20 Degree split

[Anthony49]

I am A new tech and after charging a system the way I was taught in school. I went and checked the tempature at the supply and at the return and I was looking for a 20 degree differential. However, it was only 12. Supply 71 and Return 83. After researching this forum I found that if it is above 20 it is an indication there is poor or low air flow. Dose anyone have experience as to what would cause the the differential to be below the 15-20,
that I should be getting. Thanks in advance.


Anthony49

[iraqveteran]

20 split across the coil.....


with that being said. Get 14 more posts and get your pro status...


There is a wealth of knowledge in the Pro forums. These tech details we cannot discuss here in the open forums. Too many DIYers with wandering eyes.


Get Pro. And we can help you out more than you know. Good luck and get postin. See ya on the flip side.

[beenthere]

A. Was that at the supply and return of the air handler, or at registers.
B. How did school teach you to charge.
C. Is it a fix metering device, or TXV system.
D. What was the indoor wet bulb, what was the out door dry bulb.
E. Did you verify air flow.
F.What was it in CFM.
G. What size is the system.
H. Why do some guys ask so many questions, when they were only asked one. :)

[BaldLoonie]

If a sauna, 12 over the coil may be OK. If dry and cool, NOT!

And yes, we normally don't talk technical here so work on getting your pro status.

[snewman24]

These tech details we cannot discuss here in the open forums. Too many DIYers with wandering eyes.


I've always found it interesting how some people interpret the forum rules:

2. Do-It-Yourselfers - not here.

This site is for industry professionals and folks seeking HVAC/R advice and knowledge. Please do not ask for step by step instructions on purchasing, installing or repairing your own HVAC equipment, that is our job and our livelihood. We are generous, but not to a fault.

Questions of this type will not be answered and may be deleted.

[cnpro18]

How did they teach you to charge a system in school?
Was the unit flat?
New system?
Metering Device?
What type refrigerant?
12 degrees....not good....something's wrong.

[Dallas Duster]

I am A new tech and after charging a system the way I was taught in school. I went and checked the tempature at the supply and at the return and I was looking for a 20 degree differential. However, it was only 12. Supply 71 and Return 83. After researching this forum I found that if it is above 20 it is an indication there is poor or low air flow. Dose anyone have experience as to what would cause the the differential to be below the 15-20,
that I should be getting. Thanks in advance.


Anthony49

Keep answering and asking questions don`t let these guys scare you . Do a search I am sure there is alot of info in the regular area`s. Besides you have to get that post count up somehow. The pro section only has so much info questions like yours gets asked in there too.

[sir fix alot]

i smell home owner looking for advice, or tech. that need's to go back to the school he went to and get a re-fund. or i could be wrong:D

[thandar56]

Keep answering and asking questions don`t let these guys scare you . Do a search I am sure there is alot of info in the regular area`s. Besides you have to get that post count up somehow. The pro section only has so much info questions like yours gets asked in there too.

check the air flow and pressures it might be low on refrigerant or a leak

[Anthony49]

We all go to school to learn some instructors are better than others if you were only taught one way, chances are that all you know until you learn differently. I am only here to learn more than I already know, My current book Refrigeration & Air Condition Technology 5th Edition, Nor my instructor felt the need to cover this in any more detail than the fact that the Air Condition were designed to produce a tempature difference of 18 to 20 degree difference across the evaporator when the system is operating. Return air is 20 degrees warmer than the supply air. The Supply air is about 10 degrees warmer than the evaporator metal and the evaroporator metal fins are about 10 degrees warmer than the refrigerant. the refrigent is always the coldest.

Instead of me asking for a refund why not help me be a better tech, I have read the book and have searched this forum for answer. My only question was why and what would cause it to go below 18 Degrees.

As for charging a I was taught to charge it to 68.5 psi on the low side this was a 3 ton unit, R-22, fixed device. the tempature was at the return register and the supply resigeter. Only dry bulb tempature was taken.

