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  1. #1
    Join Date
    Nov 2003
    Location
    Ohio
    Posts
    114

    Removing air in a rack system

    I'm going to be working on removing air from a rack system on Thursday. Looking for the correct and best way to do this. My experience has been that shutting the rack down and running just the condenser fans for a time, then valve off the condenser and release the air off the highest point in the system. Thought's and advise please. Thanks
    It's a Leak!

  2. #2
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,080
    Back in the olden days...we used to install purge valves in an inverted loop at the condenser inlet. That practice seems to have disappeared from what I see from local market installations, so I hope you have a means of venting from the high point.

    For advice, I'm a bit rusty at this and others may have a much better approach but...

    First you need to get set up to measure condenser pressure and temperatures. I suggest attaching temperature probes at the inlet outlet and mid-coil to assure all are at the same temperature when you shut down. Energize the condenser fans, shut down the compressors and wait for the temps to settle out to ambient.

    Then with a T/P chart, determine what the saturated pressure should be for the temperatures you measured and compare that with what you get on the gauge. If you have significant non-condensible gases (NCG) you should see at least 10 psi difference or more.

    Now slowly vent from the top and monitor what the T/P relationship is doing. If you're venting NCG then the pressures should start to fall in line.

    Note that you may also have trapped NCG in the receiver, so that may have to be purged as well. It's handy if the system has enough isolation valving to accomplish this in a timely manner. Otherwise, it's just let 'er rip and hope for the best.

  3. #3
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,057
    Meister Pretty much nailed it.

    But you may need to come back and do it all again. sometimes the first time will not remove all NCG.

    Restart the system, let the gasses move around and come back to check it another day. And possibly purge again if needed.

  4. #4
    Join Date
    Oct 2003
    Location
    tidewater, va
    Posts
    2,081
    is it legal to do this?


    r404a

  5. #5
    Join Date
    Jul 2005
    Location
    Southern California
    Posts
    570
    not if your venting into a recovery cylinder
    Knowledge is knowing that a tomato is a fruit. Wisdom is knowing not to put it in a fruit salad.

  6. #6
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,057
    ain't nothin wrong with blowing air into air.

  7. #7
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,057
    Straight from the EPA.

    "Read Record Number 15 & 16:"

    http://www.epa.gov/ozone/title6/608/appdets.html

    they know you will be blowing off some refrigerant too...but just don't blow too much

  8. #8
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,057
    Heck read Record Number 2

    Says you can use refrigerant to pressurize to leak test, then blow it out.

    Because you are using the refrigerant as a leak testing gas and NOT as a refrigerant.

  9. #9
    Join Date
    Nov 2003
    Location
    Ohio
    Posts
    114
    Thanks for the replies. I'm a little rusty as well and wanted to make sure I had the process down. I knew I'd find some info here. I have done this process with the receiver and it worked. But it did take several trips back because you can only capture parts of the liquid charge at a time. I'll probably try both on tomorrows visit.
    It's a Leak!

  10. #10
    Join Date
    Jul 2005
    Location
    Southern California
    Posts
    570
    Quote Originally Posted by Phase Loss View Post
    Straight from the EPA.

    "Read Record Number 15 & 16:"

    http://www.epa.gov/ozone/title6/608/appdets.html

    they know you will be blowing off some refrigerant too...but just don't blow too much
    Well hey if they're OK with it....
    Knowledge is knowing that a tomato is a fruit. Wisdom is knowing not to put it in a fruit salad.

  11. #11
    Join Date
    Jan 2007
    Location
    Stongsville Oh
    Posts
    872
    Just for clarification. venting noncondensables from the highest point is not neccessary. Venting from the top of the condensor is. Non condensibles become trapped in the condensor. Hot gas is condensed then liquid flows throughthe expansion device flashing to a saturated vapor, the vapor then superheated is compressed. and non condensibles will not condense and remain in the condensor, it will not float to the highest point in the system. It will remain in the condensor unless the system is low on charge and ther is no liquid seal at the expansion device.
    ckartson
    I didn't write the book I just read it!

  12. #12
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,057
    nah, it will leave the condenser.

    Non-Condensable just means it will not condense (change state from a vapor to liquid)

    That's why you can see bubbles in the liquid line sight glass of a system with NCG.

    The high pressure side of the system is very turbulent in both high pressure and high velocity and will easily wick away NCG with it's flow and carry it throughout the system.

  13. #13
    Join Date
    Mar 2008
    Location
    kansas
    Posts
    127

    air

    I thought racks were supposed to have air in them that way you dont have to use so much freezonelol
    Honeywell you can buy better but you cant pay more

    I told my wife when i die to sell my fishing stuff for what its worth not what i told her i paid for it

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