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  1. #1
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,356

    welded contactor

    Went on service call Friday. Found compressor contactor welded shut. This was compressor #3. This is a four circuit 3 phase 460v Rheem. Ohmed out everything, checked voltage, checked wiring. Everything looked good so I replaced contactor. Compressor ran good. Checked voltage, amps, and pressures-all ok. The weekend on call tech called me and said he went there (less than 24 hrs later) and its welded again. Also tripped ground fault in mcc room. Plant electrician assured him ground fault will only trip when 277v or greater is detected to ground. Our on call tech said he wanted to replace compressor. Any thoughts?

  2. #2
    Join Date
    Nov 2004
    Location
    up in the hizzy
    Posts
    1,386
    rooftop unit?with economizer?

  3. #3
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,356
    Package unit set on the ground. Side discharge. No economizer.

  4. #4
    Join Date
    Apr 2004
    Location
    Des Plaines,IL
    Posts
    1,016
    Check internal wiring of compressor.(Voltage selection)
    Stuart
    Lack of airflow destroys compressors.

  5. #5
    Join Date
    Jul 2012
    Location
    Southwest
    Posts
    114
    Megaohm it, then probably replace it.

  6. #6
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    did you replaced contactor with correct one?
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  7. #7
    Join Date
    May 2002
    Location
    evansville indiana
    Posts
    943
    I've seen this before when something in the safety circuit or control circuit causes that contactor to "chatter" . iE a loose connection etc...

    You may have a failed compressor now but I would be cautious as you may have a failed new compressor later .

    A TDOB , delay, ahead of the contactor may be cheap insurance here until whatever is causing this rears its ugly head full time.

    This is my theory ,its okay to disagree with it..... I'm still in this game after 25 years and its not because I'm a dumbass
    mikeacman

  8. #8
    Join Date
    Sep 2011
    Location
    Vancouver, WA
    Posts
    259
    Had the same problem with a 10hp blower motor last year. It was 460v and found the contactor welded. It did this several times before I parked my asp on a bucket and spent a few hours watching it. Nothing happened till I was putting the cover on the electrical box and there was a loud noise and then quiet as the unit shut down. Checked the motor contactor and found it welded. Checked the motor windings for a short to ground and line to line, nothing. Since this was the third time I replaced the motor and contactor and have not been back since. What it sounds like is you are having is an arc flash fault. Replace the compressor.

  9. #9
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,356
    Quote Originally Posted by dandyme View Post
    did you replaced contactor with correct one?
    Yes. Within specs of oem.

  10. #10
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,356
    Thanks for the input. We are going to replace compressor. By the way it megged ok. I will update post when results are in.

  11. #11
    Join Date
    Jun 2010
    Location
    Miami
    Posts
    258
    FWIW, ground fault relays do not work by measuring voltage or currennt to ground. If fact they don't need nor reference ground at all.

    On a normal 120 VAC outlet they look to see phase and neutral current are equal. If not they assume the differnce is going to ground and trip. On poly phase circuits they look to see that the vector currents of the phases (and neutral if used) sum to zero. So...uh....don't trust that plant electrician too far

  12. #12
    Join Date
    Mar 2007
    Location
    South Texas
    Posts
    217
    Had similar problem, Rheem unit with 4 compressors set up for 2 stages, thermostat 150 ft run. When contactors pulled in they chattered, especially if calling for both stages, low voltage dropped to below 22 volts. No control board in unit ended up installing isolation relays for Y1 and Y2 to keep control voltage from dropping so low. Took care of issue

  13. #13
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,639
    I'd bet it's in the low voltage circuit
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

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