The Wall
  • Post a Reply to this Thread

    vacuum (21 Posts)

  • Paul S Paul S @ 6:16 PM
    Contact this user


    Can anyone explain to me what is the correct time to evacuate a system....or is it once the system is at a certain amount of microns?....
  • Techman Techman @ 9:28 PM
    Contact this user

    How long?

    1hr,10hr,100hr. The micron gauge will tell. I had a blast freezer( -25*F) for ducks. After a failed water cooled cond that flooded the entire system,after draining out as much water as possible,and after the better part of a week (24-7 ) after many vacuum pump's (3) oil changes (5-7 times a day) ,I was able to pull no lower than 5-6,000 microns. With pressure from management (and 40-50 jobs at stake ) the system was started . The suction filter/driers looked like a vanilla Carvelle after 5min or so, so, the F/D were changed many many times(5-6 cases of 12 ,replaceable cores) until the moisture/water was gone.But ,lots of people were back at work! Yea, it's the micron gauge. How many inches in a perfect vacuum? How many microns in an inch? How many negative lbs. of pressure is that? Absolute scale? PSIG scale?
    This post was edited by an admin on April 14, 2013 9:39 PM.
  • unclejohn unclejohn @ 10:50 PM
    Contact this user

    The correct time

    To evacuate a system is after all the holes are filled and there are no more leaks. Rim shot boom. Take my wife, please take my wife. Or as Tech says after all the mositure is gone or in his case the flood has subsided.
  • Spence Spence @ 8:57 AM
    Contact this user


    If you are working with R-410A, it is a real challenge to get the moisture out, so try not to leave the system open to atmosphere for more than 15 min. Always remove your valve cores to vacuum, and use a vacuum hose, not refrigerant hoses. Run your pump (with clean oil) to 200-300 microns and isolate the pump. If your micron gauge rises to 500 microns and stays, job well done. Continuing rise means moisture is still in the system, or you have a leak. With R-410A, it is near impossible to get all the moisture out, so if your microns rise to 750 for example, and you have done a triple evacuation, you have done the best you could under the circumstances. Again, minimize exposure to atmosphere and oversize your LLD as a matter of practice. On your annual maintenance calls, check the temperature drop across the drier. Anything more than 3 degrees, out it comes!
  • unclejohn unclejohn @ 12:07 PM
    Contact this user


    A valve core?
  • Spence Spence @ 12:13 PM
    Contact this user

    Valve Core

    Commonly called Shrader valves, they look like the valve in a tire. You cannot pull a quality vacuum with them in the service valve.
  • unclejohn unclejohn @ 10:31 PM
    Contact this user

    how do you

    get them back in after you pull a vacuum?
  • Spence Spence @ 10:55 AM
    Contact this user

    Replacing Valve Cores

    Good question; love it! Here are a couple of ways: (1) Install a core removal tool with side ports for vacuuming. When you are happy with your evacuation, push down on the plunger and screw them back in. (2) If you don't have the above tool, don't forget we are allowed de minimus release of refrigerant into the atmosphere, so introduce just enough refrigerant to break your vacuum. If you're quick enough, you can get the core in before all of the pressure is released so you don't disturb your vacuum or burn yourself. Then repeat the process for the other line. It may sound crazy, yet I have done this hundreds of times before the days of the above mentioned tool. The trick is getting the core in before the refrigerant empties.
  • unclejohn unclejohn @ 7:14 PM
    Contact this user

    Seems to me

    Your forgetting about vapor pressure, which means regardless of the refrigerant pressure in the pipe if the vapor pressure is lower in the pipe [which it should be if you just pulled a vacuum] then in the air surrounding the pipe you will introduce moisture back into the system. Basically the same way moisture gets into the supply side of a duct if you don't seal all the joints with tape or duct seal.
  • R Mannino R Mannino @ 9:04 AM
    Contact this user
  • Spence Spence @ 11:18 AM
    Contact this user

