The amount of heat removed from a liquid below the boiling point. If your condensing temp is 100 (converted from your high side reading) and your liquid line is 90°, then your subcooling is 10°, typical for a residential system with TXV meter.

baldloonie, you dummed it down too much. Is 10 deg good, bad, OK, or what? If 10 is normal, what does it mean if it is 5? Or if it is 25?

As a comparison, the mfgr provides a chart for me to enter outdoor temp and indoor DB & that intersection yields a number, say 5. Measure the suction pressure & convert to a temperature for the refrigerant in use, say that is 32. Measure the suction line temp, say it reads 70. S.H.=38. Then, this means I need to add refrigerant in order to reduce the Superheat from 32 to 5.
What do I do with a sub-cooling number? Write it in the wind?

For non-TXV equipped evap coils, the system is charged by superheat based on the chart you mentioned. Only txv equipped evap coils are charged by subcooling.

The chart tells you if the number is high, low, or acceptable.
If you now enough to be charging a system you should now how to adjust to get the correct value.

brickeye:
We all love a S.A.!
You could have just skipped the post, for all that was worth!

Sub cooling takes place in the lower third of the condenser. To much sub cooling reduces the condenser surface which raises the head pressure excessivly in warm weather. If you don't know what effect high head pressure has on a system and you work in this trade, you'd better go back and get somemore training and if you're a homeowner/DIYer what you've been told here is all you have to know on the subject and then some. If you feel the need to make snide comments to people like brickeye, who has been helping people in this forum for years, maybe you should go find a little more difficult means of getting the information you request,,,,,,like maybe book!

You know, if the intent of this forum is to help folks & educate, some posters could do a lot more to answer the question asked, instead of acting like a politician and answering a question that wasn't asked. I know it is the number of degrees it is cooled below the condensing temp, as does everyone! How much below should it be? NO, it is NOT in the charts, because Trane didn't put it in the charts for this unit. If that means it is a 'don't care', fine, just say so. If there is information, not just as you say a snide comment such as, "If you now enough to be charging a system you should now how to adjust to get the correct value.", then just don't even bother to post! H *ll, if I knew, I wouldn't be asking the question! Are you really here to assist or to just take a sucker punch?

A simple straight answer was all that was necessary. Maybe that answer should have been, "I don't really know, but you might find it in your local library". But no, don't admit not knowing, just kick the guy for asking as a defensive measure!

When servicing TXV controlled systems, it is always necessary to check both the Super Heat & the Sub Cooling.

Concerning the refrigferant cycle, there are many variables.

The Air-Conditioning Refrigerant Cycle and Rate of Flow Determinants

I am only speaking to this troubleshooting issue to inform consumers of air conditioning systems and uninitiated Techs about the refrigerant cycle in an air-conditioning system.

The sole job of a thermostatic expansion valve (TXV) is to keep the Super Heat near its setting somewhere between usually eight to 12-F super heat. It must have a solid stream of liquid to function properly & at full capacity

Perhaps it is time to talk about how a fully open thermostatic expansion valve can result in high superheat and a very low transfer of heat from the conditioned environment to the outdoors. The uninitiated might believe that a fully open TXV condition could only result in a flooded evaporator coil & zero superheat.

The reason it does not flood the coil with liquid refrigerant is that the compressors volumetric capacity can not supply the condenser with enough vapor to condense to supply a solid stream of liquid to a fully opened thermostatic expansion valve (TXV). Once that cycle begins, it will continue until a cause of the problem is removed.

If the system is low on refrigerant resulting in vapor mixed with a liquid within the liquid line to the evaporator coil, the TXV will open the in its effort to try to keep the eight or 12 Fahrenheit superheat setting.

Then because the TXV is trying to keep its super heat setting the cycle continues to repeat, a too fast rate of refrigerant flowing from the condenser coil resulting in the mixture of vapor with liquid. This results in reduced TXV & DX Coil capacities along with a high superheat flowing back to the compressor. This condition greatly reduces the Btu/hr absorption & transfer of heat from the conditioned space to the outdoors.

The job of the thermostatic expansion valve is to keep the superheat at a setting of say eight, 10, or perhaps 12°F superheat. The rate of flow through the TXV metering device depends upon the heat load that is going through the evaporator coils and fins, as that heat load determines the rate of evaporation and therefore heat absorption of either condensate or sensible heat as it is then sucked back to the compressor.

There are many things that can starve the TXV and the evaporator coils among them are restrictions in the refrigerant line components. When the TXV is not maintaining the desired superheat then we have a problem that needs to be accurately diagnosed in order to reveal the specific causes of the problem.

Of course, we all know that we accomplish this troubleshooting diagnostic procedure by the taking of pressures and temperatures at various points, along with the amp draw of the compressor. In troubleshooting procedures, we use superheat and subcooling procedures as important diagnostic tools for determining the condition and rate of flow of the refrigerant through its cycle. (Fellow Techs, if I have made some misleading statements please correct me in this thread.) udarrell _ 2007

"I know it is the number of degrees it is cooled below the condensing temp, as does everyone!"

