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Thread: FXVMA Questions

  1. #1
    Join Date
    Aug 2011

    FXVMA Questions

    I have installed over 300 FXVMAs (N2). I am using the FX Builder Application Wizard to generate APDs for terminal boxes. These are mostly fan powered electric heat and cool only vavs. There are over 12 instances where the controller was programmed, commissioned as fully functional, even balanced and days later (sometimes 1 day sometimes 5 or 6) regardless of the APD or box type the Supply Flow will read no value other than 0, causing the box to open fully trying to maintain min cool cfm and thus overcooling the space. The wierd thing is, when it acts like this I upload the original APD, set the setpoints and pickup gain and the box is fine from here on out. This has occured at multiple buildings over the past year. There was one case where I had this re-occur twice and I replaced the controller and its been fine since.

    Balancing is done with the MUI tool. I know its not something the balancer is doing through the tool because some have exhibited this behavior prior to balancing.

    I'm unable to find out why some small portion of these controllers behaves like this after a time period of being functional in the field. Does anyone have any tips, suggestions, or other input? I do have a box in the field today that is exhibiting this activity. I trended supply flow and it just dropped to zero at a certain time and never returned. Meanwhile its overcooling the room and its at 100% open with 1.5"wc in the duct.

    My second question, I have read that people use the JACE as a router to program bacnet devices remotely. Can this be done with N2? Are there any documents or steps to do so?


  2. #2
    Join Date
    Aug 2011
    I should add that cycling power or recalibrating the DP does not help when the controller is reading supply flow of zero.

    When the controller is reading zero in these cases, I am able to measure CFM with a manometer at the flow probe

  3. #3
    Join Date
    Sep 2012
    New York, NY
    I find at times that even though it seems as if the program downloaded properly into the controller, there may have been a curroption while downloading and went undetected or didn't act up at first.
    did you try using CommPro(N2)?

  4. #4
    Join Date
    Jul 2008
    Q1: welcome to JCI ... shame it is near impossible to debug what happens inside an FX controller.
    1 + 1 = 3 ( *** for very large values of 1)

    ...everybody wants a box of chocolates and long stemmed rose

    Be brave. You cannot get eaten by an imaginary tiger.

  5. #5
    Join Date
    Jun 2007
    Are you sharing transformers? If so check to make sure all shared devices are phased the same....

  6. #6
    Join Date
    Aug 2003
    Are the dampers floating if so they could be out of cal if so try cal the units and reset them once a day.
    I have seen this in the past and cal all the box's and then 2 weeks later had the same problem and cal every day and the problem went away.
    also check the timing of pid and motor timing

    hope this helps

  7. #7
    Join Date
    Jan 2008
    Using N2 through a Jace by Tunneling the serial port is tricky. Did work some times, but I got a lot of blue screens. That said, I would not recommend using that.

    Concerning FXVMA, it may not be related to your problem but we had issues with them due to the minimum power supply voltage required.

    We were using too long 24VAC Buses wich lead to a too big voltage drop for devices that were too far away. Those units were cycling, doing strange things, loosing their program, etc.

    Conclusion : instead of using a single 24VAC bus for 1 transformer, use a kind of star topology for your 24VAC supply. No more than 5-7 FXVMA for a 150ft run.

  8. #8
    Join Date
    Feb 2009
    One more thing to look for... Are the flow sensor DPT inputs zeroing to a false value? Or are they zeroing when the damper is open and there is flow? This would cause them to think the flow was zero while the box is open. Try to run auto zeros when the fan is off if there is a period this can happen. For troubleshooting try running the auto zero with the tubes unhooked. then hook up the controller and see if it works. Don't forget the JCI VMA is like boiling water, (watched pot...). be patient whenever trying to watch normal operation. When they are working they work very well.

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