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Hot Rods Vintage Air Evacuation question

Discussion in 'The Hokey Ass Message Board' started by Rustytoolss, Aug 7, 2014.

  1. Rustytoolss
    Joined: Jul 27, 2009
    Posts: 252


    Getting ready to get my vintage air system operating. Got a question after I've pull vacuum on my system 45 mins @ 28.5", and closed the manifold knobs off.
    How long should my system be able to hold full/ or part vacuum on the gauges ??
  2. Forever.

    Think about it. If it won't hold vacuum, then it won't hold freon.
    Hill_County-rodshop likes this.
  3. brokenspoke
    Joined: Jul 26, 2005
    Posts: 2,921


    ^^^^^what he said^^^^^
    Joined: Jul 20, 2006
    Posts: 2,422


    Absoultely right if the system won't hold vacuum the system will also leak out all of your freon

  5. Grahamsc
    Joined: May 13, 2014
    Posts: 466

    from Colorado

    If there is any residual freon compressed into the oil it will " boil" out and simulate a leak
    If the system has been open or depresurized for a few days or longer all of the freon will have already " boiled " off .
  6. wsdad
    Joined: Dec 31, 2005
    Posts: 1,258


    Forever is a bit long to wait to see if it holds a vacuum. If it holds it for an hour, I'd charge it.

    However, if it looses ANY vacuum, even .5, find the leak. Double check that your hoses on your gauges are snug.

    " The way of fools seems right to them, but the wise listen. -Soloman
  7. wsdad
    Joined: Dec 31, 2005
    Posts: 1,258


    I meant to type, "half an hour" but I can't figure out how to edit it.

    " The way of fools seems right to them, but the wise listen. -Soloman
  8. jack_pine
    Joined: Jan 20, 2007
    Posts: 352

    from Motor City

    Remember, also that if there is any residual moisture held in oil or in desiccant material, it will continue to "boil" out after you shut the manifold off from vacuum supply. This will cause the system pressure to increase and "fool" you into thinking you have a leak. You really don't have any exposure to how much moisture is in the system or if it is really gone after a 45 minute evac.

    Anyway, I would use the 30-minute rule-of-thumb that wsdad suggested as a milestone. The longer you let it sit the more certain you can be of the system's integrity; leak-wise. An hour is as long as I would go
  9. bob35
    Joined: Aug 26, 2011
    Posts: 75

    from DFW, TX

    Maybe it doesn't need mentioning, but if you want to be sure you're system is leak free, make sure you run a positive pressure test (using nitrogen or moisture-free air). These systems don't operate in a vacuum, so finding or not finding a leak under vacuum really doesn't mean much. 200 psi is a good pressure for leak testing. I let mine sit for an hour or so, then depressurized, pulled vacuum for 30 minutes, then charged.
  10. D.Conrad
    Joined: Jan 8, 2010
    Posts: 453

    1. 1940 Ford

    Instead of relying on other guys opinions, call Vintage Air and they should be able to answer any of your questions.
  11. Joe H
    Joined: Feb 10, 2008
    Posts: 1,088

    Joe H

    On our school buses with 5 lb systems, we vacuum them for 1 hour then wait 30 minutes watching the gauges. If it holds vacuum for the 30 minute window, we hit it with 1/2 -3/4 lb of freon and wait 15 minutes for that to settle. On a hot day, the 1/2 -3/4 lb will be in the 50 -80 psi range depending on how hot the system. If I see the pressure hold, it takes just a few minutes to bring it back to a vacuum, then we add oil if needed and charge the whole amount. Its very hard to find a vacuum leak, but a pressure test is easy, and soap bubbles are easy to see.

  12. #1You did put a fresh dryer on prior to evacuating
    #2 ^^^^^^^ Joe H
    #3 if you suspect a leak, check your gauges first.
    #4 if you cannot find the leak, use Freon dye.
  13. I just re-charged my system after a new engine install. I was going to have a friend help me with the charge since I haven't done many. I had all the gauges and hoses hooked up several days before I was going to charge it up. I pulled a vacuum to be sure I didn't have any problems. After getting about 30 inches, I closed evetything off and waited. No leaks. So I said, why not leave it hooked up? What's the harm? The vacuum never decreased.
  14. Rustytoolss
    Joined: Jul 27, 2009
    Posts: 252


    This is a new system. It has held vacuum for several hours. But over night the vacuum is at zero.
  15. You must gave a leak, go back and check all your fittings and make sure they are tight.

    This stuff can drive you nuts, HRP
  16. greybeard360
    Joined: Feb 28, 2008
    Posts: 1,775


    You also have to remember that the system is designed to hold pressure, not vacuum. A brand new front seal can weep a little until it has run a short bit. If it holds for 30 minutes, should be good to go.

    Posted using the Full Custom H.A.M.B. App!
  17. Rustytoolss
    Joined: Jul 27, 2009
    Posts: 252


    I'm going to retighten all the connection again, then suck it down (sounds perverted) , watch the gauges, then shoot the 134a to it. Thanks to all.

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