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  1. #1
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    RTAA Chiller EXP Question

    We recently installed an RTAA-125 chiller with remote evaporator bundle inside an equipment room (40' away). Upon startup, we experienced EXP diagnostic failures even though service tests were fine. We were told to increase the wire size to the EXP's, but we'd probably experience intermittent failures. We were then told to relocate the outdoor EXP board inside (closer to the EXP's, less wire length) and add a "Buffer Board".
    Has anyone experienced this problem?
    Is there an easier way to resolve this?
    TIA,
    jogas

  2. #2
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    Quote Originally Posted by jogas View Post
    We recently installed an RTAA-125 chiller with remote evaporator bundle inside an equipment room (40' away). Upon startup, we experienced EXP diagnostic failures even though service tests were fine. We were told to increase the wire size to the EXP's, but we'd probably experience intermittent failures. We were then told to relocate the outdoor EXP board inside (closer to the EXP's, less wire length) and add a "Buffer Board".
    Has anyone experienced this problem?
    Is there an easier way to resolve this?
    TIA,
    jogas
    \


    You are talking about the EXV's correct?

    40ft is not that far, is that total wire length?

    If so, make sure the cables are at least 6 inches away from any higher voltaage wires.
    Make sure all connections are good, some times those insulation displacement connectors on the boards get loose. push the wire in good with a small flat blade screwdriver.

  3. #3
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    I service an 80 ton remote barrel RTAA that is more than 80 feet of wire length. I'd look at the connections at both ends, but most likely at the plug on to the valve. There's also a terminal strip in a j-box at the barrel.

    I used some non conductive GE silicone grease goop on a Carrier EXV one time that had sweaty multi-pin plug problems.
    God Bless the USA

  4. #4
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    After confirming the wiring was correct, we over nighted and replaced the EXV module and had the same EXV failure alarm lockout on power up, immediately after self-test. I deleted the terminal strips at the barrel and the RTAA, same results. WE had between 71 to 76 ohms across bothe EXV's motors ar the "P(34 & 35?)" plug females.
    I then removed all of the EXV cable shield grounds from the RTAA ground screws (the barrel end shield were already taped off)....the unit started and ran fine. We then re-installed the original EXV module...working fine.
    BTW, the RTAA and the EXV's are sourced from the same area and should be at the same ground potential. I'm thinking some kind of weird ground problem impeding the startup "EXV check" procedure.
    The cables are in there own conduit directly between the RTAA and barrel terminal box, so I don't think the shields are necessary. The Trane factory agreed.
    Anybody have any ideas? I know it's fixed, but I don't have a reason why
    jogas
    Last edited by jogas; 04-04-2008 at 04:59 PM.

  5. #5
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    from the Sporlan instructions (i think...can't remember exactly where i got them):

    RTAA EXV Values

    all are +/- 4 ohms
    32F: 33 ohms
    75F: 40 ohms
    148F: 54 ohms


    i do not know at what values the boards detect a "bad" EXV.

    good luck.
    It's tube brushing season...93% done (39.35 miles of tubing)...only 1,242 tubes to go!

    Original member of the Raccoon Brotherhood.

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  6. #6
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    Quote Originally Posted by jayguy View Post
    from the Sporlan instructions (i think...can't remember exactly where i got them):

    RTAA EXV Values

    all are +/- 4 ohms
    32F: 33 ohms
    75F: 40 ohms
    148F: 54 ohms


    i do not know at what values the boards detect a "bad" EXV.

    good luck.
    According to the Trane factory, each EXV's motor should read 75 ohms.
    The Trane SEHI-100 is an OEM style with a site glass built into the side of the valve body.
    jogas

  7. #7
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    I am thinking you are right about different ground potentials, and that is why the shields are only connected at one end to prevent ground loop currents. Were the shields completely isolated from any ground except the ends under the screws? What made you think of removing the shield grounds? (besides trying everything else)

