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  1. #1
    Join Date
    Nov 2005
    Posts
    1,350

    RTAA low evap ref. temp. hair falling out!

    MN: RTAA0804YN01A3D0BD
    SN: U02M07829
    This thing is driving my nuts. Tied into Summit. Continual low evap ref. temp faults, mostly in the winter months. I have done everything I can think of, from checking the charge to replacing the EEV. Has anyone had this problem?

    I get about one fault a month.
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

  2. #2
    Join Date
    Mar 2010
    Location
    Morgan Hill Ca.
    Posts
    1,219
    Quote Originally Posted by allstar08 View Post
    MN: RTAA0804YN01A3D0BD
    SN: U02M07829
    This thing is driving my nuts. Tied into Summit. Continual low evap ref. temp faults, mostly in the winter months. I have done everything I can think of, from checking the charge to replacing the EEV. Has anyone had this problem?

    I get about one fault a month.
    Do you know when it trips? Start up, unloading, loading...etc...

    There are several causes....The EEV is rarely the issue...

    A contaminated refrigerant charge can do this...Has anything been replaced before you R&Red the EEV?

    How certain are you that the slide valve is not sticking?

    Put up some more stats...I love these!!!!


    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  3. #3
    Join Date
    Nov 2007
    Location
    I am unsure myself
    Posts
    1,116
    How is your flow thats where I would start. Sensors and connections next. Does your flow vary possibly under light loads when the air handlers are bypassing. Out there but is your flow switch stuck in the made position allowing the chiller to run with no pump. Only reason I say this is I just found this exact scenario last week. Are you running glycol and have your settings been changed accordingly.

  4. #4
    Join Date
    Jun 2009
    Location
    Florida
    Posts
    540
    I'd concentrate on the slide valve piston. Even if it isn't sticking, it could be loading too fast. Start it up and watch the RLA% in menu 2. If it makes big jumps with each pulse of the load solenoid instead of small incremental increases, then the rings are worn. It would on;y take an hour or so to pull the plate and check. Unthread the nut a little way and screw one of the plate bolts into it. If you're able to easily slide the piston in and out, then the rings are too worn and you need to replace the piston.
    Low Pressure Forever!

    If you know heavy metal, you can work anywhere-Dave Andreson

    Anchors Aweigh my boys, Anchors Aweigh!
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  5. #5
    Join Date
    Oct 2006
    Location
    Central Texas
    Posts
    633
    How cold do you get in the winter? If it happens mainly in this season, it sounds to me like you may be cooling the loop only w/ no load. I agree with Mustardman, what kind of valves do have at the air handlers? You got an 80 ton chiller, does the trip follow one particular circuit? Or does it affect both? I think there was a bulletin out on this, I'll check my books. Hope this can help.
    Sic Semper Tyrannis.

  6. #6
    Join Date
    Mar 2004
    Location
    ottawa canada
    Posts
    2,052
    Water or glycol ??? Is the ucm set up properly ??? Flow,flow ,flow is it primary secondary ,variable etc etc. Dont blame the chiller look at the whole system and as far as the slide valve , yes its a possibility but just check the amps at start up to see if its starting loaded . Maybe the flow drops off too quickly under low load and the UCM doesnt back the chiller off fast enough and bingo she trips .
    The 64 roars to life Whoo hoo ...shes a rolling chassis .
    You bend em" I"ll mend em" !!!!!!!
    I"m not a service tech.. I"m a thermodynamic transfer analyst & strategic system sustainability specialist
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  7. #7
    Join Date
    Nov 2005
    Posts
    1,350
    Quote Originally Posted by txhvac View Post
    How cold do you get in the winter? If it happens mainly in this season, it sounds to me like you may be cooling the loop only w/ no load. I agree with Mustardman, what kind of valves do have at the air handlers? You got an 80 ton chiller, does the trip follow one particular circuit? Or does it affect both? I think there was a bulletin out on this, I'll check my books. Hope this can help.
    I think you may be onto something. There is not a lot of load and there are no valves at the air handlers. The flow stays constant I assume on pressure, 2 chillers in series and vfds on a lead lag pump skid. If there is a bulletin that would be great! Both chillers have had this fault numerous times.

    This is a new contract for our company and the only history I have on it is from the B.E. and the fault logs in Summit.
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

  8. #8
    Join Date
    Nov 2005
    Posts
    1,350
    Quote Originally Posted by graham View Post
    Water or glycol ??? Is the ucm set up properly ??? Flow,flow ,flow is it primary secondary ,variable etc etc. Dont blame the chiller look at the whole system and as far as the slide valve , yes its a possibility but just check the amps at start up to see if its starting loaded . Maybe the flow drops off too quickly under low load and the UCM doesnt back the chiller off fast enough and bingo she trips .
    Good point I will check on Monday. Most people I have talked to about these chillers like them. I don't have a lot of experience with these units so any help is greatly appreciated. Thanks
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

  9. #9
    Join Date
    Jan 2004
    Posts
    1,175
    Also if it starts when OAT is below 50 and it doesn't have VFD on condensor fan it will suck evap down to trip point because of low head pressure.

  10. #10
    Join Date
    Oct 2006
    Location
    Central Texas
    Posts
    633
    Quote Originally Posted by allstar08 View Post
    I think you may be onto something. There is not a lot of load and there are no valves at the air handlers. The flow stays constant I assume on pressure, 2 chillers in series and vfds on a lead lag pump skid. If there is a bulletin that would be great! Both chillers have had this fault numerous times.

    This is a new contract for our company and the only history I have on it is from the B.E. and the fault logs in Summit.
    Ok you're regulating flow w/ the pump vfds, you'll need to determine how the vfd's are throttled. I am assuming they're based on temp rather than pressure, because coils are running wild. Check your minimum speed setting on your vfd's & start there. The Bulletin relating to low evap trips is RTAA-SVB07A-EN, it shouldn't pretain to your chillers since yours are 2002 machines(bulletin for 2001). I don't have it on pdf or I'd post it. My opinion is you've got loop issues too cold temps causing your fault, get some more info on the building, check & make sure your chiller is set-up right. You can set the chillers up on chilled water reset, that way you're not allowing your loop temp to drop too low and fine tune it from there. Hope this can help.
    Sic Semper Tyrannis.

  11. #11
    Join Date
    Aug 2004
    Location
    DFW
    Posts
    147

    RTAA

    Check ucm settings. What is the setpoint? What is the start/stop temperatures. Is it process or comfort cooling? If comfort and below 42 degrees you will see nuisance trips. Fan inverters? Whats the outdoor air temp? Does the chiller have a outside air sensor? Does it have upgraded eproms to control condensor fans better than the previous algorithm? Are the water temp sensors accurate? Water flow ok? Check the IOM for water pressure drop charts. Lots to look at but these are tough machines.

  12. #12
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,374
    Quote Originally Posted by allstar08 View Post
    ...2 chillers in series and vfds on a lead lag pump skid...
    how are the pumps switched? on run hours? on a fault? do they slowly ramp down, turn off, then the other one turns on and slowly ramps up?

    just more to add to your check list
    "Mother" is the name for God on the lips and hearts of children....The Crow

  13. #13
    Join Date
    Nov 2005
    Posts
    1,350
    Quote Originally Posted by acjourneyman View Post
    Also if it starts when OAT is below 50 and it doesn't have VFD on condensor fan it will suck evap down to trip point because of low head pressure.
    There aren't vfds on the condenser fans, just fan cycle controls based on head pressure.
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

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