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Thread: Blowing fuses

  1. #1
    Join Date
    Sep 2003
    Location
    Western PA
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    Blowing fuses

    Carrier RTU model# 48TFE012, serial# 4803G20688.
    From what I gather from the owner, one fuse in the dissconnect is blowing towards the late afternoon. I know from previous PM's that this unit has been running high head pressure, especially second stage. Other Techs have been there and replaced the fuse. The owner was told by one Tech to direct a lawn sprinkler at the condenser. He stated to me that he did and the fuse problem went away. We have also known from PM's that the blower motor had bearing going bad. He had us replace the motor thinking that was the cause of the fuse blowing. I'm not sure if we sold him on that one or if the owner thought that that might help. Well after we replaced the blower motor, he says he did away with the sprinkler and the fuse started blowing again. Now i got called to the job. I'm at least the third Tech involved so I what to get this corrected.

    I'm suspecting that the second stage circuit is over charged and causing the compressor to run at high amps therefore blowing the fuse. Does this sound possible, or should I have a few more beers and rethink this thing.

    Here are some numbers that I gathered on Friday.
    Ambient 76

    Circuit#1
    68psig
    40 temp
    58 line temp
    18 superheat

    230psig
    112 temp
    82 line temp
    30 sub

    return 72
    supply 65

    compressor#1 rated amps 15.8
    actual amps 14.7

    Circuit #2
    77psig
    45temp
    48 line temp
    3 superheat

    270psig
    124 temp
    95 line temp
    29 sub

    compressor#2 rated amps 15.8
    actual amps 16.6

  2. #2
    Join Date
    Oct 2003
    Location
    South Carolina
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    1,241
    Check the wire connections at the fuses first. Sounds like something is loose that doesn't trip the fuse until it's been operating for awhile.
    “Two things are infinite: the universe and human stupidity; and I’m not sure about the universe.” —Albert Einstein

  3. #3
    Join Date
    Oct 2001
    Posts
    6,966
    blowing the one fuse is a giveaway it isn't anything in the unit you need to change the style of the fuses(all 3)that head seems hi for the ambient and the amps are way up.check those contactors for burn/arc'g...short cycling will pop a single fuse but not blow 2 as a shorted item...that water spraying might a caught a condenser motor possibly.but go with the short cycling and more of a time delay on those fuses
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  4. #4
    Join Date
    Apr 2007
    Posts
    16
    Had the same problem 1 month ago. Tightened all wire connections, still blows one fuse (on a 3 phase unit). Amp draw is well under nameplate amps, but the fuse heats up sooo hot. The fuse never really blows, just burns out. Then the main breaker blows. The disconnect has loose or corroded contacts. You can't clean it, just replace the disconnect, problem go bye bye.

  5. #5
    Join Date
    Jul 2008
    Location
    ATL
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    56
    how is your power thire is possitbly droping in afternoon due something they have added to this buss do you have something to trend your voltage to see if it is on the line side.

  6. #6
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    Western PA
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    Quote Originally Posted by Kraeusen View Post
    Had the same problem 1 month ago. Tightened all wire connections, still blows one fuse (on a 3 phase unit). Amp draw is well under nameplate amps, but the fuse heats up sooo hot. The fuse never really blows, just burns out. Then the main breaker blows. The disconnect has loose or corroded contacts. You can't clean it, just replace the disconnect, problem go bye bye.
    The disconnect was installed with the unit in '03 I believe. I checked the connections and found none loose or corroded.

  7. #7
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    Jan 2008
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    Dallas ,Texas
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    Has anybody split the condenser coil and cleaned it?
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  8. #8
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    Quote Originally Posted by thegoodlistener View Post
    Has anybody split the condenser coil and cleaned it?
    I was waiting for someone to ask that. Two months ago during a PM, I found the condenser coil was dirty. I cleaned the coil but did not split the coil. Carrier's instructions tell you to split the coils for cleaning. I've been told in the past that its not necessary.

  9. #9
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    Quote Originally Posted by targetman View Post
    Carrier's instructions tell you to split the coils for cleaning. I've been told in the past that its not necessary.

    carriers instructions are correct.lol you NEED to split condenser coils to clean them. carriers are easy to split and clean, it should only take 20 minutes to actually clean and split after your hose is run to the roof.

    you have a problem looking right at you. your already overamping the second stage compressor at 76 degree outdoor temp. look at the discharge 270 at 76 degrees!. Start with that second stage and go from there.

  10. #10
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    Western PA
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    Quote Originally Posted by y7turbo View Post
    carriers instructions are correct.lol you NEED to split condenser coils to clean them. carriers are easy to split and clean, it should only take 20 minutes to actually clean and split after your hose is run to the roof.

    you have a problem looking right at you. your already overamping the second stage compressor at 76 degree outdoor temp. look at the discharge 270 at 76 degrees!. Start with that second stage and go from there.
    My first thought was that the condenser was still dirty and needed to be split. But trying to convince the Service Manager is a differant story. So the hell with it. I had talked to the owner on Friday about doing just that but was called away by SM. It wouldn't be that hard to do on this unit, it's on a pad with a hose nearby. I,m sure I'll get sent back. If they sent the Tech who replaced the blower motor, he would be charged with a call back. And if he gets charged with a call back, that would hurt his chances of employee of the month.

  11. #11
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    Jun 2005
    Location
    The Gray Northwest
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    661
    High SC and low SH on circuit 2 plus the fact that putting a sprinkler on the condenser keeps the fuse from blowing indicates a mechanical problem, not electrical IMHO.

  12. #12
    Join Date
    Jun 2008
    Posts
    41

    Split the coil

    you'll be surprised what you find in between. I've had a few that look clean from either side but caked on the inside. You're pressures and amperage are pointing to that as well. Sprinkler on the condenser is only masking the problem and just confirms that'...if it was electrical or otherwise the sprinkler wouldn't make a difference.

  13. #13
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    Make sure you zip tye that coil back together so it doesn`t rub a hole in it at a later date.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

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