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  1. #1
    Join Date
    Jun 2018
    Location
    Portland, OR
    Posts
    38
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    Hunting TXV after replacement

    Today I had a unit that was short cycling. When I got there and started the unit it didn’t look to out of the ordinary, but then my high side pressure began to climb along with sub cool. It would bounce back down then up until it finally hit the high pressure switch. I couldn’t find any restrictions in the system, and began to test the TXV. Put the bulb in ice water, and unit immediately tripped on high pressure. Held the bulb in my hand, and unit ran normal. Thought this was a good enough sine to replace the TXV. Well when I replaced it the unit ran better, but still had hunting issues. Below are before and after readings.

    R-410A system
    Before new TXV
    Suction pressure 122
    SH 2-3
    Saturation temp 34

    Liquid pressure 400 climbed to 550
    Sub cool 30 climbed to 50

    Never ran long enough for delta T
    Compressor amps 16

    After new TXV
    Suction pressure 122
    SH 4-6
    Saturation temp 45

    Liquid pressure 300-400
    SC 15-30

    Delta T 20 degrees
    Compressor amps 12-14

    The customer didn’t want to pay for new refrigerant, so we pulled as much as we could into the condenser, and weighed out 3 lbs. I only added two pounds back into the system as we were afraid the unit may have been overcharged, and it’s easier to add refrigerant than to take it out.

    Any ideas on why my liquid pressure was fluctuating so much still along with the sub cool?

    T

  2. #2
    Join Date
    Feb 2012
    Posts
    419
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    It sounds like the first one was working if it was opening and closing based on temperature, unless I'm missing something. Where and how was the sensing bulb attached and was it insulated?

  3. Likes DavidDeBord liked this post
  4. #3
    Join Date
    Mar 2015
    Location
    Hamersville, Ohio
    Posts
    2,444
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    Brand/ Md.#/ Ser.# would greatly help, & is this a Heat Pump, or AC?
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  6. #4
    Join Date
    Jun 2018
    Location
    Portland, OR
    Posts
    38
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    Thread Starter
    Quote Originally Posted by Jigjoe View Post
    It sounds like the first one was working if it was opening and closing based on temperature, unless I'm missing something. Where and how was the sensing bulb attached and was it insulated?

    It was an American standard AC, and the evap coil comes with the TXV installed on the inside. They put the bulb down stream of the txv equalizing line. I thought that's how they where supposed to work but got told to replace it by supervisor.

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  8. #5
    Join Date
    Mar 2015
    Location
    Tx
    Posts
    834
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    30 degrees of sub cooling ? Why ?

  9. #6
    Join Date
    Jun 2018
    Location
    Portland, OR
    Posts
    38
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    Thread Starter
    Quote Originally Posted by oldguy1949 View Post
    30 degrees of sub cooling ? Why ?
    That is the question? Best I can tell from my research is that the old refrigerant I sucked back into the condenser was contaminated. I added 2lbs of virgin R-410A to the system as we had to reclaim 3lbs even after we pulled as much as we could into the condenser.

  10. #7
    Join Date
    Apr 2003
    Location
    St. Louis
    Posts
    376
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    If the txv settled down with bulb removed from line, move the bulb futher down the suction line if theres enuff bulb length. Valve might be hunting because liquid could be hitting it when it opens then closes.

  11. #8
    Join Date
    Jun 2018
    Location
    Portland, OR
    Posts
    38
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    Thread Starter
    Turns out I had air in the system getting trapped in the condenser. Looks like whoever installed the system never pulled a vacuum, and just dropped charge on the unit.

  12. #9
    Join Date
    Dec 2011
    Location
    Twin Cities Minnesota
    Posts
    507
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    If that doesn't work,check airflow.I corrected a pesty "hunting" issue on a new install by increasing 300cfm on a variable,flatten right out.

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