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  1. #1
    Join Date
    Oct 2006
    Location
    tx
    Posts
    26

    txv low sh low sc

    replaced a compressor #1 on a goodman package unit. M#PCB120-3. Unit has txv. After starting and running for 20 min i was getting these readings. comp#1 rla 18.6, 13.1, 13.4 , 14.3. Blwr rla 8.4, 6.2, 6.0, 5.7. CF rla 3.5 , #1,3.0,#2,2.8. pressures 52/160. S.L. temp 31. sh 3. L.L. temp 87. sc 0. amb 70. ra 73. sa 54. return air grill is clean, as is evap, blowr wheel, and cond. Motor pulley has been changed and is maxed out. im thinking txv stuck open., but wouldnt i have a higher suction pressure. txv bulb is attached properly to line. ran out of time store closed will return to finish tommorow. what do you guys think.

  2. #2
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,847
    Quote Originally Posted by ats890 View Post
    replaced a compressor #1 on a goodman package unit. M#PCB120-3. Unit has txv. After starting and running for 20 min i was getting these readings. comp#1 rla 18.6, 13.1, 13.4 , 14.3. Blwr rla 8.4, 6.2, 6.0, 5.7. CF rla 3.5 , #1,3.0,#2,2.8. pressures 52/160. S.L. temp 31. sh 3. L.L. temp 87. sc 0. amb 70. ra 73. sa 54. return air grill is clean, as is evap, blowr wheel, and cond. Motor pulley has been changed and is maxed out. im thinking txv stuck open., but wouldnt i have a higher suction pressure. txv bulb is attached properly to line. ran out of time store closed will return to finish tommorow. what do you guys think.

    1) how did you charge the unit? Weigh in after a deep vacuum?

    2) where did you take the suction line temp?

    My first thought is that you have a heat transfer issue (low suction pressure, not enough heat getting into the refrigerant). In the case of a stuck open txv, it can be a case of more refrigerant than is needed for the available heat. After all, you do have 20 across the evap.

    A bad txv can be tested for by chilling and warming the bulb, and looking for changes in pressure. No change, bad txv. I'll trust that you DO know when a bulb is not correctly poitioned...

    It is possible that you found what killed the compressor, too.

    You did replace the dryer, right?

    You have enough posts for Pro. Get that done. I don't like to put this level of detail in the open forums.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  3. #3
    Join Date
    Mar 2011
    Location
    North Carolina Piedmont Area
    Posts
    448
    I would first verify that you have correct air flow by verifying total static pressure across the coil and confirm that it meets manufactures data specs.

    What is the outside ambient temperature when taking readings.
    What is return air temperature.
    Do you have some form of head pressure control.

    I would raise the head pressure to somewhere in the range of 200 PSIG before looking for problems. This can be accomplished many ways or as suggested by manufacture for low ambient control.




    But I am still learning and looking for a new mentor.
    _______________________
    In a strict sense troubleshooting is not part of the repair..........understand the symptoms and you will find a solution.

  4. #4
    Join Date
    Oct 2006
    Location
    tx
    Posts
    26
    I took suction temp at compressor . I did change drier . System failed acid test . I added suction drier and acid away. I pulled deep vacuum. My static pressure was 0.3 total. 0.17 supply. 0.14 return. Txv bulb placed at ten oclock. I will try warming bulb.

  5. #5
    Join Date
    Oct 2006
    Location
    tx
    Posts
    26
    I weighed in charge per nameplate. I will sign up for pro membrship.

  6. #6
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,847
    Quote Originally Posted by alcomech View Post
    I would first verify that you have correct air flow by verifying total static pressure across the coil and confirm that it meets manufactures data specs.

    What is the outside ambient temperature when taking readings.
    What is return air temperature.
    Do you have some form of head pressure control.

    I would raise the head pressure to somewhere in the range of 200 PSIG before looking for problems. This can be accomplished many ways or as suggested by manufacture for low ambient control.




    But I am still learning and looking for a new mentor.
    _______________________
    In a strict sense troubleshooting is not part of the repair..........understand the symptoms and you will find a solution.

    I have used a tarp and cardboard to artificially raise head pressure.

    We install low ambient when the cust is willing to pay for it. Not all will.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  7. #7
    Join Date
    Mar 2011
    Location
    North Carolina Piedmont Area
    Posts
    448
    Is that a twenty ton unit with 2-ten ton compressors?
    If thats the case it looks like you are not moving enough air. But you will need to cross reference with the data sheet.
    What size is the duct work for the return.
    What size is the supply duct.
    Is this a constant volume system.
    What is the space temperature which you are trying to maintain.

  8. #8
    Join Date
    Jan 2005
    Location
    Emerald Coast
    Posts
    933
    .

    OAT 70*.

    Bulb @ 10 o'clock, hmmm.


    ..
    Do not attempt vast projects with
    half vast experience and ideas.
    ...

  9. #9
    Join Date
    Feb 2013
    Location
    Soon I will be in NE
    Posts
    16
    I think the airflow guys are onto something

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