- Everyone does not know this. Most people, and some techs, do not know this.

"How much below should it be?"

- This was answered by BaldLoonie who is also a moderator on HVAC-Talk.com.

"A simple straight answer was all that was necessary"

- I believe that you got a fairly simple straight answer from some posters. I try to be straight-forward and with no 'tude. You could always Google "sub-cooling", or ask your question on the site mentioned above.

Good luck.

Thanks to those of you who were helpful, and udarrell was the obvious one, and to the others, have a good life!

jmor, maybe I speak for others too. I have to wonder just why you're asking a question like that in this forum. If you're an (inexperienced) HVAC tech looking for a technical answer just reading a few other posts should make you realize this isn't a peer to peer kind of forum. Also, if you are in the trade and you don't understand that particular aspect of system analyzing maybe its time you learn that decent technicians collect and maintain a personnal library and keep it where thet can reference it whenever they need to. You can't spend your career asking other people what you should already know! Now if you're a homeowner who feels the need to monkey around with their own system for what ever reason, some people here may be of the opinion that you might be treading someplace you really don't belong and contributing to that is something they don't want any part of. If you have a hard time dealing with that its your problem. Free advice is just that and there isn't a soul in this forum who contributes that has to prove their knowledge and background to somebody like you! You have a nice life also. I hope it isn't marred by some tragedy by you sticking you nose where it doesn't belong!

I've probably already forgot more than you know! Pi** off!

MR HAVAC! What a pretentious self adorned title!

Doe you want to help or hinder?

Why did I ask ?

Fascinating subject. Refrigerants are very special substances. They have the ability to absorb or give off large amounts of HEAT energy AS they change states. Change states = changing from a liquid to a vapor and absorbing heat like in the Evaporator. Changing from vapor to a liquid and giving off heat like in the condensing coil. Now I think the easiest way to understand subcooling or superheat is to relate it the change of state of the refrigerant, see the heat that is lost or gained during the change of state of the refrigerant is called LATENT heat, which means it cannot be measured with a thermometer. For instance in the condensing coil the refrigerant gives off its heat, now if we measured with our thermometer the line temp going into and out of the condensing coil it could possibly remain exactly the same, even though the refrigerant has lost a large amount of LATENT heat when it changed state, in this case we would have 0 subcooling. Now try to picture the refrigerant inside the condensing coil as it moves thru and in this case the vapor has all changed to a liquid before it gets to the end of the coil, in this case the measurable temp (that we can measure with our thermometer) will drop since the refrigerant has lost all its LATENT heat it is now loosing Measurable heat in its new state. That is what subcooling is and of course superheat works just the opposite. That is a oversimplified explanation which probably makes little sense, unless you also understand the pressure/temperature relationships of refrigerants a bit also. The signifigance of subcooling is having a column of liquid refrigerant to feed the metering device, without liquid refrigerant at that point your system will not function. The idea is to have enough subcooling to be sure that even under extreme conditions of outdoor/indoor temps etc that there is always a solid column of liquid refrigerant to feed the metering device.

dnt1: I like that.
Thank you.

"I've probably already forgot more than you know!"
OH REALLY?!!! Then how come I'm not the idiot asking the question about sub cooling in this forum and making remarks to the good people responding? If theres anything else about HVAC that "you probably forgot" submit it here and I'll be glad to help you out.
Oh and thats "havac",, supposed to be a little play on words. Do you know what that word means? Do you know how to use a dictionary or did you forget that too?

why is everyone so angry here? My gosh life is to short to be upset about someone typing is some words on the internet. Did you boys grandmother not ever tell you the golden rule? Grannys Quote "If you don't have anything nice to say, it is best to not say anything at all"

You must be on in years dnt1, todays granny says "do unto others, then split" ;-)
Go back to jmors response to brickeye. Totally unnecessary. People like him think they're owed something even though the advice is totally no charge.

