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  1. #1
    Join Date
    Nov 2011
    Location
    South Texas
    Posts
    60

    RTAA code 190 low superheat (temp sensor out of cal)

    Early this year everyone here with gracious help pointed me in the direction until we found slide valves wore out. Rebuilt them and she has run like a top until this evening. I got a call around 6 circuit A is tripping on code 190 low superheat. I couldn't sleep so went out tonight to check it out while it's cool and quiet no one to bug me.

    On startup the unit runs for about 30-45 seconds not long enough to get any stable system readings then shuts down pops 190.
    All condenser fans are working cocrrectly and the coil has been pressure washed every quarter by me.
    -------------------------------------------------------------------------------------------------------------------------------------------
    All of the readings below were taken with the machine off and about 2-5 minutes after it tripped out

    I think the Evap refrigerant pressure sensor is where the majority of my trouble lies but please double check my logic. I used a brand new sman 2000 for all psi readings I took for this.

    Sensor 1 evap refrigerant temp sensor reeadings taken at the access port 3 inches in front of the sensor but behind the exv I read 98 psi on my gauge manifold and at the UCM I was reading 175psi for evap refrig press. my assumption sensor toast wo removing sensor to do full test as per trane TSB.

    Sensor 2 compressor suction temp. 98 psi actual reading on svc valve at compressor. Pt chart conversion shows 58 degree at 98 psi for r-22. The UCM was displaying 77 degrees suction temp. My thoughts this sensor is out of calibration as well.
    Did I use the correct train of thought for sensor 2 diagnostics.

    Sensor 3 condenser refrigerant temp sensor. 165 psi reading on my gauges the UCM showed 166 for condenser refrigerant pressure.
    Based off my findings this sensor is AOK.

    Sorry for the novel but after reading through this It's looking like evap refrigerant temp sensor and compressor suction temp sensor are out of range and the cause of my problems.

    Just wanted to bounce this off a few others and get feedback or suggestions. Again I apologize for the length of this.

  2. #2
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
    Posts
    2,064
    All pressures displayed on the panel are actually converted from the temperature sensors. There are no pressure transducers. With a machine shut down, you can expect to see the suction temp equal to ambient temp, and since the panel converts that to pressure, it will be misleading. You can expect evaporator liquid temp to equal chilled water temp (again, with machine shut down). Unless your chilled water temp was in the 90's I would look at that. Is this a process application? A common cause of this diagnostic is overfeeding of the evap.

  3. #3
    Join Date
    Jul 2007
    Location
    The Hot South
    Posts
    1,316
    Quote Originally Posted by Nuclrchiller View Post
    All pressures displayed on the panel are actually converted from the temperature sensors. There are no pressure transducers. With a machine shut down, you can expect to see the suction temp equal to ambient temp, and since the panel converts that to pressure, it will be misleading. You can expect evaporator liquid temp to equal chilled water temp (again, with machine shut down). Unless your chilled water temp was in the 90's I would look at that. Is this a process application? A common cause of this diagnostic is overfeeding of the evap.
    He is absolutely right. You can't use pressure/temperature conversions when the machine is down as the chiller uses temp sensors and converts to pressure. In addition, even if the chiller was running, the suct temp wouldnt be converted to pressure as it is not the saturated temp. With machine off and cooled down, the suction temp should reading ambient temp since the sensor is sitting in the suction line. Saturated temp should be close to chilled water temp with water flowing. More than likely your going to find one of your 2 sensors not reading right. First, make sure you have a good connection at the plug on the EXV module and no wire nuts on the sensor wires, then if still not reading right, replace sensors. They come in a pair that is a matched set so you always replace both.