[Tiger93rsl]

How did they teach you to charge a system in school?
Was the unit flat?
New system?
Metering Device?
What type refrigerant?
12 degrees....not good....something's wrong.

suction like beer can cold man:D

[cmajerus]

As for charging a I was taught to charge it to 68.5 psi on the low side this was a 3 ton unit, R-22, fixed device. the tempature was at the return register and the supply resigeter. Only dry bulb tempature was taken.

don't go by what you learned at school then, all kinds of factors go into what you get for a suction side reading, the way to charge a system properly is with pressures and line temps. You may have the charge wrong, or airflow, its hard to tell without all your readings. 12 degree differential may or may not be ok where you took the readings, the 20 degree split should be at the equipment not on total duct system. Like others have said get your post count up and apply for pro status to get some more technical advice. DO you work for someone that can help you learn the proper techniques of diagnosing systems or are you trying to work on your own right out of school?(not recommended)

[captain73703]

i 16-22 is a good split and over 23-? air flow problems that in you book. u are most like low on charge. i have the 5th ed too. there is more than enough info there. are you sweating back at you suc valve? is your liquid line warm? not hot warm.

[BigJon3475]

I may get blasted for this but I don't think it get's to technical....this was a reply to a test we had to take for work that had a question with the answer being 20* split....:rolleyes:

"Cooling coils are rated with what is known as sensible heat ratio. This basically tells you the amount of heat the coil will remove which can be verified with a dry bulb thermometer.

Cooling coils are responsible for removing more than just sensible heat. They also remove latent heat which would have to be measured with a wet bulb thermometer. When you know the SHR you also the know the latent heat ratio or latent load.

example: SHR for a cooling coil is .75.

That means that 75% of the capacity of the coil is sensible heat and 25% is latent heat.

You may ask why this is important. Typically when your verifying capacity on a HVAC system you would need three measurement the dry bulb and wet bulb and airflow so you could plot the enthalpy change (total heat removal) so capacity can be calculated.

Sometimes you might hear you should have a 20 degree delta T or temperature difference for the system to be operating correctly. This can lead to problems. Cooling coils remove the moisture first...the higher the moisture content the less SHR and more latent heat is removed. So if you walk up to an A/C system on a hot/humid day use a dry bulb thermometer or what you would think as a normal thermometer you will only be detecting 1 of the two heats removed. Since A/C's remove the latent heat first that dry bulb temp. difference across the cooling coil will be lower than what you would expect because of the large latent load.

How can this lead to problems:
You walk up and take DB delta T (temp. across cooling coil) and you get 15*F difference. The person looking at this system may think something is wrong with the system when in fact it is operating normally it just has a large latent load. Which can be verified with a hygrometer or wet bulb thermometer. If the person checking the A/C checks just dry bulb delta T and see 15* he may start trying to fix a problem that isn't there.

This can lead to overcharged systems, setting the fan speed to low, wasted time...ect.
Please don't think in terms of absolute when thinking air conditioning way to many variables to put up one number and call it good.

I hope this helps anyone that might be looking for that magic 20* delta T"

[21degrees]

Making stupid statements like that is not going to help him. You and him need to read the rules.
He needs to get is count up to 15 then apply pro status and then we will help[/SIZE]

[21degrees]

Thandar56, But not that good read the rules IDIOT

[snewman24]

Thandar56, But not that good read the rules IDIOT

Hmmm.......sounds like your response is a clear violation of Rule #1

1. Who Is Welcome Here?

Anyone in the HVAC industry and home or building owners with HVAC/R concerns and other polite and fun people that are willing to contribute.

Feel free to ask any question relating to HVAC, or other topics of general interest except DIY.

At the same time, be polite and respectful in your answers. We welcome questions so please don't be critical of someone's question, or other member's answers.

Any reply that we feel violates this rule will be edited or deleted.

All members must treat other members with respect. Anyone who posts defamatory, insulting or otherwise disrespectful comments towards others in the HVAC industry will find their posts deleted and possibly their posting privileges suspended or revoked.

Any member that becomes belligerent, argumentative, posts smart-ass comments or requires too much attention of the moderators will lose their posting privileges.

[Anthony49]

Sorry, for any rules violation that may have occured. I was sent on this call becaused the unit had frozen up I was sure it was a dirty A coil or a leak some where in which I had to find. I had a nitrogen bottle, a electronic leak detector and some bubble soap so I had the ability to find the leak but it would take time. I found the leak after it had defrosted at the low side Schrader valve, I replaced both low side and high side and began to charge.
I always check the temp at the supply register before leaving I was not satifyed so I took a reading at the return and my split was only 12 degrees. Thanks to all who may have given me me advice as to what may have caused this I will talk to our senior tech an see what he thinks.