ok Mr.havac you got me I am old. Now take a look at this info does any of it appear to be familiar to you? #
# Brenn Tantor
# Dellis Tantor
# Inquisitor (Star Destroyer)
# Tyr Taskeen
# Battlefield Holographic Control Interface
# BHCI
# Beri Tulon
# Sriluur system
# Malcor Brashin
# Graal'diin
# Cattena Squadron
# Tracked Mobile Base
# Government Mound
# Abridon Government Center
# Hamman Flatt
# Lucky Star (frigate)
# Sayan
# Abridon Shipyard
# Abridon Nationalists
# Abridon
# Abridon Government Council
# Abridon capital city
# Sounder Flats
# Sounder Flats computer complex
# Ruul
# Ruul computer complex
# Tantor (Senior)
# Abridon holding camp
# Abridon refugee camp
# Trasse
# Trasse system
# Abridon system
# H7X Ricron Turtle Digger
# Kalaan defectors
# Wehda Jochi
# Gana Lant
# Otome Mapai
# Graaqu Namec
# Belio Phire
# Cancl Rogan
# Javda Tawas
# Spevi Wiwas
# Kalaan prison
# Kalaan
# Kalaanite
# Sarapin drilling platform
# Energy collector
# Kalaan City
# Kalaanite Resistance
# Ruulian mine
# Tulon's task force
# Annihilator 1
# Garryg
# Samiam
# Unco
# Gland
# Mo-die
# Freeze
# Chorizo
# Trasse Proving Grounds
# Ruulian Rebels
# Luke Skywalker
# Remote relay beacon
# Ruul uplink tower
# Battle of Kalaan
# Battle of Ruul
# Sarapin
# Battle of Sarapin (Galactic Civil War)
# Battle of Sarapin
# Eos
# Mission to Endor (Galactic Civil War)
# First Battle of Abridon
# Second Battle of Abridon
# Battle of Abridon
# Escape from Kalaan
# Mission to Ruul (Galactic Civil War)
# Mission to Trasse
# Third Battle of Abridon
# Battle of Hoth
# Battle of Endor
# First Battle of Coruscant (Galactic Civil War)
# Infiltrator (armor)
?????????????????????????????????????????????????????????

eh,,,,well, well, well, well what do we have here.jmor dont worry about it just small stuff above. like virgins in the playground.

fred1944 I'm 58 years old with 3 kids you dumb---! What is this thing with you and virgins anyway? Do you have some kind of fixation about them? Geez I hope you don't live near a school or playground,, I have a feeling a lot of people would not like to know that. Either contribute to the forum or go back to your spelling lessons. BTW I notice an improvement.

"Now take a look at this info does any of it appear to be familiar to you?"
I'm guessing something from star wars type sci fi, correct? Oh except for chorizo, thats a spicy portugese sausage, good stuff too. I'm no spring chicken myself dnt1.

Thanks fred1944! I did recognize that mr.havacc is definitely small stuff, at least in mind. Big ego, peanut brain.
Again, I really do appreciate all, the others of you who are really interested in contributing and helping others.

Put me down all you want jmor but don't forget you come here seeking what I already know. And when you totally screw your system up playing around and trying to be something you're not smart enough to be I'll be right here waiting to marvel at your stupidity again. God I hope your A/C isn't part of a gas heating system. If you play around with that too somebody should warn the whole neighborhood! Stay cool.

mr.havoc
Well, I see that you learn from experience. Your neighbor tells me that he snapped this as you were trying to add Propane to your system as a substitute for Puron. Said you told the fire department, "well, they both start with a "P" & I am "mr.havoc", know what I'm doing and will not share my expert knowledge with you non-experts!!! "Just put out the fire & leave!"

What does all of this garbage have to do with subcoolong?

garyg: Absolutely nothing! I apologize to you and other readers for getting sucked into this word-war by mr.havac's biting comments very early on in this thread.

If I don't know, I ask & generally learn from those willing to answer with a straight answer as opposed to some commentary about not needing to know, you should already know, go get training, read a book, treading where you don't belong, idiot, not smart enough, etc.

On any help type forum there shouldn't be a "dumb question".

Again, I really do appreciate you garyg & all the others of you who are really interested in contributing and helping others & again apologize for wasting anyone's time that might have had it wasted here.

Uploading a picture of a fire!!! Just how big of an idiot are you anyway jmor? I don't have any more time for mental midgets like you. Have your fun. It is highly unlikely you'll get any more assistance from anybody creditable in this forum again. A few more days and you're probably heading back to grammar school anyway!

Don't have any more time????????

Don't kid yourself, you'll be here until you get the last word!

dnt, you posted some good information.

However, (everyone) break it down into a lot of short paragraphs, because most cannot read high density of content. udarrell

jmor,
If you want a professional forum look elsewhere.
This is a homeowners forum.
I have enough degrees and licenses to sink a battleship (or work on one including design) including a PE and a PhD in electrical engineering.
There are any number of sites for professionals wanting advice and help.
If you are to embarrassed to ask there I suggest cracking the books and reading.
In many cases a lot in knowledge can be gained by reviewing the installation instructions for systems.
Most contain exact advice for the system, but the principles can still be learned if you understand the basics.

For the most part, non-pros have been restricted form working on A/C systems for a while now.
Most of the pros here try to provide the type of general advice a homeowner would need to deal with a pro to service equipment without telling anyone to break the law (or giving instructions that would be a violation).

You asked some very basic questions about charging that anyone experienced should now on a homeowners forum.
I get paid to teach classes to professionals.

He's not even worth the time you were courteous enough to give him brick. You're way to good to be dealing with the likes of him.