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  1. #105
    Join Date
    Feb 2010
    Location
    Nebraska
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    2
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    Hello gentlemen,
    I am a professional and have worked on everything from an itty bitty ice maker to a 500 ton centrifigul chiller. Here is my humble opinion on the subject. There is no definite answer to the question with so many varying circumstances. I had a 50 ton system one time with 150 foot of line set. We put 2-5 cfm pumps on it in the morning and went to a different area to work. It looked like everything was going good until lunch. This was a spring project and the system was coming down slow. The outdoor air temp was about 65 degrees faren. and dropped to 58 degrees by noon. We checked again and the micron gauge said 400 microns. Through experience I didn't believe what I was seeing , it came down to fast. I noticed a 20' sect of copper looked like it was sweating on the bottom not to far from the cond. I grabbed a torch and heated the pipe and lost the micron reading it went off the chart. Due to the weather change and the speed of the evacuation process we actually froze moisture in the system which fooled the micron gauge reading.
    So sometimes micron readings don't mean much and sometimes they do. Sometimes speed of change and common sense and a watchful eye can mean the difference between fixed and uh oh. So again there is no one formula, one time interval, one micron level or one situation. Unless you are in a lab with all variables controlled and unchanging and that just don't happen in the real world with the boss breathing down your neck.
    Then there is the { I'm losing money on this , just fill er up and get the heck outa there! }

  2. #106
    Join Date
    Dec 2008
    Location
    North Carolina
    Posts
    2,965
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    Quote Originally Posted by geno54 View Post
    When I first started I was taught to open the liquid line and purge three times for one minute each. No need for a vacuum pump. Shortly thereafter I got educated and learned the proper methods and why.

    For those of you who are members of RSES there was a Q & A (MSAC) in the Jan 2010 edition of the Journal regarding just this by Jamey Hale, CM, Technical Support Supervisor, ICOR International.
    http://www.rses.org/assets/journal/0110_MSAC.pdf
    Geno...definately worth the read, they have one at least once a year..For a very good reason. Still feel strongly not enough attention paid to maintenance of tools used though. Digital Gauges are nice, but you know what, have found a few sets guys used in the field that not maintained gave some very false readings. Technology has indeed improved things and made things quicker, but do not ever let go of the philosophy behind the principle otherwise the tools will make you look like an idiot.

  3. #107
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347
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    Quote Originally Posted by boscohvac View Post
    Due to the weather change and the speed of the evacuation process we actually froze moisture in the system which fooled the micron gauge reading.
    you knew something was wrong!

    these are scenario's that are almost impossible to teach



    .

  4. #108
    Join Date
    May 2007
    Location
    Dry as a bone Tucson
    Posts
    4,850
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    The wisdom of experience

    Quote Originally Posted by boscohvac View Post
    Hello gentlemen,
    I am a professional and have worked on everything from an itty bitty ice maker to a 500 ton centrifigul chiller. Here is my humble opinion on the subject. There is no definite answer to the question with so many varying circumstances. I had a 50 ton system one time with 150 foot of line set. We put 2-5 cfm pumps on it in the morning and went to a different area to work. It looked like everything was going good until lunch. This was a spring project and the system was coming down slow. The outdoor air temp was about 65 degrees faren. and dropped to 58 degrees by noon. We checked again and the micron gauge said 400 microns. Through experience I didn't believe what I was seeing , it came down to fast. I noticed a 20' sect of copper looked like it was sweating on the bottom not to far from the cond. I grabbed a torch and heated the pipe and lost the micron reading it went off the chart. Due to the weather change and the speed of the evacuation process we actually froze moisture in the system which fooled the micron gauge reading.
    So sometimes micron readings don't mean much and sometimes they do. Sometimes speed of change and common sense and a watchful eye can mean the difference between fixed and uh oh. So again there is no one formula, one time interval, one micron level or one situation. Unless you are in a lab with all variables controlled and unchanging and that just don't happen in the real world with the boss breathing down your neck.
    Then there is the { I'm losing money on this , just fill er up and get the heck outa there! }
    boscohvac, thanks for this great post! I am looking forward to reading more of your posts in the future.
    "Christ is the Son of God Who died for the redemption of sinners and was resurrected after three days. This is the greatest truth in the universe. I die because of my belief in Christ."
    Watchman Nee



  5. #109
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347
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    Quote Originally Posted by boscohvac View Post
    You are in a lab with all variables controlled and unchanging and that just don't happen in the real world
    too--shaay



    .

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