[21degrees]

I was not trying to insult him just trying to help him out. I hire people like this day in and day out and some times gets the best of me. You tell them and tell them but they never change. Oh by the way Did I miss you post to him about no DIYs and step by step information.

[gonekuku]

Those Who Can, Do; Those Who Can't, Teach HVAC. Those who can't teach HVAC are coaches.

[BigJon3475]

Those Who Can, Do; Those Who Can't, Teach HVAC. Those who can't teach HVAC are coaches.


Do what?

[BigJon3475]

I may get blasted for this but I don't think it get's to technical....this was a reply to a test we had to take for work that had a question with the answer being 20* split....:rolleyes:

"Cooling coils are rated with what is known as sensible heat ratio. This basically tells you the amount of heat the coil will remove which can be verified with a dry bulb thermometer.

Cooling coils are responsible for removing more than just sensible heat. They also remove latent heat which would have to be measured with a wet bulb thermometer. When you know the SHR you also the know the latent heat ratio or latent load.

example: SHR for a cooling coil is .75.

That means that 75% of the capacity of the coil is sensible heat and 25% is latent heat.

You may ask why this is important. Typically when your verifying capacity on a HVAC system you would need three measurement the dry bulb and wet bulb and airflow so you could plot the enthalpy change (total heat removal) so capacity can be calculated.

Sometimes you might hear you should have a 20 degree delta T or temperature difference for the system to be operating correctly. This can lead to problems. Cooling coils remove the moisture first...the higher the moisture content the less SHR and more latent heat is removed. So if you walk up to an A/C system on a hot/humid day use a dry bulb thermometer or what you would think as a normal thermometer you will only be detecting 1 of the two heats removed. Since A/C's remove the latent heat first that dry bulb temp. difference across the cooling coil will be lower than what you would expect because of the large latent load.

How can this lead to problems:
You walk up and take DB delta T (temp. across cooling coil) and you get 15*F difference. The person looking at this system may think something is wrong with the system when in fact it is operating normally it just has a large latent load. Which can be verified with a hygrometer or wet bulb thermometer. If the person checking the A/C checks just dry bulb delta T and see 15* he may start trying to fix a problem that isn't there.

This can lead to overcharged systems, setting the fan speed to low, wasted time...ect.
Please don't think in terms of absolute when thinking air conditioning way to many variables to put up one number and call it good.

I hope this helps anyone that might be looking for that magic 20* delta T"


Is this a decent reply that the average Joe would understand?

[BigJon3475]

Those Who Can, Do; Those Who Can't, Teach HVAC. Those who can't teach HVAC are coaches.


NM I think I took your response offensively like teachers can't do the job....I see the other side now. Those who can't do the job anymore teach newer batches?

[Anthony49]

21 Degrees
I hire people like this day in and day out and some times gets the best of me.
Not to be personal but with an attitude such as yours it only make sense that you would not be able to keep anybody. Beside if everybody was as smart as you, then you would not have a JOB. You did Know everything when you started and still don't, so lighten up.

[BigJon3475]

21 Degrees
I hire people like this day in and day out and some times gets the best of me.
Not to be personal but with an attitude such as yours it only make sense that you would not be able to keep anybody. Beside if everybody was as smart as you, then you would not have a JOB. You did Know everything when you started and still don't, so lighten up.

He means good. He is trying to preserve the board. No harm in that. Lot's of people that really wish to totally ignore the rules....sometimes they aren't 100% clear....in terms of peoples opinions of course.

[beenthere]

I always check the temp at the supply register before leaving I was not satisfied so I took a reading at the return and my split was only 12 degrees.

Temps at the supply and return registers are not reliable. The return could be drawing basement, or attic air, depending where the air handler is located. Which will throw your readings off. Along with attic temps being able to influence the supply temp also.

Charging till the vapor line is 68.5PSIG or some other arbitrary pressure isn't proper, or close to getting the charge right.

Study up on superheat and subcooliing.

After you get your post count up to 15, apply for pro membership.
Once accepted, you can ask questions in the pro tech forum. Which is where we can explain in detail.

