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Thread: 20 Degree split

  1. #1
    Join Date
    Jul 2007
    Location
    Memphis,Tn
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    8

    Angry 20 Degree split

    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

  2. #2
    Join Date
    Feb 2008
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    Western NC
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    2,504
    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.
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,081
    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.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,171
    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.

  5. #5
    Join Date
    Apr 2002
    Location
    Omaha, NE
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    1,561
    Quote Originally Posted by iraqveteran View Post
    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.

  6. #6
    Join Date
    Jul 2008
    Posts
    33

    Need more info

    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.

  7. #7
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
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    3,718
    Quote Originally Posted by Anthony49 View Post
    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.

  8. #8
    Join Date
    Jan 2005
    Posts
    113
    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

  9. #9
    Join Date
    Jul 2008
    Posts
    20

    here i am

    Quote Originally Posted by thegoodlistener View Post
    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

  10. #10
    Join Date
    Jul 2007
    Location
    Memphis,Tn
    Posts
    8

    20 Degree split

    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.

  11. #11
    Join Date
    Jul 2008
    Location
    Denver, CO
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    4,229
    Quote Originally Posted by cnpro18 View Post
    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

  12. #12
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,677
    Quote Originally Posted by Anthony49 View Post
    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)
    You can't fix stupid

  13. #13
    Join Date
    Jul 2005
    Posts
    11
    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.

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