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Thread: Vacuum/Charging

  1. #1
    Join Date
    Jul 2006
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    35

    Vacuum/Charging

    Hi. I'm doing my AC ticket(2nd year) and need a little advice. I have the pump pulling a vacuum overnight on the unit. The micron gauge had pulled down to about 1000 microns before i left it for the night...so there doesn't appear to be any leaks in the system. When i go to charge the unit tomorrow...providing that the vacuum holds good(~500 microns)....my question is what to turn on and/or not to...when charging. Should i charge a bit into the low side first before turning the unit on? ....or should i turn the unit(compressor) on first, then open the low side on the manifold? Is it safe to run a compressor in vacuum before you start to charge? Thanks!

  2. #2
    Join Date
    Mar 2008
    Location
    SW Virginia
    Posts
    15
    weigh in the proper charge before starting,dont forget to calculate for line length.

  3. #3
    Join Date
    Oct 2007
    Location
    Southern Indiana
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    94
    Powering up a compressor under a deep vacuum will usually smoke the windings.

  4. #4
    Join Date
    Jul 2006
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    35
    Thanks guys. Disaster averted.

    So, as i charge vapour into the low side(without the unit running) where will the charge migrate to...the evaporator? ...some into the low side of the compressor? I was a little worried about the gas condensing somehow without the compressor running...

  5. #5
    Join Date
    Jan 2011
    Location
    Boston, MA
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    459
    Never run a compressor in a vacuum!

    Isn't there anyone at work that can help you?

  6. #6
    Join Date
    Oct 2001
    Posts
    6,956
    should of went for the liquid line with a purged hose and flip the can then go have coffee...get back the unit is ready to run.start it up and tweek the charge...never charge by gas cause once the system equalizes you'll have to jump the LP to get that liquid line to seal up at both ends
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  7. #7
    Join Date
    Jul 2006
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    35
    Quote Originally Posted by FrostyBeer View Post
    Never run a compressor in a vacuum!

    Isn't there anyone at work that can help you?
    Yes, there is....i just thought i'd ask here as well...for good measure and not to look like a retard.

  8. #8
    Join Date
    Apr 2012
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    Paper Street Soap Company
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    Weigh liquid into the "high side" liquid line and watch your low dide to see if it climbs.

    If its a split there should be a nomin charge on the side of the unit.

    Remember to purge your guages.

  9. #9
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172
    When charging a system after pulling a vacuum, I usually charge with liquid to both the high and low gauge ports on a system, most of the time on residential systems depending on the ambient temp, I can get pretty much the full charge in before running the system. After I have weighed in the charge I let the system set for a few min. while I take care of my vacuum pump and cords, then start the system and after it has ran for a few min check superheat and subcooling and add any remaining refrigerant needed to correct the superheat or subcooling. If it is cold out or a large system sometimes I will use my recovery unit to pump the entire charge into a system but you have to be sure all of the air is purged from the recovery unit and hoses before adding the charge.

  10. #10
    Join Date
    Jul 2011
    Location
    East coast USA
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    961
    Quote Originally Posted by desol View Post
    Yes, there is....i just thought i'd ask here as well...for good measure and not to look like a retard.
    Listen, ask your questions regardless what others may think. I rather look "mechanically challenged" than fry a compressor and be mechanically challenged!

    You say this is your second year in the feild, is this the first time charging a unit?

  11. #11
    Join Date
    Jul 2006
    Posts
    35
    In order for me to be comfortable with understanding a concept, i need to know the deeper sides the story. ...so, there is only de facto "liquid"(that kind that can damage the unit) in the last half of the condensor when the fans are running. True? When the unit is off(in vacuum)..liquid that is put in resorts to a gas state? How do i know that if i charge with liquid(from vacuum)...say like, todd says...on both sides...i won't slug the unit when i kick it on...?(weighed in...etc)

    Dlove: yes, it is. I've assisted before...but this is the first time on my own...plus i was away from work for a few months in school...etc.

  12. #12
    Join Date
    Nov 2006
    Location
    Southeastern Pa
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    18,260
    Quote Originally Posted by desol View Post
    Thanks guys. Disaster averted.

    So, as i charge vapour into the low side(without the unit running) where will the charge migrate to...the evaporator? ...some into the low side of the compressor? I was a little worried about the gas condensing somehow without the compressor running...

    I don't want to post the charging procedure in an open forum, and neither should anyone else.

    Get you count up to 15 and apply for pro membership, and you can ask again in pro residential.

    You will specific help there.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  13. #13
    Join Date
    Jan 2011
    Posts
    1,139
    The refrigerant type was never mentioned, but I was always taught NEVER to dump liquid into a machine under a deep vacuum.
    At 29" Hg R-22 is -130*F Can you imagine the temperature corellation for R-410a at 29" Hg when it's at -60*F at .9" Hg? The reason for not dumping liquid...thermal shock. Unusal stresses can be put on components when there are rapid temperature changes of that magnitude.

    If you became accustomed to that practice and did it in a chiller, the consequences suffered would be astronomical.

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