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  1. #1
    Join Date
    Jun 2005
    Location
    Colorado
    Posts
    34

    Question Using nitrogen while brazing and pulling a vacuum

    I understand the importance of using nitrogen when brazing to eliminate that black build-up of "soot" on the inside of the joints. I personally did an experiment brazing with and without nitrogen and then cut open the copper to see for myself. No "soot" with nitrogen!!
    I do have questions about blowing nitrogen thru the line-set after a repair to help remove moisture before pulling a vacuum. I've even read flushing nitrogen several times while pulling vacuum is the best way.
    After finishing a repair I always add 250 lbs of nitrogen and watch my gauges for about 10 minutes to make sure the pressure does not change. I assume this verifies the system has no leaks. When I vent the nitrogen is this considered “flushing” the system or do I need to blow nitrogen actually thru from one service valve to the other to do it correctly? To flow nitrogen thru the line-set to the evap coil I close off one of the sevice valves to force it thru but how do I force the nitrogen thru the condensing unit if that can even be done?
    I work on residential or small (up to 8-10 ton) commercial units.
    Also I hear allot about not using gauges to vacuum a system because they are "charging gauges" not "vacuum gauges". How critical is this?
    Any help on this would be great.

  2. #2
    Join Date
    May 2004
    Location
    Frederick, MD
    Posts
    879

    It's really

    useless to have gauges on a system while you are evacuating. It's more of a convenience so you can add (weigh in) refrigerant then start the unit. If you could have just hoses with isolation valves so you dont lose your evac., a micron gauge and vacuum pump, you should be good to go. Unfortunately some techs still believe in the "I pulled it down to 30" method".

  3. #3
    Join Date
    May 2010
    Posts
    1,291
    250PSI of nitrogen is rather high. I usually only put in 150psi - 200max. (if I can't find leak with 150).

    You're referring to nitrogen, vacuum, nitrogen, vacuum, nitrogen, vacuum, which is called doing a Triple-Evac. I don't always use this method unless I have burnouts or lots of moisture/contaminants in a system.

    Venting the nitrogen isn't "cleaning" out a system. Depending on the amount of acid/contaminents in a system I will disassemble all components (evap and condenser) of a system and shoot nitrogen directly through them with some R-22 to clean them out well, then braze back in. Some also use RX-11 flush.

    Using your gauges to pull a vacuum isn't recommended because it opens up the possibility of having more leak points in the system. Get Core Removal Tools, hook your Micron gauge to the side port of the core removal tool, remove the core, attach vacuum gauge directly to the rear of the core removal tool. Or you can get a vacuum tree and go this route. Use 3/8" hoses when possible. If using 1/4" hoses remove all the core depressors for a less restrictive vacuum. I recommend also getting a 1/4 tee so you can pull from both suction and discharge sides. Make sure you maintain your hoses and replace the seals every so often to prevent leakage.

    When brazing you want to use a flowmeter to get your nitrogen at 1PSI to prevent oxidization.

    If my memory serves me right, Copeland states that an appropriate vacuum is 750 microns

  4. #4
    Join Date
    Jun 2005
    Location
    Colorado
    Posts
    34
    Wow... thanks for the quick responses. Sometimes because of space a core removal tool can't be attached. What then? Also, how best to test gauges for leaks?

  5. #5
    Join Date
    Apr 2009
    Location
    San Diego
    Posts
    75
    i have been going on a lot of warranty calls this summer because of restrictions and have found the strainer on these new 410a systems clogged up from brazing without nitrogen. I get out to the jobsite and find the condenser cycling on high pressure. hook up gauges and have gotten up to 700 psig and 26 degrees of subcooling. evacuate system and find time and time again the same restriction. All of these calls could have been avoided by displacing the oxygen in the lines with nitrogen while brazing. I believe this is gonna become very common until the installers start reading the installation instructions or take some advice. This problem does not occur immediatly after the install and sometimes the installers have already been let go or moved on to another company. As for me, I learned by their mistakes and use nitrogen while brazing along with installing the filter dryer just upstream of the txv as the installation instructions recommend. I used to install the filter dryer outside at the condensing unit, but after seeing this service call time and time again, I changed my habits.

  6. #6
    Join Date
    Nov 2010
    Location
    N. Idaho
    Posts
    586
    Nitro flushing method helps push out any bad molecules still hanging on in the system.

    Havent done a ton of vaccums, but this past week I have been on a the hunt for a better method.

