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  1. #1
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    Mar 2013
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    txv troubleshooting

    Need some pointers on.the subject. Went to.a call.last week unit has high.superheat 30 and 9 degrees sub cool. Sst was 55 and head pressure was around 350 with a 90 degree ambient. R410a. I condemed the.txv because I took the.bulb off and held.it iny hand and.it didn't throttle any refrigerant at all.

  2. #2
    Join Date
    Jun 2011
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    398
    Did the bulb have good positive contact on the suction line? Was it insulated? Where on the suction line was it located? Is it an adjustable style txv? I've come across a couple txvs that have been fiddled with, adjusting the spring pressure brought SH back down and system was fine.

    Are both coils clean? Do you have sufficient air flow across the evap coil?

    Might be worth while to yank the charge and reweigh it in, could be a might low on gas, especially if people have had gauges on and off a lot. Is there a sight glass before the txv? If so, what is the gas doing?

  3. #3
    Join Date
    Feb 2007
    Location
    Central NJ
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    530
    Quote Originally Posted by timtanguay View Post
    Did the bulb have good positive contact on the suction line? Was it insulated? Where on the suction line was it located? Is it an adjustable style txv? I've come across a couple txvs that have been fiddled with, adjusting the spring pressure brought SH back down and system was fine.

    Are both coils clean? Do you have sufficient air flow across the evap coil?

    Might be worth while to yank the charge and reweigh it in, could be a might low on gas, especially if people have had gauges on and off a lot. Is there a sight glass before the txv? If so, what is the gas doing?
    Also, where is the drier, factory or field installed? What's the temperature and or pressure across it? Suction line drier?
    You have to pay your due's before you pay the rent!

  4. #4
    Join Date
    Dec 2005
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    1,921
    Quote Originally Posted by northeastbeast View Post
    Need some pointers on.the subject. Went to.a call.last week unit has high.superheat 30 and 9 degrees sub cool. Sst was 55 and head pressure was around 350 with a 90 degree ambient. R410a. I condemed the.txv because I took the.bulb off and held.it iny hand and.it didn't throttle any refrigerant at all.
    You diagnosed correctly.

  5. #5
    Join Date
    Jun 2014
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    38
    Quote Originally Posted by just_opinion View Post
    You diagnosed correctly.
    Basically.. I normally bring a glass of ice water as well... But if it ain't actuating.. case closed...

  6. #6
    Join Date
    Feb 2013
    Location
    Lamar, SC
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    612
    Quote Originally Posted by northeastbeast View Post
    Need some pointers on.the subject. Went to.a call.last week unit has high.superheat 30 and 9 degrees sub cool. Sst was 55 and head pressure was around 350 with a 90 degree ambient. R410a. I condemed the.txv because I took the.bulb off and held.it iny hand and.it didn't throttle any refrigerant at all.
    SST was 55, or suction pressure was 55? Was it really hot inside as well? 55 SST is pretty high, txv may have already been wide open in which case holding the bulb wouldn't make a change anyway. Need more info.
    Last edited by jmsmars1; 07-06-2014 at 04:41 AM. Reason: Need more info
    "If you've eliminated all other possibilities whatever remains must be the truth."

  7. #7
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    Quote Originally Posted by jmsmars1 View Post
    SST was 55, or suction pressure was 55? Was it really hot inside as well? 55 SST is pretty high, txv may have already been wide open in which case holding the bulb wouldn't make a change anyway. Need more info.
    SST was 55f which i also thought was high. superheat was 30 degrees so if valve was wide open then that wouldn't have been the case. and yes it was hot inside building.

  8. #8
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    Mar 2013
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    Maine
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    Quote Originally Posted by Bismarck View Post
    Basically.. I normally bring a glass of ice water as well... But if it ain't actuating.. case closed...
    thats a good idea i didn't think of that.

  9. #9
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    May 2014
    Location
    Ontario
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    118
    Agree with above about heat testing the blub and if the blub was wrapped. Those temps the valve should be open so you wont see any change. I would use something cold to test it. I have those flexible cold packs in my lunch cooler which work great when you can't get a glaass of ice water. Go back and forth from hand to pack and watch the gauges. Works everytime.

  10. #10
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    Feb 2013
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    Lamar, SC
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    Quote Originally Posted by northeastbeast View Post
    SST was 55f which i also thought was high. superheat was 30 degrees so if valve was wide open then that wouldn't have been the case. and yes it was hot inside building.
    Actually a txv can only open so much, so that very well could have been the case, especially if 1) the unit was slightly undercharged, or 2) the airflow is too high, or 3) the building is just too hot. Did you have access to a charging chart?
    "If you've eliminated all other possibilities whatever remains must be the truth."

  11. #11
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    Mar 2013
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    Maine
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    Quote Originally Posted by jmsmars1 View Post
    Actually a txv can only open so much, so that very well could have been the case, especially if 1) the unit was slightly undercharged, or 2) the airflow is too high, or 3) the building is just too hot. Did you have access to a charging chart?
    its a package unit so its weighed in charge. my first thought was it was a little low on gas but why would my SST be higher than what it should be? and compared to the other unit on the roof (identical model) it was almost identical pressures the only difference was my superheat readings. and compressor amp draw slightly lower

  12. #12
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    Feb 2013
    Location
    Lamar, SC
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    Quote Originally Posted by northeastbeast View Post
    its a package unit so its weighed in charge. my first thought was it was a little low on gas but why would my SST be higher than what it should be? and compared to the other unit on the roof (identical model) it was almost identical pressures the only difference was my superheat readings. and compressor amp draw slightly lower
    All I can tell you is if a txv fails to open your SST will be too low, not too high. If it fails to close your superheat will be too low, not too high. How can it be overfeeding (resulting in the high pressure) and underfeeding (resulting in the high superheat) at the same time?
    "If you've eliminated all other possibilities whatever remains must be the truth."

  13. #13
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    Mar 2013
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    Maine
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    Quote Originally Posted by jmsmars1 View Post
    All I can tell you is if a txv fails to open your SST will be too low, not too high. If it fails to close your superheat will be too low, not too high. How can it be overfeeding (resulting in the high pressure) and underfeeding (resulting in the high superheat) at the same time?
    I don't know. I was confused and thats why i posted this thread. maybe i messed up somewhere not sure...

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