  8. #8
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    Quote Originally Posted by ZZZRSC View Post
    I am thinking you are right about different ground potentials, and that is why the shields are only connected at one end to prevent ground loop currents. Were the shields completely isolated from any ground except the ends under the screws? What made you think of removing the shield grounds? (besides trying everything else)
    Yes, only the ground screws at the RTAA panel. Barrel ends were taped off, and NO CONTINUITY between any of the conductors to it's shield/drain.
    10 years ago, we had a job with Staefa RS Controllers (freely programmable microprocessor) that would intermittently reboot causing a shutdown of clean room equipment. After HUNDREDS of hours, including reprogramming/replacing the RS, we finally disconnected the controllers ground.....never had a reboot occur after.
    So, it kinda surfaced as something to try.
    jogas

  9. #9
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    I worked at a facility that had a a similar problem about 6 years ago and the Trane tech came up with the same solution. I can't remember if it was on a RTAA, but we did replace one about that time. We had a lot of other Trane equipment besides that one. I almost think it has something to do with the shield absorbing or degrading the signals in the line on some things. Was it a Trane cable or one that matched their recommendations? How long was the cable and were the wires in twisted pairs? These seem to be problems that never get identified by the manufacturers and drive the rest of us crazy. I think there is a very simple reason, that everyone (including myself)is unaware of, for the cause of this problem.

  10. #10
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    Quote Originally Posted by jogas View Post
    According to the Trane factory, each EXV's motor should read 75 ohms.
    The Trane SEHI-100 is an OEM style with a site glass built into the side of the valve body.
    jogas
    you are right...my bad. i missed the part where this was a newer unit. my values are for the older style valves.

    good luck.
    It's tube brushing season...93% done (39.35 miles of tubing)...only 1,242 tubes to go!

    Original member of the Raccoon Brotherhood.

    EVERYTHING IS AWESOME!!!

  11. #11
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    Quote Originally Posted by ZZZRSC View Post
    I worked at a facility that had a a similar problem about 6 years ago and the Trane tech came up with the same solution. I can't remember if it was on a RTAA, but we did replace one about that time. We had a lot of other Trane equipment besides that one. I almost think it has something to do with the shield absorbing or degrading the signals in the line on some things. Was it a Trane cable or one that matched their recommendations? How long was the cable and were the wires in twisted pairs? These seem to be problems that never get identified by the manufacturers and drive the rest of us crazy. I think there is a very simple reason, that everyone (including myself)is unaware of, for the cause of this problem.
    The cable used was a Manhattan that was equivalent to the recommended twisted Belden 8719 (I checked). The total run was no longer than 50' (that's being generous).
    I agree with your hunch of signal degradation. When I disconnected the shields and checked their voltage to ground (when the chiller was operating) with my Fluke 87, I was getting pulses up to 250 MilliVolts to the RTAA ground screws.
    We need to remember, the EXV's would pass the service test (long story of factory telling our techs to piggyback and add wire to get past the power-on self test). But would not pass the power on self-test before the chiller even tried to operate.
    So the EXV module check was the problem. When it sent it's own check signal, it must have not accepted the degradation from the shield draining
    the pulses.
    jogas

  12. #12
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    Have had similar problems with other manufacturers stuff and found if you ground the shield/drain on the end opposite the panel, it'll usually eliminate any interference it may pick up. We had a bank with high voltage conduit (4160) running over some chillers for the generators and every time they tested the generators, well I think we just about went nuts trying to find the cause of the shutdowns. Did the above and don't think they ever shutdown again. Have fun.
    We aren't service engineers, we are service re-engineers!! Work is what you make it, have fun.....

  13. #13
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    Quote Originally Posted by the007 View Post
    Have had similar problems with other manufacturers stuff and found if you ground the shield/drain on the end opposite the panel, it'll usually eliminate any interference it may pick up. We had a bank with high voltage conduit (4160) running over some chillers for the generators and every time they tested the generators, well I think we just about went nuts trying to find the cause of the shutdowns. Did the above and don't think they ever shutdown again. Have fun.
    I appreciate the insight, but am perfectly willing to leave well enough alone...unless it rears it's ugly head again.
    Then we will try your barrel-end drain method.
    Thanks,
    jogas

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