McQuay RPS intermittent failures to start
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  1. #1

    McQuay RPS intermittent failures to start

    Has anyone had problems with units attempting to start and then resetting in as soon as the contactor pulls in? Or the contactor chattering on start and then failing to start.

    I have been looking at the relays and timers, but nothing is consistent. So I cannot identify the problem.

    I hate to start parts changing!

  2. #2
    Join Date
    Aug 2010
    Location
    N.E Ohio
    Posts
    15
    If you give complete M# and S# will know what type of controls are in it. Most likely bad
    output board relay if it is that vintage.

  3. #3
    Join Date
    Feb 2011
    Location
    Indianapolis
    Posts
    5
    Quote Originally Posted by Zuni View Post
    Has anyone had problems with units attempting to start and then resetting in as soon as the contactor pulls in? Or the contactor chattering on start and then failing to start.

    I have been looking at the relays and timers, but nothing is consistent. So I cannot identify the problem.

    I hate to start parts changing!
    I have the same problem with a York YCA440, Ive changed the High pres switch,control relay, and relay output boards and contactors. Still shuts down as soon as it starts on Current/HP alarm. Ive even changed the CT mod. I had York come out and they cant figure it thats when we started parts changing.

  4. #4
    Quote Originally Posted by referman10 View Post
    I have the same problem with a York YCA440, Ive changed the High pres switch,control relay, and relay output boards and contactors. Still shuts down as soon as it starts on Current/HP alarm. Ive even changed the CT mod. I had York come out and they cant figure it thats when we started parts changing.
    Check is the rate of contactors coils voltage are correct for the application in some cases factories load units with the wrong components. also contactors itself they could come defective from factory.
    Do this desconect the coil for one of the contactors and see what happens if the problem continues conet thatone back and do the same with the other one. if the problem continue check voltage going to your coils if 24, 110, or 208 or so and see if they match it up with whatever your contactor says.
    This is what i mean.
    One time i spent a full day trying starting a unit brand new, i`m not gonna mention brand name ok but, after spending creazy time there i noticed that the voltage for the unit was 208 v but my compressors were 460v.
    noway this compressors would run, hey idf was runing also condenser fan were runing

  5. #5
    Zuni I think i answered you quetion to somebody el by mistake

  6. #6

    Model and Serial for Mcgushvac

    Thanks Mcgushvac,

    Model# RPS090CLA
    Serial# FB0U010300231 02

    I thought about someone else was saying and disconnecting the coil on the contactor, checking voltage there and see what happens.

    I was wondering what I might see if I disconnect the load side of the contactor and see if it does the same thing with no load.

  7. #7
    Join Date
    Feb 2011
    Location
    Indianapolis
    Posts
    5
    I think that disconnecting the load side is a great idea, I will try that next week and post my results. Like the other guy, its not consistant. This is the kind of stuff you go home with at night, makes you crazy!

  8. #8
    Join Date
    Feb 2006
    Location
    SouthEastern Virginia
    Posts
    1,075
    I had a Trane Self Contained unit that I was starting up years ago. As soon as the compressor contactor pulled in, the lockout relay tripped. After much struggling, I found that the impact of the contactor pulling in was causing enough vibration to trip the reset relay. I removed the reset relay from the panel and let it float. No more lockout!
    It might get loud!

  9. #9
    Join Date
    Feb 2011
    Location
    Boston area
    Posts
    1
    Is this MT2 or MT3? What are the timers setting? Timer settings, 180 sec for startup, recirc, & lowtemp. 30 Sec Flow. there are others but not important at this time. If the airflow timer is at 0 then the unit will go into restart as soon as it starts. Does the controller reset turn off & back on or does it just go into restart on the display? Are there VFD's? Have you called Mcquay and talked with Brad?

  10. #10
    Join Date
    Sep 2004
    Location
    Kansas City, Kansas, United States
    Posts
    13,817
    I work on hundreds of RPS units!
    Had every problem in the world!
    The only time I ever had a unit that did this was a problem with high duct static switch, freeze stat and ofcourse the overloads!

    what kind of controls are on this thing?
    w-7100 controller, microtech, what operates the duct static?
    VFD, IGV pneumatics or DDC?

    just wondering?
    I am not a mcquay mechanic and do not know serial number???????

  11. #11
    Join Date
    Nov 2009
    Posts
    11
    Did you ever find a solution to the outputs chattering?

    I'm having a very similar issue. I have a RPS090CLY equipped with VFDs on the supply and return fans. Occasionally the supply and return fan contactors would chatter and lock the unit out on a fan failure alarm.

    I've been through everything on the control circuit for the fans

    - Went through the complete start / stop circuit from the output board to the fan contactors. Every connection was good and tight.

    - Fan contactors have been replaced

    - McQuay output board has been replaced

    - Relays that plug into output board have been replaced

    There isn't much left here to go wrong. I'm leaning towards the Microtech control board. It's a very basic circuit to pull in the fan contactors. I'm getting very frustrated with this unit as well as my customer. Any ideas would be greatly appreciated.

    Thanks,
    Mike

  12. #12
    Join Date
    Mar 2007
    Posts
    3,103
    Have you checked the 5 amp fuses on the output board or the MOVs on the back of the output board?
    "There is no greater inequality than the equal treatment of unequals."

    -Thomas Jefferson

  13. #13
    Join Date
    Nov 2009
    Posts
    11
    Fuses are good. What do you mean by "MOVs"?

    Thanks

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