked at idle 900rpm and at fast idle 1500rpm 2nd Ideal pressures for R134a at any engine speed . idle or fast rpm ..LOW around 30psi , freezing point is about this temp Ideally High side should read 160psi on a 90deg + day . Condensor size dictates this. Why does it matter ,,lower condensor pressures equals colder refrigerant to evaporater inlet= better performing system on a hot day .

[@joeydelmarsjr.646]

Is there way to diagnose a bad expensive valve / condensor / drier with taking subcool and super heat readings ? My ac keeps short cycling at higher revs but not at idle of 750rpm

[@Chaddz3]

For a bad tx valve, usually those result in a very low low side pressure and excessive high side pressure. Once the system is turned off the pressures take a very long time to equalize. With this your compressor shuts off pretty quick then stays off for a long time before it comes back on.

[@joeydelmarsjr.646]

@@Chaddz3 thank you for the reply. I took it to a AC mechanic and he couldn't tell me whats wrong except that its not working right. so when he had my rev it to 3k its starting to short cycle. he said the low side drop to below 20 and the hi side when up to 350, it would shutoff and after 5-6 secs come back on. hes said it would be condenser or expansion valve or compressor but the compressor workings fine at idle and it blows cold.

[@Chaddz3]

@@joeydelmarsjr.646 I'm gonna lean toward a stuck expansion valve or there's a restriction in a line somewhere. Check your high side lines for any kinks or something that could cause a restriction when engine is being reved you should be able to find a plugged line by looking for a temp drop in the line somewhere. It'll be hot before restriction and cold after it. Has the compressor ever been replaced before? The subcool could be all over the place depending where the restriction is. If it's after the condenser you'll have a very high subcool if it's plugged in condenser or before you may very low or no subcool

[@blaze2051]

@@Chaddz3 i recently replaced the compressor

[@Chaddz3]

@@blaze2051 should be able to evac the system and recharge. Since you replaced the compressor. I would replace the receiver drier too since a blown compressor usually sends its guts into the receiver drier.

[@ahmedalmeer2996]

Hii chadd..... first thank u for this vedio..... from ur vedio i understand that car ac can be charged by balance between subcool & superheat is that right?? Sbcool =superheat ~+_ 2 degree ....... by theway car have txv valve and every txv should chARGED BY SUBCOOL only as i read every where ...... ur method is perfect as i see .... please can u explain to me your refrence in this method ?? Because every technican used only suction presssure as refrence to charging or they used charging by wieght (grams or uonce) ....this is the first time that i see the balnce between sucool and supercharged ... thanks

[@Chaddz3]

Charging by weight is the best way to charge if the system has been completely evaculated and is fully empty. The method I am showing is for systems which still have refrigerant in them and is only low of refrigerant. All systems will lose refrigerant over time through the compressor seal as it doesn't completely seal. If you do have an actual leak, you'll need to repair the leak after evacuating the system which will need to be charged using the weight method. Subcool and Superheat comparison method is used primarily by HVAC techs when recharging central air systems in buildings, where the actual capacity of the system can vary or may not be known. What these other techs are doing with suction pressure alone does work on older oriface tube systems, where the metering device size is fixed and isn't adjusted by the TX valve. Since the TX Valve actually monitors the superheat reading, it will "throttle" the refrigerant based on what the superheat value actually is, in attempt to keep the superheat reading at the proper value, which will make the suction pressure pretty much stay at its specified value unless the system is nearly empty or extremely overcharged, hence suction pressure alone doesn't help you here. For more information look up how the refrigeration cycle works, with the exception of operating pressures, temperatures, and refrigerant types, all refrigeration systems work pretty much on the same basic principles... You can learn more here.... kzbin.info/www/bejne/aGjYdIWHaKdrqJY

[@ahmedalmeer2996]

@@Chaddz3 thanks

[@slava7935]

Great video! Can you verify something for me please. Is it normal for a compressor to never cycle, but rather be on continually? This is a bmw with Seiko Seiki, I believe is a rotary vane compressor. Btw, the cooling in this car has issues.

[@NicholasAndre1]

It depends upon your system setup. My old GMC has a oriface tube, not a TXV so the system cycles the compressor to maintain pressure. The newer cars typically have TXVs or electronically controlled setups and in those cases usually the compressor runs continuously (except of the RPM gets sufficiently high that the pressure switches go out of range). Some vehicles will have a variable output compressor which allows changing the amount of refrigerant compressed in each stroke dynamically which can allow for more uniform cooling conditions and less cycling across a wide range of RPMs.

[@disonesto]

What about adjusting the txv? Almost all cars have a Allen adjustment on the bottom of the expansion valve. It can be turned in and out. Tested it on a junk replaced expansion valve

[@Chaddz3]

You could try adjusting it, but usually those are already preset at the factory and if it's off, it's usually best to just replace it. The only way those get out of adjustment is if the sensing bulb starts loosing refrigerant and changes it's calibration pressure. Or worse yet they start sticking..

[@Scott-eh2xy]

I made an excel sheet for this. Wish I could upload it for someone to check out the equations since I'm a noob at excel.

[@jamescharles7510]

At what rpm do you do this test and how do you set the blower fan and inside or outside air?