  4. #4
    Join Date
    Nov 2011
    Location
    South Texas
    Posts
    60
    Called trane first thing this and ordered a set of sensors for it. Next weeks to do list is now a bit longer.
    Thanks for ideas as always i just didnt want to pull it apart to verify sensors per the tsb last night and not have new sensors on hand ready to go in. I also ordered the nuts and orings

  5. #5
    Join Date
    Nov 2011
    Location
    South Texas
    Posts
    60
    This is on a comfort cooling application. Circuit b running like a champ. Its oversized enough that i had the ems contractors use one circuit as purely backup. It then switchs circuits back and forth every other week to keep them exercised

  6. #6
    Join Date
    Feb 2008
    Location
    Dubai
    Posts
    107
    Quote Originally Posted by R123 View Post
    He is absolutely right. You can't use pressure/temperature conversions when the machine is down as the chiller uses temp sensors and converts to pressure. In addition, even if the chiller was running, the suct temp wouldnt be converted to pressure as it is not the saturated temp. With machine off and cooled down, the suction temp should reading ambient temp since the sensor is sitting in the suction line. Saturated temp should be close to chilled water temp with water flowing. More than likely your going to find one of your 2 sensors not reading right. First, make sure you have a good connection at the plug on the EXV module and no wire nuts on the sensor wires, then if still not reading right, replace sensors. They come in a pair that is a matched set so you always replace both.
    “In addition, even if the chiller was running, the suct temp wouldn’t be converted to pressure as it is not the saturated temp.”
    Then how does display shows the suction pressure? When chiller is running the gauge reading and display reading of the suction pressure will be same.
    Whether it is superheated or saturation, pressure will be same. if I am wrong, please correct me.

  7. #7
    Join Date
    Jul 2007
    Location
    The Hot South
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    1,316
    Quote Originally Posted by moideen View Post
    “In addition, even if the chiller was running, the suct temp wouldn’t be converted to pressure as it is not the saturated temp.”
    Then how does display shows the suction pressure? When chiller is running the gauge reading and display reading of the suction pressure will be same.
    Whether it is superheated or saturation, pressure will be same. if I am wrong, please correct me.
    I guess I should have been more specific when I said 'suction temp'. There are 2 temp sensors on the low side: 'saturated suction temp sensor' which is located on the entering side of the chiller barrell just past the EXV, and 'compressor suction gas temperature sensor' which is located on the leaving side of the chiller barrell on the compressor suction line. In the above quote, I was referring to Nuclrchillers post where he was calling 'suction temp' the superheated gas entering the compressor, and 'saturation temp' the saturated evap refrigerant temp. The saturated suction temp sensor is the one converted to pressure and displayed on the screen. The suction gas temp sensor is not converted to pressure because it measures superheated gas and the pressure would never be accurate. The difference between the 2 temperatures is the suction superheat.

  8. #8
    Join Date
    Feb 2008
    Location
    Dubai
    Posts
    107
    Quote Originally Posted by R123 View Post
    I guess I should have been more specific when I said 'suction temp'. There are 2 temp sensors on the low side: 'saturated suction temp sensor' which is located on the entering side of the chiller barrell just past the EXV, and 'compressor suction gas temperature sensor' which is located on the leaving side of the chiller barrell on the compressor suction line. In the above quote, I was referring to Nuclrchillers post where he was calling 'suction temp' the superheated gas entering the compressor, and 'saturation temp' the saturated evap refrigerant temp. The saturated suction temp sensor is the one converted to pressure and displayed on the screen. The suction gas temp sensor is not converted to pressure because it measures superheated gas and the pressure would never be accurate. The difference between the 2 temperatures is the suction superheat.
    Thanks 123. I have read somewhere the condition of the refrigerant after immediate EXV is not proper the saturated condition. I have checked and connected a gauge after expansion valve of McQuay AGS chiller and found the pressure around 130 psig, same time the compressor suction port reading is 65 psig! how does it happen like this? carrier 30 series reciprocating chiller sensor for suction pressure reading located to the refrigerant inlet in the cooler head. Not fixed even the sufficient length and space after EXV

    mOIDEEN-dUBAI

  9. #9
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
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    2,064
    Thanks for cleaning up my mess, R123!

  10. #10
    Join Date
    Nov 2011
    Location
    South Texas
    Posts
    60
    Update. Replaced the sat evap temp sensor and the suction temp sensor and this solved my particular problem. Thanks for the help as always.

  11. #11
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
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    2,064
    Thanks for the update. Is this the same chiller talked about in the epic slide valve piston thread that you just updated?

  12. #12
    Join Date
    Nov 2011
    Location
    South Texas
    Posts
    60
    The same one. But i did slide valves back in jan and completely forgot to post an update until last night when i did the other 2 posts. I hate to leave those who helped out in la la land as to whether all the problems where solved or not thanks to their gracious guidance.

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