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  1. #1
    Join Date
    Aug 2008
    Location
    mn
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    2

    Carrier RTU Contactor chattering

    We have a Carrier RTU M# 48HJD14-561 we are working on and the compressor contactor is chattering, my tech thinks it is loosing voltage in the econmizer, any thoughts?

    We are mainly a residential shop but am trying to help a customer at his business.

    Nick

  2. #2
    Join Date
    Apr 2012
    Location
    Paper Street Soap Company
    Posts
    2,304
    could be a cut control wire or a cut thermostat wire going to ground somewhere in the unit.

    Could also be a LP or High Pressure switch or the carrier lock out board.

    He needs to isolate each low voltage circuit( Y1, Y2 , R etc )

    Wire around the suspect circuit temporarily to trouble shoot.

    T-stat wires running across the roof or going into a roof access or coming up through the unit are notorious for shorting out.

    If he thinks its through the economizer run a temp circuit around it but through the LP and HP switches to test.

  3. #3
    Join Date
    Apr 2012
    Location
    Paper Street Soap Company
    Posts
    2,304
    Last time that happened to me it was a faulty LP peanut switch.

    Jump each switch just to trouble shoot. He' ll find it.

  4. #4
    Join Date
    Dec 2008
    Location
    Buffalo NY
    Posts
    3,082
    Also try disconnecting your t-stat wires and jump it out. If it is still chattering you know the issue is in the unit.


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  5. #5
    Join Date
    Aug 2008
    Location
    mn
    Posts
    2
    I guess he found a grey wire burnt off on the economizer, he has to try and figure out which 1/4" spade terminal it broke off of?

    Nick

  6. #6
    Join Date
    Jan 2010
    Posts
    6,228
    Should be on the wiring diagram. Located on the backside of the electric controls panel.

  7. #7
    Join Date
    Sep 2006
    Location
    River Forest IL
    Posts
    70
    I've also run into contactors that would just buzz-that is, not pull in-because the transformer was not tapped to the correct primary voltage. Same thing if a transformer doesn't have a high enough VA rating.

  8. #8
    Join Date
    Jan 2010
    Location
    Oklahoma City
    Posts
    170
    check to see if your transformer is connected to the 208v or 240v tap if it a 208/240v unit. They come from the factory on the 240v tap and if you have 208v it can make the contactor chatter.

  9. #9
    Join Date
    Sep 2007
    Location
    NH
    Posts
    1,147
    On some of those old Carriers they broke the freeze stat through the common leg to the contactor coil... Thats what it was last time I had one doing that. Little confusing when you jump 24V from the transformer right to the coil and it still does it.

  10. #10
    Join Date
    Jan 2010
    Posts
    6,228
    [QUOTE=Dchappa21;13246951]On some of those old Carriers they broke the freeze stat through the common leg to the contactor coil


  11. #11
    Join Date
    Jan 2010
    Location
    Oklahoma City
    Posts
    170
    Quote Originally Posted by Dchappa21 View Post
    On some of those old Carriers they broke the freeze stat through the common leg to the contactor coil... Thats what it was last time I had one doing that. Little confusing when you jump 24V from the transformer right to the coil and it still does it.
    And they ran the wire over the blower bracket between the top of the unit and the bracket. After a while the insulation on the top goes then the wire insulation and a nice short to ground on the transformer that comes and goes with vibration. Found 4 of these on one roof.

  12. #12
    Join Date
    Apr 2007
    Location
    Pa
    Posts
    758
    check for a time delay. that has done it to me many times

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