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  1. #14
    Join Date
    Aug 2016
    Location
    Houston TX
    Posts
    33
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    Nitrogen does not absorb moisture. This is why you must do a triple evacuation. As you are pulling a vaccum the moisture will boil off. The vaccum does not suck the moisture out. As you are running the vacuum that moisture will freeze. The breaking the vacuum with nitrogen will allow the moisture to absorb heat helping it move in the system and increasing water vapor pressure. Due to you not being able to pull a vaccum down to microns then that tells me you have leak/leaks. If your gauge is working correctly. Also, on a system that large I would recommend getting a larger then a 5cfm pump and using a larger 3/8 or 1/2 hose made for evacuation. I have pulled a 250 micron vacuum on systems of this size and larger in less then 3 hours and hold vacuum for 24hrs. If you pull a vaccum down to 500microns and it starts to rise but then stops that shows you have moisture in the line. If you brazed with a nitro purge from the outdoor unit make sure you have the pressure high enough to reach the area you are brazing. If you have 2psi at the outdoor unit then 50ft from there, there will not be enough nitrogen to prevent oxidation. The micron gauge should be placed on the system and not the core removal tool as well. Preferably on the liquid line if it is a heat pump and hp/lp gas line on heat recovery.

  2. #15
    Join Date
    Oct 2014
    Location
    Columbus, Ohio
    Posts
    1,349
    Post Likes
    Quote Originally Posted by Lddc View Post
    The vaccum does not suck the moisture out. As you are running the vacuum that moisture will freeze.
    Just as a point of note, I would recommend searching for vacuum videos on YouTube by Jim Bergmann. He has shown that it's unlikely that you will ever get moisture to freeze in the real world when vacuuming a system. Under a deep enough vacuum, moisture will definitely boil out, but it can get trapped in the oil which is where the nitro sweep comes in.

  3. #16
    Join Date
    Apr 2017
    Posts
    8
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    Thread Starter
    Update
    OK so based on the advice given and what's recommended in the manual I re-pressurized the system again. Our company regulator will only go up to 400 psi on the outlet side, so I tested at that (I do realize it is supposed to be 600 but I'm forced to work with what's available). I was able to find a leak on one of the flares. Rather than tighten, I opted to just re-flare, deburr, clean and put more nylog on (which I was forced to buy with my own money if you can believe that, what a s@#t show!!). Unfortunately by boss only allowed me to do a standing pressure test for an hr and not the recommended 24 like specified in the manual. There was no drop. I went out and bought bubbles for refrigeration and sprayed everything down just to be safe and found no other leaks (you'd think we'd have some for installs, but no, yet another expense on my end). Finally once I felt we were leak free, I purged my nitrogen and began to pull my vacuum. Pulled down to 500 microns and saw it rise to 785 microns within 20 mins. Below you'll find the evacuation procedure outlined by Mitsubishi. Basically they seem to say that if vacuum hasn't increased 130 Pa in an hr (which was 975 microns when i converted) you are good to go. I wasn't allowed the proper time, but after 20 mins I went up just short of 300 microns (went from 500 to 785). If I was allowed to do the full amount of time by my boss i suspect based off the rise I saw In 20 min I would've only rose to about 900 microns. Now I know procedure was disregarded and I tried my best to do it the correct way, but given what I've stated, do you guys think this system is going to be fine? Thanks in advance for all your help guys!!!!

