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    1300 microns! (12 Posts)

  • Timco Timco @ 8:27 PM
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    1300 microns!

    I can't seem to draw a system down below 1300 microns. Swapped a condenser on a 3 ton system and can't get a good vacuum. Can't find any leaks either. How long should it take a 5 cfm pump to bring a system with 75' of lines down to 250 microns?
    Working on steam and hot-water systems isn't rocket's actually much harder.
  • Ironman Ironman @ 9:14 PM
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    Leaking Somewhere?

    Have you tried to see if it will hold pressure or vacuum? If it does, then you either have a lot of moisture or your vacuum pump is worn. Are you sure your micron gauge is reading correctly?
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • Techman Techman @ 9:33 PM
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    How many systems have you used the same vac pump oil on ?What color are the evac hoses? How old are the gaskets in the hoses? What size is the hose attached to the vac pump? How long does it take?As long as it takes! There is no answer to that question.
    This post was edited by an admin on July 6, 2011 9:36 PM.
  • Timco Timco @ 9:38 PM
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    More cfm

    with a second pump I am down to 350 and falling slow. Yellow hoses larger size to pump. Must just be lots of moisture.
    Working on steam and hot-water systems isn't rocket's actually much harder.
  • Techman Techman @ 10:18 PM
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    Those yellow hoses are not for pulling deep vacuum's. But if you are at 350 microns,something is working.
  • N/A @ 3:27 PM


    well at least you have a micron gauge. Did you pressurize the system with dri nitrogen and run the pressure up to 425 psi and let it sit for 10 minutes. if you didn't why not. Did you use dri nitrogen when welding in the new unit, If not why?
    If you fine folks would just follow some very simple standards you would eliminate 95% of your problems even the professor would agree with me.
    1 - did you clean the indoor coil. 2- use nitrogen when you weld 3 - sweep with dri nitrogen and then pressurize with dri nitrogen 4 - evacuate down to at least 500 microns, i prefer my men to get 450 . 5 - put a new drier in the system.
    real simple follow these few steps and life will be so much easier on you
  • Timco Timco @ 3:46 PM
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    simple standards

    Thanks for your reply!

    Yes, I swept with compressed nitrogen while braising. I did in fact pressurize with nitrogen, but just to 100 psi to check for leaks. I did not read in any text book about getting up to 425 and I appreciate the advise.  As per Goodman's install manual, I pull down to 250 microns. Is this too far or a waste of time?

    When a different system I just did got down to 300 microns, it slowly rose back up to over 1000. I assumed leak, and re-pressurized. No leak. When I pulled down again, it got down to 300 and made an odd noise, and then the microns jumped to 800 with vapor at the pump outlet, then it settled back down. Water boiling out?

    At every AC service call, I examine the indoor coil and outdoor coil every time. I pulled a sheet of dog hair off of a indoor coil on a under-performing system last week.

    Last week, I had a system that would not pull down normal at all. I went
    to lunch (30 min) with the vac pumps running. When I got back, I was
    still at 800 microns. When I killed the pumps, the pressure DROPPED to
    400 microns and held fine. What happened there? Gauge issue?

    Thanks for the discussion. This is my first season offering AC and I am confident I can do this reliably. So far, great results.
    Working on steam and hot-water systems isn't rocket's actually much harder.
  • N/A @ 8:56 PM


    Most important thing of all make sure you use 90% rubbing alchol to clean your icron gauge out before each use or you will get in accurate readings LOL
  • Timco Timco @ 9:05 PM
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    Great advise! Thanks for sharing!! Going to clean them both tomorrow!!

    Working on steam and hot-water systems isn't rocket's actually much harder.
  • Techman Techman @ 9:07 PM
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    Get a set of hoses made for pulling deep vacuum's.! Are you using a 4-port manifold?
    This post was edited by an admin on July 10, 2011 9:11 PM.
  • Timco Timco @ 10:36 PM
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    My manifold (I call him Barry) is indeed a 4-port. Are you referring to the black hoses that are double the size and cost? A set of those and a nice vac pump tree will be next!

    No offense at all taken on the suggestions for the nitro! I need and appreciate all the advise I can get since I did not apprentice for this and have learned from text books. Can't wait to clean those gauges. My pumps are 5cfs and are good for 40 microns.

    Is 250 too low to pull each job down to?
    Working on steam and hot-water systems isn't rocket's actually much harder.
  • N/A @ 9:12 PM

    i learned the hard way

    after cleaning just hook your gauge to the pump and see what it pulls down to. I hope you didn't think i was being ugly about the dri nitrogen psi testing but it has served me well for over 35 years. no need for you to make the same mistakes i made
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