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  1. #1
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    Carrier 48TFD008 RTU Fans spinning SLOW!

    Both fans are spinning really slow.One of the compressors has already bit the dust.It was raining when I went there so I was trying to get an idea why these fans are spinning so slow before I go back.Any guidance would be greatly appreciated!

  2. #2
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    Quote Originally Posted by swerve74 View Post
    Both fans are spinning really slow.One of the compressors has already bit the dust.It was raining when I went there so I was trying to get an idea why these fans are spinning so slow before I go back.Any guidance would be greatly appreciated!
    What are the voltages going to the unit?
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  3. #3
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    May 2011
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    Unfortunately,I didn't get that far.Original call was for a tripped breaker and I found the #1 compresor grounded and also a limit on the blower deck had some corrosion causing a fault.As the rain started coming down the owner of the business says,"By the way,I noticed neither fan was turning last week when I was up there".I dashed back up and applied power to unit and observed what he was describing.By that time it was too much rain so I shut her down.

  4. #4
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    Motor master on circuit #1 ?

  5. #5
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    If you reapplied power without disconnecting the grounded compressor and it didn't imediately trip the breaker, the grounded compressor could be completing the circuit for the fan motors to ground. Depending on how the compressor and fan motors are wired, and what part of the compressor winding is grounded, and if it is a 3 phase compressor with a 2 pole contactor.

  6. #6
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    Quote Originally Posted by Dallas Duster View Post
    Motor master on circuit #1 ?
    My first thought too.. Just did a few 10toners where the motor master does both fans

  7. #7
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    Grounded compressor is out of the circuit.It does have a motor master controlling both fans.I am not familiar with the motor master.It is a 3 phase 2 pole contactor and I am reading 118v per.208/230 3 phase

  8. #8
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    Motor master is single phase . There should be a gray sensor coming from motor master that is attached to circuit A coil. You can attach to circuit B .

  9. #9
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    I would have gone w R123s opinion. make sure all the wires taken off the compressor. does sound like a short allowing cirrent to leak somewhere, could even be the motor itself shorted internally, bad capacitor, or windmilling if more than one fan motor in unit.
    Col 3:23


    questions asked, answers received, ignorance abated

  10. #10
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    Thanks for the info guys!! I gather that since the one compressor#1 is responsible for the signal on the motor master head pressure sensing bulb,and this compressor not working,is causing a bad reading back to motor master.Interesting.Thanks again!!

  11. #11
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    Just so you guys know,I did take the grounded compressor out of circuit and moved the motor master sensor to the coil of good compressor and things are working at 1/2 capacity until I can get a compressor in there.Thanks again for all the input!!

  12. #12
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    Quote Originally Posted by swerve74 View Post
    Grounded compressor is out of the circuit.It does have a motor master controlling both fans.I am not familiar with the motor master.It is a 3 phase 2 pole contactor and I am reading 118v per.208/230 3 phase
    That sounds like you are reading from each phase leg to ground. That is not a relevant reading.

    The voltage potential that is of interest to you is the phase-to-phase reading, and not the phase-to-ground reading.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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