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  1. #1

    Test before calling for service question

    I came across this example of a correctly running cap/orifice system and wanted opinions on its acuracy before using it to evaluate our system to determine if we need to call for service. Just bought the building; 1900 sf and the 3 ton 10 SEER unit does not seem to be getting the job done:

    Air Conditioning

    This example is for a 10 SEER system. The unit is running normally, and the space is within about 5 degrees of the desired final temperature.
    Condensing pressure should be equivalent to somewhere around 20-30 degrees above ambient.
    Evaporator pressure should be equivalent to about 38-42 degrees.
    Look for 20-30 degrees of superheat at the compressor: less than 20 degrees is not acceptable.
    Look for 5-15 degrees of subcooling on the liquid line at the outlet of the condenser.
    Look for return air temperature to drop about 15-20 degrees as it passes through the evaporator coil.
    The temperature of the air entering the condenser should rise about 20-30 degrees as it passes through the condenser coil.

    Thanks

  2. #2
    Join Date
    Apr 2005
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    N. E. Missouri
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    A professional would not only know how to obtain all that information, they would know what to do with it (i.e. what it means).
    If you feel that your system is not maintaining a comfortable temperature for you and it is running, filters are clean etc. then you should by all means call in a professional. Even if you obtained all that information, what would you then do with it?

    Oh yeah, since you're a new member, maybe re-read the rules presented to you when you signed up.

    No DIY.
    Do not argue with an idiot. He will drag you down to his level and beat you with experience.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    With 1 or 2 exceptions. What you posted was inaccurate rule of thumb that tells you nothing.

    I wouldn't rely on that to tell you if the system needs service or not. You might end up thinking your system is fine. And continue to run it under that false impression and kill the compressor.
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  4. #4
    Join Date
    Jun 2007
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    Round Rock
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    I like the 20-30 degrees hotter than ambient pressure thing. I really hope not. Otherwise we'll be cooking. Call somebody to check it out. Don't be cheap. It's not cost that much to get an evaluation. You'll spend more than that on a nice night out with the wife.

  5. #5
    I specifically said this was in preparation of calling in a Pro, so why you have an attitude and bring up DIY I don't know. It is funny how you assume no one would know how to do the measurements and I wouldn't know what they mean. I insulted no ones intelligence and deserve the same respect. Unless you are afraid of an informed consumer, I don't see the problem in any pro here commenting on this excerpt from a HVAC Professional in a 2008 publication. Unless you make your living charging folks for doing nothing or when nothing is wrong, what is the harm in the customer knowing what you are looking for and doing? Any honest pro should be happy to know their customer is not an idiot so that when they recommend the correct service the customer will understand and not complain. I know I was during the 25+ years I did auto repairs, which by the way did include refrigeration training and certification, along with welding, fabrication, electrical, hydraulics, combustion, lubrication, heat transfer, and many, many other systems training and certifications which make up the modern automobile. My intention is not to get over on a local HVAC professional, but to be an informed consumer. Any honest contractor would not fear that.

  6. #6
    Join Date
    Dec 2002
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    Houston,Tx.
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    Quote Originally Posted by firemunky View Post
    I specifically said this was in preparation of calling in a Pro, so why you have an attitude and bring up DIY I don't know. It is funny how you assume no one would know how to do the measurements and I wouldn't know what they mean. I insulted no ones intelligence and deserve the same respect. Unless you are afraid of an informed consumer, I don't see the problem in any pro here commenting on this excerpt from a HVAC Professional in a 2008 publication. Unless you make your living charging folks for doing nothing or when nothing is wrong, what is the harm in the customer knowing what you are looking for and doing? Any honest pro should be happy to know their customer is not an idiot so that when they recommend the correct service the customer will understand and not complain. I know I was during the 25+ years I did auto repairs, which by the way did include refrigeration training and certification, along with welding, fabrication, electrical, hydraulics, combustion, lubrication, heat transfer, and many, many other systems training and certifications which make up the modern automobile. My intention is not to get over on a local HVAC professional, but to be an informed consumer. Any honest contractor would not fear that.
    So you would condone this same attitude if I were talking my car to an auto mechanic? I should go to an auto forum and try and get all the info I can, so when I take it to the mechanic I can stand over his shoulder and make sure he is not ripping me off.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

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  7. #7
    Join Date
    Apr 2005
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    I'm sure being a mechanic for that long you didn't appreciate the customer telling you in advance that only "THIS" or "THAT" is wrong with their car based upon some things they either read in a book or on the internet. You will know a true assessment of the overall mechanical system can't be done by someone knowing only half (or less) of the required information.

    You can measure things all day long. If you don't know what to do with the information you are not only wasting your time but that of the professional who will then do his own measurements.

    You state that you don't feel your system is getting the job done. Find yourself a professional to evaluate your system and determine if there is a problem. He will do all his own measurements (for reasons I think should be obvious to a mechanic) and make his own analysis based upon his observations/measurements/knowledge and training.

    No honest contractor fears an informed consumer--but you gotta allow them to do their job, not try to tell them what you think you may or may not have learned through the internet.
    Do not argue with an idiot. He will drag you down to his level and beat you with experience.

  8. #8
    Join Date
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    Lancaster PA
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    If you really knew what the readings mean. You wouldn't be asking the question, because you would already know the answer.

    An informed customer is a good thing.
    A customer telling me all the readings he took, and what he thinks it means slows me down. And cost him more.

    I also prep before I take my car in to be repaired. I tell them what it was or isn't doing. And have my check book ready.
    They have the tools and meters to find out what is wrong that its not working right. And I leave it to them to find it by their normal service procedures. Not by what I think they should check.

    Apparently, you don't trust what you read in that article, or you wouldn't have came hear and asked.

    That article is full of holes. And tells you nothing whorthwhile.
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  9. #9
    Join Date
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    Quote Originally Posted by Mr Bill View Post
    So you would condone this same attitude if I were talking my car to an auto mechanic? I should go to an auto forum and try and get all the info I can, so when I take it to the mechanic I can stand over his shoulder and make sure he is not ripping me off.
    Yeah, that's what I was gettin at, I just used more words and took more time to type!
    Do not argue with an idiot. He will drag you down to his level and beat you with experience.

  10. #10
    Join Date
    Aug 2003
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    Lincoln, Nebraska
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    As said most of the things you listed are useless information. Do you actually have a problem with your system? We can't give you step by step but may be able to give you ideas of what the tech may do or look for.

    DIY was mentioned just to make sure you read the rules and do not expect any specifics from us. I don't think is was meant to upset you. Your second post sounds even more like you want to check things yourself because you are so experienced in almost everything.

    I like informed customers but not ones that hang over my shoulder and try to tell me what to check or do. Make sure you find a reputable company and they should be able to explain to you what has happened and how to repair it.
    Its a good Life!

  11. #11
    I fully intend to call someone. I never owned this big of an open spaced building so unsure of what the performance should be like. It is an orifice system and am thinking on having a TXV put in. Any yeahs or nays?

  12. #12
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    Call a professional that can assess your needs.
    Simply put, we cannot assess your needs from here.
    Do not argue with an idiot. He will drag you down to his level and beat you with experience.

  13. #13
    Join Date
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    Converting to a TXV won't hurt the system. But it may not improve it any either.
    A TXV does NOT mean cheaper cooling bills.
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