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  1. #79
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    Mar 2007
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    In the Conservatory with a Lead Pipe
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    BluVac tip
    I don't calibrate very often so I can't remember the procedure which is different between some BluVacs.
    Since it doesn't really take up space or weight you can write the instructions on a ziplock bag and keep it with where the gauge gets stored for when the next calibration time comes.

  2. #80
    Join Date
    Aug 2010
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    Coral Springs, Florida
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    Thread Starter
    Quote Originally Posted by itsiceman View Post
    I don't calibrate very often so I can't remember the procedure which is different between some BluVacs.
    The calibration procedure is slightly different for the µBluVac vs. the BluVac, LTE, and Pro(+) models.

    The µBluVac must be cooled to below -2°C prior to turning on in cal mode. The others are turned on in cal mode prior to being placed in the freezer.

    This was just a function of the number of buttons I had available to put the unit into calibration mode.

  3. #81
    Join Date
    Aug 2010
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    Coral Springs, Florida
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    Thread Starter
    The saga continues...

    Case 1: Liquid Water

    Liquid water can get into an AC system via a break in the line set, condenser, evaporator -- or anywhere within the refrigerant loop. Humid air drawn into the compressor will precipitate as water upon compression (compressed air cannot carry as much water vapor as air at ATM -- this is why your air compressor has a drain cock), or water can enter directly into a cut line set. Once the damage is repaired, determination that liquid water has been completely removed is important prior to recharging. Luckily, the nature of water is such that it is easily recognizable during evacuation.

    Water has a vapor pressure (also known as saturation pressure) that is dependent only upon temperature. At 100°C (212°F), the vapor pressure is approximately 14.7 PSI (760,000 microns). This accounts for why water boils at 100°C at sea level, and why the boiling point drops at increasing altitude. Conversely, the boiling point at a given pressure is known as saturation temperature and is read out directly as a feature of our Pro and Pro+ gauges.

    Here is a chart of water vapor pressure vs. temperature (1 Torr = 1,000 microns):


    Credit: Wikipedia

    At room temperature (i.e. 25°C /77°F), the vapor pressure of water is about 24,000 microns or about 1" Hg above absolute zero pressure (i.e. -28.9"). The maximum pressure reading on the BluVac gauges is 25,000 microns (the Pro series gauges have an "Evacuation Progress Indicator" that will begin registering pressure at around 120,000 microns). Therefore, it is easy to see that -- depending on ambient temperature -- a heavily compromised system may not even pull low enough to register anything but Hi-P on the display of the BluVac until all the liquid water is removed.

    During evacuation, if the gauge never reads other than Hi-P, and you are sure the gauge and pump is working (because you checked them first as detailed in previous posts), either a leak or water is likely the culprit. To determine if water is the problem, continue to pump and watch the pump oil through the sight glass. It will turn milky white if water is present. Keep changing the oil until you get a pressure reading on the BluVac.

    If the oil stays clear, a leak somewhere is most likely.

    Smaller quantities of water will simply cool as evacuation proceeds, causing the vapor pressure to drop to the current level of vacuum. The evacuation will stall (i.e. the pressure will stop dropping), usually somewhere between 1,000 and 5,000 microns). At this point, the water will "boil" slowly. You will be able to see this on the BluVac: the pressure reading (and leak rate) will become unstable (due to the pressure changes as vapor bubbles "pop"). Continued evacuation -- and frequent pump oil changes -- will eventually remove all the remaining liquid water, at which point, you should finally reach your evacuation target.

    Some have expressed concern of water freezing during evacuation. This is possible under certain conditions -- and will dramatically increase the time required to evacuation the water. The heat to boil water must come from somewhere, and if it doesn't come from the solid surfaces of the system it will come from the water itself. Generally, freezing will only occur if the ambient temperature is already close to freezing. One way to ensure freezing does not occur is to maintain the vacuum pressure above the point where the saturation temperature is greater than 0°C (32°F) while water is present. This pressure is about 4,600 microns.

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