[21degrees]

21 Degrees
I hire people like this day in and day out and some times gets the best of me.
Not to be personal but with an attitude such as yours it only make sense that you would not be able to keep anybody. Beside if everybody was as smart as you, then you would not have a JOB. You did Know everything when you started and still don't, so lighten up.


Anthony9 who said anything about me being able to keep the people I want. I have had peoplework for me for 3 years. I never ask for life commitments. People like you come and go more often though. To busy talking when they should be listening. Sounds like you slept through schooling and must have been asleep when you reading the rules. No step by step directions in open forum. Ask you boss for help. Don't be shy your mother wasn't!:eek:

[beenthere]

Lets leave Mothers and Wives out of it.

[21degrees]

I am just joking arround and if they can dish it out, better take it.
Yah Just getting tired. Working on proposals for 3 jobs. Can't find any new techs or good kids. 1 guy wants me to send him a contract and wants $30.00 per hour and no tickets.Wants me to list hours of work and what benifits he gets. Told him to look else where for work and then he decides to change mind. Games people play!

[beenthere]

You might want to read the post by the "Admin" in the thread, " I helped a DIY today"

I believe its on the last page.

[thandar56]

Please click one of the Quick Reply icons in the posts above to activate Quick Reply.sorry my bad i will keep my mouth shut

[iraqveteran]

I've always found it interesting how some people interpret the forum rules:

2. Do-It-Yourselfers - not here.

This site is for industry professionals and folks seeking HVAC/R advice and knowledge. Please do not ask for step by step instructions on purchasing, installing or repairing your own HVAC equipment, that is our job and our livelihood. We are generous, but not to a fault.

Questions of this type will not be answered and may be deleted.

huh? What are you implying here man?

[snewman24]

huh? What are you implying here man?

What I'm saying is the rule doesn't prohibit technical discussions on HVAC principles as long as you're not giving "step by step instructions on purchasing, installing or repairing your own HVAC equipment". At least that's literally what the rule says. If ADMIN doesn't want any technical discussions with non-pros then they need to modify the rule and make it clearer. Some members have a very broad definition and like to use it as a club against newbies.

[iraqveteran]

I see what your sayin.

I try to avoid going technical in the open forums. There just too many DIY and engineers out there that figure they know what they are doing.

Not to mention, if we start helping out everyone that claims to be a tech, then whats the point of the pro status?

I see it this way. If we press on the issue of the member to get professional status, then we are doing 2 things at once. First off, we are weeding out the non-pros that are trying to get free diagnostic help. And second, once they apply for pro, and get pro status, then we know that they are a pro.

And then once they move into the pro forums, the wealth of knowledge is overwhelming at first. But definately worth the time waiting.

[21degrees]

I am not trying to be rude. But we do need to look after our lively hood. Cause if I have to go back to drive through window, I don't know if my mind can take it.:eek:

[Dallas Duster]

The lively hood will always be there, the refrigeration system has been around for awhile now . It takes a certain type of people to understand it and respect it. If a homeowner is asking questions he won`t stick around here for very long. Not every tech thinks the same and good-one are getting hard to find. So regardless of what classes they go to some people can`t make it stick or comprehend basics. Some people call it job security.

[21degrees]

Yah thats what they said about the american dream to. World is changing faster than you think. Business practices are changed monthly.

[beenthere]

Please click one of the Quick Reply icons in the posts above to activate Quick Reply.sorry my bad i will keep my mouth shut
I was talking to 21.

[Dallas Duster]

What is Canadian dream? It is an ever changing world it is now known as a global economy.

[21degrees]

What is Canadian dream? It is an ever changing world it is now known as a global economy.

I have been on 2 vacations this year 3rd one coming in August. Go to lake lot every weekend, Bills are getting paid. Money in bank. Have 6 newwer trucks oldest is 2004. Paid cash for last 2( brand new 2008 and 4k miles on 2007)Move into a bigger shop this year. Live in a 2200 sq' house that has just about been totaly restored. Just been awarded some nice jobs. Beer and smokes taste a hell of lot better. That is the Canadian Dream. By the way I was not insulting the United States. I am just pointig out that you cannot take things for granted these days. Tommorow I could be stuck woking out of town like I did not so long ago.

[Dallas Duster]

Well to me it sounds like your dream has come true ,my goal is somewhat similar to make more and work less.