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  1. #1
    Join Date
    Jan 2007
    Location
    Pittsburgh
    Posts
    181

    Basic Question, I feel dumb asking

    Had a call on an old Carrier RTU about 2 weeks ago, don't know the model # its about 5 ton, built about 1983. Problem was a welded contactor, no big deal, changed it out all checked out. I installed a 30 amp contactor compressor running around 15 amps RLA. Didn't think much about it, this week I get a call, find the contactor I installed totally trashed, the bar and spring between the points laying in the bottom of the panel and points melted to the point of nothing left. The other pole was fine (2 pole contactor), this time I installed a 40 amp square D, mega ohm compressor, its good, power is clean (least while I was there). Thermostat is a digital Honeywell that has a time delay, so I know noone is jamming it off and on. 24 volts coming back on Y1 and 24v @ coil. It does has A CLO card that works, economizer is bypassed because owner does not want to spend the money to fix it, so we know the economizer has no control over compressor, for what its worth..Suggestions please ?

  2. #2
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    HP,AC, or gas pak?

    30a seems kinda light

    what was start up A?
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  3. #3
    Join Date
    Jan 2004
    Location
    mass
    Posts
    534
    single or three phase ? What did disconnect forks look like ? Is time delay the last device before contactor coil?

  4. #4
    Join Date
    Dec 2009
    Location
    Fort Worth, Texas
    Posts
    151
    did you check start and run amps, wouldn't hurt to make sure your not flooding and check wiring from contactor to compressor.

  5. #5
    Join Date
    Feb 2008
    Location
    St. louis Mo
    Posts
    10
    Does it have a saftey board on it? The low and high presure switch and one leg of the compressor goes through a current sensor. I have seen those boards short cycle power the the contactor. Its hard to catch unless you are there when it happens

  6. #6
    Join Date
    May 2004
    Location
    Sunny Mid South
    Posts
    508
    One pole fried...., other not....Sounds like Scott may have a likely cause-don't think I've seen one quite like that....
    -Surf Life Hard!!!-

  7. #7
    Join Date
    Oct 2010
    Location
    Baton Rouge, LA
    Posts
    1,110
    I have been getting a rash of bad contactors recently. They run for a week or two then the coils get weak and start chattering. I am actually replacing one on Tuesday. I got two from Trane on brand new DX systems and one from Baker Dist. (all three replaced at no extra cost or hassle Thank you to both companies) all this month. Might be a common coil maker being used by several contactor companies. Copper is getting expensive you know.
    If you're too "open" minded, your brains will fall out.
    Artificial intelligence is no match for natural stupidity.

  8. #8
    Join Date
    Jul 2009
    Location
    Connectitaxed
    Posts
    2,644
    Possilbe bad contactor coil as previously stated. I might be concerned about installing a 40 amp where a 30 amp ran for years without issue. Could cause more damage than just a contactor.

  9. #9
    Join Date
    Apr 2004
    Location
    Des Plaines,IL
    Posts
    1,012
    Quote Originally Posted by pdrake65 View Post
    Possilbe bad contactor coil as previously stated. I might be concerned about installing a 40 amp where a 30 amp ran for years without issue. Could cause more damage than just a contactor.
    This should not be an issue as long as you have the proper sized circuit breaker/fuse installed upstream of the contactor.
    Stuart
    Lack of airflow destroys compressors.

  10. #10
    Join Date
    Jul 2009
    Location
    Connectitaxed
    Posts
    2,644
    Quote Originally Posted by mcewans View Post
    This should not be an issue as long as you have the proper sized circuit breaker/fuse installed upstream of the contactor.
    Maybe I should clarify my line of thinking with a question to Coolerguy. Did you put a 40 amp in because you didn't have a 30 amp or did you feel that the unit was drawing more amps than the 30 amp could handle and that was the cause for the meltdown?

  11. #11
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,330
    Have you tested the CLO?

    Pull low voltage off term 3. CLO should trip. Check by measuring 24v across term X and term 1. Then put wire back on term 3 and check voltage at term 3 and term 1.

  12. #12
    In the past I installed a voltage recorder

  13. #13
    Join Date
    Dec 2009
    Location
    Bristol NH
    Posts
    229
    If it is 3phase wouldnt a voltage imbalance cause this? Just an idea.

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