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    nobuck's Avatar
    nobuck Posts: 4, Reputation: 1
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    #1

    Apr 11, 2009, 01:16 PM
    Can I check for leaks just using vacuum pump?
    Hi My house is in the mountains and it is hard to find ac mechanic. My question is I vacuum my unit and it went down to 25 on my gauges I turn the pump off. It held at 25 for hours than it drop to 22 does this mean I have a leak. I do not have nitrogen. Should I get some to test.Do I have to buy a big tank and a regulator? Please help.

    Steve
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #2

    Apr 11, 2009, 03:58 PM

    You do mean -25. You could have a very small leak or it could be due to temperature changes or water outgassing from the system.

    You can try heating components and lines with a heat gun to see if the pressure increases.

    Prressurizing with nitrogen might help you find large leaks, but will not help with small ones. Pressurizing allows you to indentify if the system has a leak faster.

    Adding Freon and using an electronic leak detector will help with that.

    The old way was to attempt to draw the leak into a propane flame and look for a change in color of the flame.
    nobuck's Avatar
    nobuck Posts: 4, Reputation: 1
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    #3

    Apr 11, 2009, 05:50 PM
    Quote Originally Posted by KeepItSimpleStupid View Post
    You do mean -25. You could have a very small leak or it could be due to temperature changes or water outgassing from the system.

    You can try heating components and lines with a heat gun to see if the pressure increases.

    Prressurizing with nitrogen might help you find large leaks, but will not help with small ones. Pressurizing allows you to indentify if the system has a leak faster.

    Adding Freon and using an electronic leak detector will help with that.

    The old way was to attempt to draw the leak into a propane flame and look for a change in color of the flame.
    Thank you for your time and answer. Yes -25 It is new unit. Would you go with it then open up the valves
    letmetellu's Avatar
    letmetellu Posts: 3,151, Reputation: 317
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    #4

    Apr 11, 2009, 06:45 PM

    If you pumped it down to -25 and it is now -22 that means that you are sucking air into your lines, and the longer you leave the vacuum on the unit the more air and moisture you will have in the lines.
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #5

    Apr 11, 2009, 07:12 PM

    Make sure you check you gauge set for leaks too.
    dac122's Avatar
    dac122 Posts: 463, Reputation: 17
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    #6

    Apr 13, 2009, 08:22 AM

    On the really tough leaks, it is best to leave whatever charge you have in the system, charge with nitrogen to 200-300 psi and then sniff around with a leak detector. It took me several hours to find one on my mom's system, and the leak was so small, and hidden behind a bracket in the outdoor unit, the only way I could see it was to lay the detector below the leak and wait for the concentration to build and its heavier than air properties float down to the detector.

    If we're talking R-22, it is legal to charge with a small amount, add nitrogen and sniff around.
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