    Core Tool

    By sending this picture, the tech is showing us that he uses them. By using them, this seemingly tiny little issue speaks volumes about the quality and performance of his work in the field. I'll bet his air conditioner and heat pump installations last 20 years!
  • Techman Techman @ 11:08 AM
    Contact this user

    Schrader inserts

    Both Spence and R Mannino are correct.But I do admit to doing it the same way as Spence ,ala "de minius".But ,also, R Mannino's way is food for thought.
  • Spence Spence @ 8:03 PM
    Contact this user

    Core Tool

    I only mentioned the old way in case the tech does not yet have a set like the ones in the picture, which I now use as well. No more fried digits or valve cores down my shirt!
  • N/A @ 7:43 PM


    Use a micron gauge after you made sure the system has been flushed with dry-nitrogen and pressurized up to 500 psi. And the hits just keep coming in.

  • heatpro02920 heatpro02920 @ 9:34 PM
    Contact this user

    David that takes too long.

    Just blow some refrigerant through with one side open, close it and vawala no moisture, lol... Im just kidding, I had a tech that was applying for a job tell me that is the way to do it... He also said that he would never replace a txv just because a compressor stopped working, I said flushing the lines and changing a few cheap parts is good insurance, he said "nahhh, too much work", needless to say he never got hired, but I did see him working for someone else about 2 weeks later...
  • Paul Fredricks Paul Fredricks @ 2:07 PM
    Contact this user

    I remember

    Back in the day, the directions that came with Sanyo ductless splits said to leave the suction line port open and crack the liquid valve open for two seconds. The liquid would expand and vaporize, pushing the air out of the liquid and suction lines.
    I have never pulled the schrader cores, and never had a problem pulling a good vacuum. I can see it slowing things down a little for the first few minutes, after that the flow rate is so low that I can't see it making a difference. Of course, I'm talking residential sized units.
    And, it seems to me, that 410 shouldn't be that much of an issue. If the system is empty, just purge nitrogen through the system. There shouldn't be much, if any, 410 holding on to moisture. Sure, there will always be a little, but I can't see it making that much of a difference. I always pull down to at least 500 microns, 250 is better still.
    Just my 2 cents.
    This post was edited by an admin on April 23, 2013 2:09 PM.
  • Techman Techman @ 6:57 PM
    Contact this user

    Back in The Day!

    Paul, you're old enough to say that? LOL. I remember "back-in-the-day" I was taught to blow out dirty (refrig) condenser coils with good ole' R-12. I also remember Carrier and Virgina Chemical Co. and others teaching me how to "triple evacuate" a system by breaking each evacuation using R-22. And to "purge" the system initially using  R-22 . And one more "back-in-the-day" thing, we had only 3 freons (r12 r22 r502) AND THEY TOOK CARE OF 98.6% OF THE UNITS WE WOKED ON. Now I have 20 drums for  freons and recovery. Go figure!
    This post was edited by an admin on April 23, 2013 7:01 PM.
  • Paul Fredricks Paul Fredricks @ 9:06 AM
    Contact this user

    the day

    We did have one or two units that used R-500 (yellow can?), a blend of 12 and 22 that old carrier equipment used. We also used R-11 to flush systems after a bad burn out. Just pump it in one side and let it dump out the other onto the ground. No wonder the ozone is in such bad shape.
  • drhvac drhvac @ 4:01 PM
    Contact this user

    how to vacuum with core tool

    This is how you evacuate with a core tool. It works great!
  • Techman Techman @ 9:53 PM
    Contact this user


    Thats a pretty steep price for only two hoses.
  • drhvac drhvac @ 9:34 AM
    Contact this user


    I actually use 3/8 hoses which work fine. What I meant to post is if you go to youtube and punch in jim bergman evacuation, the guy shows you an evacuation using the valve core tools. They also have a hose set up they use off of the pump that makes things very easy to hook up and use. You don't have to buy the whole evacuation kit they sell, you can build your own kit which I did because I already had some of the stuff.
Post a Reply to this Thread