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identical failures in two appliances mystery

Discussion in 'Electronic Basics' started by rabbit killer, Oct 23, 2010.

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  1. My clothes dryer is not heating and I found the problem: two normally
    closed thermostats have failed open. Several weeks ago this group helped
    me with my dishwasher which also failed with the thermostat open...

    I replaced the part on the dishwasher and it now works and I could
    replace the parts on the clothes dryer but I'm wondering why these parts
    failed, within several weeks of each other, on two separate appliances.

    Both these appliances are plugged into the same (unnecessary?) GFCI
    outlet in the kitchen and they share the plug with the refrigerator.

    The failed parts are normally closed bi-metallic thermostats wired in
    series with the heating element. The parts are these:

    http://www.alliedelec.com/search/productdetail.aspx?SKU=5570010

    ....for the dishwasher (which I replaced and it now works) and identical
    ones for the dryer except they open at a higher temperature.

    I don't believe this is mere coincidence but I don't know why both
    appliances would fail in identical ways...
     
  2. rabbit killer wrote On 10/23/2010 12:04 AM:
    ....

    I'm not sure now how they both thermostats could fail - they are wired thus:

    power--> thermostat --> heating element --> thermostat --> power


    I don't know how these things fail, but it seems that the first one to
    fail would cut off power to the other and render it safe. But both of
    these are open circuits and I'm pretty sure they are normally closed.

    Could the refrigerator motor be causing voltage spikes when it goes on/off?

    Could the GFCI outlet be the culprit somehow?
     
  3. Tom Biasi

    Tom Biasi Guest

    "rabbit killer" wrote in message
    My clothes dryer is not heating and I found the problem: two normally
    closed thermostats have failed open. Several weeks ago this group helped
    me with my dishwasher which also failed with the thermostat open...

    I replaced the part on the dishwasher and it now works and I could
    replace the parts on the clothes dryer but I'm wondering why these parts
    failed, within several weeks of each other, on two separate appliances.

    Both these appliances are plugged into the same (unnecessary?) GFCI
    outlet in the kitchen and they share the plug with the refrigerator.

    The failed parts are normally closed bi-metallic thermostats wired in
    series with the heating element. The parts are these:

    http://www.alliedelec.com/search/productdetail.aspx?SKU=5570010

    ....for the dishwasher (which I replaced and it now works) and identical
    ones for the dryer except they open at a higher temperature.

    I don't believe this is mere coincidence but I don't know why both
    appliances would fail in identical ways...

    There are just too many variables to make any intelligent hypotheses about
    this condition.
    I think maybe that's what John Fields was saying in his own way.
    Tom
     
  4. Tom Biasi wrote On 10/23/2010 11:33 AM:
    What about the refrigerator on the same outlet? I would think there
    would be internal something-or-other to keep voltage spikes out...

    How do these thermostats fail anyway? All I can guess is too much
    current deforms the bimetallic strip too much and it stays open...

    Can I rule out the GFCI outlet? I don't know how these things work
    internally or how they could change the nature of the power being
    supplied to my appliances.
     
  5. Jamie

    Jamie Guest

    How about if something was wrong with his thermostat controller and
    only the safety over temperature device was doing the regulating, until
    it wore out.!
     
  6. Jamie wrote On 10/23/2010 12:45 PM:
    But for this to happen on two separate appliances (dishwasher and dryer)
    seems unlikely
     
  7. Baron

    Baron Guest

    Its quite common for thermostat contacts to burn enough that they don't
    pass any voltage to the heater, its also possible that the test meter
    doesn't provide enough test voltage to overcome the contact resistance.

    I had an issue with a boiler thermostat a few years ago. No heat ! But
    if you tapped it with a screwdriver handle it would suddenly pass
    current and the heater would work until the next on/off cycle.

    The weird thing was that if you measured the resistance across the
    contacts with the meter, one way round it measured a few ohms but an
    open circuit with the meter the other way round.

    I've seen the same behavior several times with various misbehaving
    switches that have to handle heavy loads.
     
  8. Jamie

    Jamie Guest

    Diode behavior.. Found in galvanic cases..
     
  9. Baron wrote On 10/23/2010 03:20 PM:
    Thanks. I'm just going to replace these parts and hope for the best -
    they are only $12.60 and I will no longer have to haul wet clothes to
    the laundromat...

    rK
     
  10. Rich Grise

    Rich Grise Guest

    Laundromat? Don't you have a clothesline? ;-)

    Cheers!
    Rich
     
  11. Rich Grise wrote On 10/23/2010 05:49 PM:
    Clothesline? I can almost get away with that in the summertime, but I
    live in a damp forest. It's raining now and it won't dry out till May.

    rK
     
  12. Jamie

    Jamie Guest

    And besides, its being reserved for some one to hang themselves, incase
    life gets rough out in that forest, as winter approaches! ;)



    Jamie
     
  13. Rich Grise

    Rich Grise Guest

    Ew. Sorry for that. I grew up in Minnesota; we had a dehumidifier in the
    basement, which we actually didn't need in the winter because the humidity
    has all fallen out of the air in the form of snow. :)

    Cheers!
    Rich
     
  14. shrtrnd

    shrtrnd

    3,824
    519
    Jan 15, 2010
    Refrigerator, dryer, and dishwasher all on the same line, ...
    My experience at my place, is that when you run all those at the same time, you actually get the power wiring to heat up, .... which can trip your thermal protection.
    My advice, unless you want to rewire with larger gauge wire, is to remember fridge is on, and NOT run dryer and dishwasher at the same time, ... you're drawing more current than what your wiring is set-up for. (You can check your service entrance, and
    make sure all you wires are tight on the buss bar, for good connection, ...but ONLY if you know what you're doing).
     
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