    Watch this series. Gonna be making a custom set-up soon for myself!

  7. #7
    Join Date
    Jun 2005
    Location
    Colorado
    Posts
    34
    Thanks again for the input. The youtube series is good... I too will be making a custom recovery/vacuum set-up. It'll be nice to always have everything together when I need it.

  8. #8
    Join Date
    Jun 2011
    Location
    Hammond,La.
    Posts
    1,176
    I wouldn't force high pressure through the condenser and release at high rates since it just blows out oil everywhere. In fact I don't like rapidly depressurizing any part of the equipment.

    For general leak testing I only put about 50 psi in if I just brazed the joints. If it is a system that has a leak that I didn't braze I will up the pressure. I never take my regulator off 250 even while flowing for brazing. I find it just as easy to barely crack the valve until you can just notice flow from your open port. I have a separate quality valve after the regulator near the end of my hose for this and so I can shut off the flow quicker if I need to without having the bottle right under my feet the whole time.

    Pressuring to 250 or whatever the systems test pressure is, is only for stability tests. If you have a weld that you are unsure of like on a king valve or compressor connection that was fubar'd and you had to try and fix it you might want to go to test pressures to make sure it will hold up.

    Not sure what you mean by flushing nitrogen while pulling a vacuum but you might want to check your pumps positive pressure limit. They are generally designed to start at 0 psi and with a maximum of 5 psi before you connect and start them.

    As for pulling a vacuum through the gauges, I use the SMAN3 which has a built in micron gauge and have found no problems using them. You just have to put a ball valve on the charging hose. With that said I am thinking of trying it the other way with a tree and separate gauge.
    "I am for doing good to the poor, but I differ in opinion of the means. I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it."
    Benjamin Franklin, 1766

  9. #9
    Join Date
    Nov 2010
    Location
    N. Idaho
    Posts
    586
    I should have made myself more clear.

    Rcb, you're right, I certainly dont go blasting 250lbs through the system to flush. I blank off my pump and vacuum gauge, undo low side and flush away

    And I dont ever go past 200 to leak check. I was taught 150 for 15min. One installer at my work goes like 350 on 410a systems. And another guy seems to think I need to leave it pressurized overnight So when I get there in the morning and obviously see a drop, when I already suspected a leak, I end up wasting my time, company time and customer time. I may be new, but I aint stupid!

  10. #10
    Join Date
    Jun 2011
    Location
    Hammond,La.
    Posts
    1,176
    Quote Originally Posted by Damien View Post
    I should have made myself more clear.

    Rcb, you're right, I certainly dont go blasting 250lbs through the system to flush. I blank off my pump and vacuum gauge, undo low side and flush away

    And I dont ever go past 200 to leak check. I was taught 150 for 15min. One installer at my work goes like 350 on 410a systems. And another guy seems to think I need to leave it pressurized overnight So when I get there in the morning and obviously see a drop, when I already suspected a leak, I end up wasting my time, company time and customer time. I may be new, but I aint stupid!
    LOL If I told someone that I was going to leave their system pressurized over night I might not get to come back or want to, the next day! Been hot as hell here

    One thing I have learned is that there are just about as many opinions of how to do something as there are techs.

    The very first guy that was trying to teach me how to do things ended up showing me so many bad habits that I never realized until I started being on my own and having to research everything for myself... now that was a wake up call
    "I am for doing good to the poor, but I differ in opinion of the means. I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it."
    Benjamin Franklin, 1766

  11. #11
    Join Date
    Nov 2010
    Location
    N. Idaho
    Posts
    586
    Most of what I have been learning during my first cooling season is trial and error, and lots of research.

    Talked to my other tech about keeping his micron gauge as far away as possible from the pump and not in line between the pump and his gauge, would be a better representation of what was happening in the system and not what the pump was doing to the gauge. He told me I was wrong and it didnt matter I told him he needed to do some research and learn. Needless to say that was not a good day between him and I

    Either way, I try to seek out facts and go from there

  12. #12
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,011
    I think this discussion belongs in pro residential.
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  13. #13
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,718
    Quote Originally Posted by Rcb2875 View Post
    I wouldn't force high pressure through the condenser and release at high rates since it just blows out oil everywhere.
    Haven't we all done this once......once....

    Not to steal Joe Piscopo's line in Johnny Dangerously...
    "The only true wisdom is in knowing you know nothing" Socrates

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