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  1. #1
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    "Purging" non-condensables

    I recently read some old posts and wanted to open the floor for some more debate as there are valid arguments on both sides. Non- condensables suspected in system- can it really be pumped down- however there isn't enough condenser capacity to pump down the entire charge- split ac no receiver- cooled by running all the fans and separating with cold water and non- condensables "purged" from the coil header which is intact the discharge header. Would not the vapor and liquid coexist? So how do you know. Recovering the entire charge and blowing vapor off the tope not really feasable at this time- can handle few hours downtime but not that long if it can be avoided. So I subscribe to the therory that non condensables move throughout the system- not magically sit idle in the condenser. i think of the coil as a cylinder of gas- the vapor and liquid will co-exist in the condenser regardless of how cool I get it. I can't assume I can cool it and expect to see liquid purging out the header. I also do not believe that refrigerant can be "contaminated "by the presense of non-condensables, air moisture etc. POE oil absolutely but not the refrigerant itself. Ok bombs away
    Last edited by dave1234; 05-21-2016 at 12:08 PM.

  2. #2
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    We were discussing this in another topic.

    It is my opinion and experience that the fastest and most effective way to rid a system of non condensibles is to pull the charge, evac the system and recharge with liquid from the tank.

    Since air is non condensible, adding only liquid means you've eliminated the air.



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  4. #3
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    Quote Originally Posted by jpsmith1cm View Post
    We were discussing this in another topic.

    It is my opinion and experience that the fastest and most effective way to rid a system of non condensibles is to pull the charge, evac the system and recharge with liquid from the tank.

    Since air is non condensible, adding only liquid means you've eliminated the air.



    Sent from my SM-N920V using Tapatalk
    The trick to that is keeping the liquid from boiling and agitating the air&nons. You have to charge slowly and what we use to do is place the tank in a plastic milk carton crate with a garbage bag and ice, similar to how we would recover rooftop 1 on 1's in the middle of summer. Chill the tank, charge slowly and the air& nons stay at the top and aren't mixed back in.
    A pat on the back is nothing more then topical anesthesia for a knife.

  5. #4
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    If you are removing liquid, the liquid isn't going to boil much.

    Also, while I didn't mention it, it is good practice to stop charging before all liquid is removed from the cylinder to prevent any air entering the system.

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  7. #5
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    At that point after you recovered the refrigerant then vacuumed the system why would you put the contaminated refrigerant back in and run the risk of putting the non condensibles back in the system. Why not put new refrigerant that you know has no non condensibles


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  8. #6
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    Quote Originally Posted by Bhctech8 View Post
    At that point after you recovered the refrigerant then vacuumed the system why would you put the contaminated refrigerant back in and run the risk of putting the non condensibles back in the system. Why not put new refrigerant that you know has no non condensibles

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    I actually mentioned this in my op but I do not believe - and I'm open to valid discussion to the contrary- that you can contaminate the refrigerant itself with non- condensables. POE oil sure but not the refrigerant itself. Not to mention the cost of 200 lbs of 22. Hell with retrofitting to 407-C. I don't mind changing oil- I do mind the glide/fractionation potential especially since system is prone to leaks no matter how hard we try to stay on top of them

  9. #7
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    Quote Originally Posted by jpsmith1cm View Post
    If you are removing liquid, the liquid isn't going to boil much.

    Also, while I didn't mention it, it is good practice to stop charging before all liquid is removed from the cylinder to prevent any air entering the system.

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    Doesn't the liquid and air seperate in the cylinder and blowing the top (vapor port) of cylinder off until PT falls into place a good place to start

  10. #8
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    By doing that, you are boiling the liquid refrigerant, causing it to drop in temp.

    It will work, but simply removing liquid refrigerant from the tank works faster.

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  11. #9
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    True- but therorically wouldn't letting the temp rise back to ambient and fall repeating do it. I agree with the temp drop by purging vapor- I'm just educating myself here. So pumping down- cooling condenser and purging off header is just a myth?

  12. #10
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    You are right. Theoretically, purging from the highest point in the system can and will work.

    I've done it on larger systems where recovery is impossible.



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  13. #11
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    Yes put more often then not the condenser is not the highest point and in many remotes with no receiver there isn't enough pump down capacity to pump down entire charge into cool. I suppose one could install a tap in the true highest point of the system on liquid line and 100% liquid should expell- within epa guidelines of course

  14. #12
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    Which is another argument for doing it my way.




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  15. #13
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    Quote Originally Posted by dave1234 View Post
    Yes put more often then not the condenser is not the highest point and in many remotes with no receiver there isn't enough pump down capacity to pump down entire charge into cool. I suppose one could install a tap in the true highest point of the system on liquid line and 100% liquid should expell- within epa guidelines of course
    It doesn't matter where the highest point in the system is, when the compressor is running, it will collect the non-condensibles in the condenser and trap them there with a liquid seal until the off cycle.
    Theoretically, installing an access port on the highest point of the condenser would allow you to bleed off gas while running.

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