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Motor capacitor problem.

zorbazorba Senior MemberPosts: 23,844 Senior Member
edited November 2018 in Clubhouse #1
I know pretty little about motor capacitors, and I think I have a bad one. That's not really the problem, troubleshooting the circuit its in is...
The cap, a 15uf, measures about 2K ohms with no reactance as shown on an analog meter.
However, before I buy another one, I'd like a little more info on the motor circuit. This is the compressor motor of a dehumidifier. 3 wires, white (neutral), red, and blue. The red wire feeds power to the motor, and it is hot with regards to the neutral. The blue wire goes from the motor to the high side of the cap, then disappears into a wiring harness headed for the control board.
I'm not seeing any voltage on the blue wire at the top of the capacitor. Should I? I'm thinking I should, and there's a problem in the control board - but I'm seeking guidance as I've never worked on a motor circuit before.
-Zorba, "The Veiled Male"

"If you get it and didn't work for it, someone else worked for it and didn't get it..."
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Replies

  • zorbazorba Senior Member Posts: 23,844 Senior Member
    #2
    Ok - then I'll get the $5 part and see what happens. You know more about this than I do! Thanx!
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
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  • tennmiketennmike Senior Member Posts: 27,444 Senior Member
    #3
    What CPJ said. The type capacitor depends on whether it's a start capacitor or a run capacitor as to whether or not you see voltage across the capacitor.
      “I refuse to answer that question on the grounds that I don't know the answer”
    ― Douglas Adams
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  • zorbazorba Senior Member Posts: 23,844 Senior Member
    #4
    Yea, I did some Google-Fu - I'd think there'd be voltage there when the motor isn't running, but "whatever". $8 gamble for a $150 machine.
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
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  • pjames777pjames777 Senior Member Posts: 1,421 Senior Member
    #5
    Digital meters, many have capacitor testing on them now for a modest price.  Ditch the analog and self troubleshooting will get easier.  Run capacitors are never open, Start capacitors with internal switch maybe.  Most run capacitors are low mfd, run capacitors usually are high mfd
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  • FisheadgibFisheadgib Senior Member Posts: 5,797 Senior Member
    #6
    I'm kinda confused about what your calling the "compressor motor". Is it the compressor, or the fan motor?
    snake284 wrote: »
    For my point of view, cpj is a lot like me
    .
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  • FisheadgibFisheadgib Senior Member Posts: 5,797 Senior Member
    #7
    Thinking about it, 15 mfd in that could only be the compressor and nothing should be showing any voltage with the unit unplugged. To test the compressor windings unless the terminals are labeled differently the standard configuration is the common lead in the middle, the run to the right, and the start to the left. First, no terminal should show anything to ground, then check resistance between common and run, then between common and start, and between run and start. The values from c and r added to c and s should total the resistance between r and s. There is also the posibility of a mechanical failure but you would need an ampmeter to determine that. If it's not the cap, buy a new unit.
    snake284 wrote: »
    For my point of view, cpj is a lot like me
    .
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  • zorbazorba Senior Member Posts: 23,844 Senior Member
    #8
    Fisheadgib said:
    If it's not the cap, buy a new unit.
    That's the bottom line - but there's only 3 wires disappearing into the compressor motor, no right, middle, left, just red, blue, and white. Blue is the start as it's what goes to the cap - but I kinda thought that there'd be voltage on it if it wasn't running.
    Cap will be here Friday.
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
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  • pjames777pjames777 Senior Member Posts: 1,421 Senior Member
    #9
    zorba said:
    Fisheadgib said:
    If it's not the cap, buy a new unit.
    That's the bottom line - but there's only 3 wires disappearing into the compressor motor, no right, middle, left, just red, blue, and white. Blue is the start as it's what goes to the cap - but I kinda thought that there'd be voltage on it if it wasn't running.
    Cap will be here Friday.
    Most likely a run capacitor. Schematic should label it as such.
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