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  1. #1
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    RTAA125 low on 22 or ...?

    got a call this morning RTAA125, circuit 2 "low refrigerant temp alarm", re-setted alarm. circuit-1 runs fine but circuit-2 runs for 20 seconds and trips on the same failure, suction pressure drops from 80psi to 20, liquid line stays at 108psi, there is no pressure drop across the dryers and the sight glass has some bubbles but it sort of clears right before the tripping point, all the operating settings are correct. my question is besides low refrigerant charge what else can cause the "low refrigerant temp alarm? I tested the EXV,the sensors and the water flow, all seems to be OK.

  2. #2
    Did you check the condenser fan? I'd start there.

  3. #3
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    How did you "test" the sensors? With the lack of rise of head pressure, I'd be thinking restriction after all sensors are checked with gauges and/or checking their resistance.

  4. #4
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    sounds like the sensor just after the exv is bad or acting up, just remember if you have to replace it do not splice wires and replace both are sold in pairs the sst and sesnsor on suction line that is why they

  5. #5
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    Quote Originally Posted by ryan1088 View Post
    How did you "test" the sensors? With the lack of rise of head pressure, I'd be thinking restriction after all sensors are checked with gauges and/or checking their resistance.
    The resistance checked OK, I also, locked compressor 2, switched the EXV control wiring from EXV-2 to EXV-1 and circuit 1 ran fine using the inputs and outputs of loop 2, that pretty much eliminates sensor issues.

  6. #6
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    Quote Originally Posted by Jd chiller View Post
    Did you check the condenser fan? I'd start there.
    thats a really wild guess, come again

  7. #7
    Check unload solenoid should be energized on comp start and should draw about 45% rla

  8. #8
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    Pull the charge and weigh it back in.
    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.

  9. #9
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    Quote Originally Posted by summerhelp View Post
    Check unload solenoid should be energized on comp start and should draw about 45% rla
    This is we're I'd start. Watch your display on start up watch the amps for that circuit if they go much higher than 45% then it's starting loaded. The RTAA is an older chiller a lot of times after so many hours those screw compressors need gone thru and rebuilt. Don't pull out gas and weigh in New you'll be wasting your time. Been there done that, have had same problem you describe more than once and this is what it ended up being.

  10. #10
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    Quote Originally Posted by GOVHVAC View Post
    This is we're I'd start. Watch your display on start up watch the amps for that circuit if they go much higher than 45% then it's starting loaded. The RTAA is an older chiller a lot of times after so many hours those screw compressors need gone thru and rebuilt. Don't pull out gas and weigh in New you'll be wasting your time. Been there done that, have had same problem you describe more than once and this is what it ended up being.
    Lets think about that for a minute, if the compressor was starting loaded, how would the suction and discharge pressures behave? in this particular case suction drops down to 20psi and head pressure stays at 108psi (r-22) how can a loaded start could made that happen?

  11. #11
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    Quote Originally Posted by valdelocc View Post
    Lets think about that for a minute, if the compressor was starting loaded, how would the suction and discharge pressures behave? in this particular case suction drops down to 20psi and head pressure stays at 108psi (r-22) how can a loaded start could made that happen?
    Call Trane tech support and ask them. I had it happen on two different chillers last summer alone. The exv is stepped down and it sucks the suction pressure down real quick and it doesn't run long enough for it to build up head pressure. Like I've said I had it happen twice to me and according to Trane it's a very common problem on these chillers. I went through everything on the first chiller this happened to only to call tech support and they told me what was going on and sent me some literature to troubleshoot it with. Apparently the seals start breaking down in the screw compressors after so many hours and they need rebuilt.

  12. #12
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    Quote Originally Posted by GOVHVAC View Post
    Call Trane tech support and ask them. I had it happen on two different chillers last summer alone. The exv is stepped down and it sucks the suction pressure down real quick and it doesn't run long enough for it to build up head pressure. Like I've said I had it happen twice to me and according to Trane it's a very common problem on these chillers. I went through everything on the first chiller this happened to only to call tech support and they told me what was going on and sent me some literature to troubleshoot it with. Apparently the seals start breaking down in the screw compressors after so many hours and they need rebuilt.
    You may have a valid point, I think you are talking a bout the lip seals leaking, right? I cant see how a leaky lip seal can cause the loop to trip on "low refrigerant temperature" alarm.
    I know you are trying to help and Im thankful for that.

  13. #13
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    Quote Originally Posted by ryan1088 View Post
    How did you "test" the sensors? With the lack of rise of head pressure, I'd be thinking restriction after all sensors are checked with gauges and/or checking their resistance.
    i think that this advice has been glossed over.


    Quote Originally Posted by valdelocc View Post
    The resistance checked OK, I also, locked compressor 2, switched the EXV control wiring from EXV-2 to EXV-1 and circuit 1 ran fine using the inputs and outputs of loop 2, that pretty much eliminates sensor issues.
    checking the resistance is a ridculous concept in most cases. the only thing that checking the resistance verifies, is if the board is converting the reistance properly...i have yet to find a system where the board converts improperly. i could happen if the board craps out, but that is rare in itself. check pressures with gages.
    When the rich wage war, it's the poor who die - Linken Park

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