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  1. #1
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    Mar 2018
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    fluttering needle refresher course

    I need a refresher on what some different needle ftutterings on my gauges mean. I sometimes see a slow up and down of about 5 PSI and I don't worry about it, I figure it's the TXV figuring itself out or something. I have read on here about a slow up and down of 50+ PSI, but yesterday I saw a really fast flutter, so fast the needle was just a blur going up and down probably 70 PSI. What do these mean ? I remember reading they sometimes mean a restriction, sometimes an overcharge, and sometimes non condensables. What is the general rule of thumb ? Of course we'd verify our suspicion but what do you suspect first.
    I didn't have time yesterday to spend time on it, or to take SC and SH readings, but there are obviously serious problems with the unit, my liquid line was cooler than the suction line, cooler I believe than OAT so it must be boiling off in the condenser. There was no real difference in temperature across the filter drier. The condenser was very dirty so I cleaned it well, got a bit of a lower pressure but still the same crazy bouncing. I need to go back and check the SH SC. This is one of those bristle brush Trane units with the liquid and vapor headers with four branches off each. On all four branches the vapor line was close to 120 and on all four liquid lines the temps were about 62. I was hoping to find a big temperature difference somewhere to show a restriction, but I didn't see that.
    Hmmm, to be continued once I have my SH and SC.

  2. #2
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    Thread Starter
    Another thought is that a lot of guys around here just top off R22 with 422D, shouldn't cause fluttering, but no have no idea what that does to my P/T. Nothing good I'm sure.

  3. #3
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    Fast blur is probably vibrations or pulsations from the unit running, which is why they make liquid filled gauges and snubbers.

    Sent from my SM-N910W8 using Tapatalk

  4. #4
    Join Date
    Oct 2014
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    Quote Originally Posted by BALloyd View Post
    Fast blur is probably vibrations or pulsations from the unit running, which is why they make liquid filled gauges and snubbers.

    Sent from my SM-N910W8 using Tapatalk
    Second this. Accidentally put my low side hose on a discharge line that ended up running 450 psi...bent the needle. Get the right gauge on it and it was still fluttering.

  5. #5
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    Thread Starter
    Perhaps that is also going on, but there are definitely other chemicals mixed with the 22 that is causing it to have a different P/T. I was getting a 18 degree delta T across the evaporator, but my superheat for 22 was 28 and my subcool was 60. But physically there was actually a very small difference in temperature between the suction and liquid lines just past the valves.

  6. #6
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    You should probably post this in one of the pro forums. You'll get more information there, as we are limited as to what solutions we can provide in a public forum. That said, sounds like a restriction to me. Odd that your TS is OK. You should probably provide more complete information...particularly pressures, temps, type of equip, etc.

  7. #7
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    Mar 2018
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    Thread Starter
    Thanks. The owner is selling soon and my boss doesn't want me spending more time there so I guess I'll never know. I think that whatever is in there has a different P/T than R-22 and I recommended recovering and starting over if they want to know for sure that everything is operating properly.

  8. #8
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    Thread Starter
    Oh, and I thought I did post this in the pro forum, I'll need to pay closer attention next time.

  9. #9
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    May 2018
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    Sounds like a LOT of non-consumables, combined with overcharge.

    If it is a blend (assuming it’s clean) the most that could happen is a long temp glide). A blend when clean would not cause large spikes (flutter).

    ... an intermittent introduction of non condensed gas however would.


  10. #10
    Join Date
    Mar 2013
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    Quote Originally Posted by 3.14 View Post
    Sounds like a LOT of non-consumables
    Those non-consumables get you EVERY time!!

  11. Likes DavidDeBord liked this post
  12. #11
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    Jan 2013
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    Remove the whole charge into a clean suitable refrigerant recovery cylinder, weigh the charge at the same time and then do a standing pressure test and check charge weight is correct, if it doesn't match up, charge with new refrigerant, weighed in of course.

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