    Use a vacuum pump with a check valve.
    --If the vacuum pump oil flows back into the refrigerant lines, the refrigerant oil may deteriorate and the compressor
    may malfunction.
    <Evacuation procedures>
    ① Evacuate the system from both service ports, using a vacuum pump with the service valves closed.
    ② After the vacuum reaches 650 Pa (0.0943 psi/5 Torr), continue evacuation for at least one hour.
    ③ Stop the vacuum pump and leave it for an hour.
    ④ Verify that the vacuum has not increased by more than 130 Pa (0.01886 psi/1 Torr).
    ⑤ If the vacuum has increased by more than 130 Pa, water infiltration is suspected. Pressurize the system with dry nitrogen gas up to 0.05 MPa
    (7.25 psi/375 Torr). Repeat ① though ⑤ until the vacuum is increased by 130 Pa or below. If the results persist, then perform the "Triple
    Evacuation" below.
    <Triple Evacuation>
    ① Evacuate the system to 533 Pa (0.07729 psi/4 Torr) from both service ports, using a vacuum pump.
    ② Pressurize the system with dry nitrogen gas up to 0 Pa (0 psi/0 Torr) from the discharge service port.
    ③ Evacuate the system to 200 Pa (0.029 psi/1.5 Torr) from the suction service port, using a vacuum pump.
    ④ Pressurize the system with dry nitrogen gas up to 0 Pa (0 psi/0 Torr) from the discharge service port.
    ⑤ Evacuate the system from both service ports, using a vacuum pump.
    ⑥ After the vacuum reaches 66.7 Pa (0.09672 psi/5 Torr), stop the vacuum pump and leave it for an hour. A vacuum of 66.7 Pa must be
    maintained for at least one hour.
    ⑦ Verify that the vacuum has not increased for at least 30 minutes.

  4. #17
    Join Date
    Jun 2014
    Location
    Dover, DE
    Posts
    9,431
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    The startup guy may say your install is no good and refuse to commission the equipment.
    I dont understand why your boss is not allowing for a proper startup, and is installing a very sophisticated unit with inadequate tools and supplies.
    If I was your startup tech, Id have told him tough luck and left.
    Once you get your post count up Id suggest becoming a professional member here. Its free and theres a wealth of educational material behind scenes.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

  5. #18
    Join Date
    Apr 2005
    Location
    Australia : Queensland
    Posts
    1,650
    Post Likes
    You need to pressure test to at least the design running pressure

    150psi is only 11.3'Celcius
    your head pressure could be at least 70-80'C which would give you over 600psi.
    The primary function of the design engineer is to make things difficult for the fabricator and impossible for the serviceman.

  6. #19
    Join Date
    Oct 2014
    Location
    Columbus, Ohio
    Posts
    1,349
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    Realistically it may work, and maybe even for a good long time. But I wish you best of luck with the startup tech.

  7. #20
    Join Date
    Apr 2017
    Posts
    8
    Post Likes
    Thread Starter
    Well, I tried anyway lol. The answer to your why? Government job. Don't want to disclose where, but it's the wild west when it comes to doing things to code and proper technique. It's beneficial in the sense that I'm given the opportunity to do things a rookie shouldn't be doing (sink or swim here), but the draw back is not being able to do things right. I'm a former finish carpenter of over a decade and recently started a plumbing apprenticeship/hvac apprenticeship (2 years ago) and it truly pains me the way we do things. It sucks because I'm making rate right now, and I have been for my entire apprenticeship, because otherwise I would've left a long time ago. It truly pains me to hack and slash the way I'm forced to. As we say in my area "It is what it is." Hopefully I can get my post count up and become a member because I really pride myself as a craftsman and it bums me out having to do things fast and incorrectly to "get r done." Hopefully it will last a year because after that, our company is off the hook.

  8. #21
    Join Date
    Apr 2018
    Location
    SW Ohio
    Posts
    59
    Post Likes
    What a mess. Good luck with that.

    Sent from my SM-G900V using Tapatalk

  9. #22
    Join Date
    Dec 2014
    Location
    New Mexico
    Posts
    804
    Post Likes
    Where in the Wild West you talking about ,we are needing a tradesman that can learn and grow. I will make you do it right!


    Sent from my iPhone using Tapatalk

  10. #23
    Join Date
    May 2004
    Location
    Salt Lake City/Tooele
    Posts
    4,901
    Post Likes
    Probably, Utah.

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