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Electric dryer - thermal fuse question

Discussion in 'Electronic Repair' started by Rick, Jan 20, 2008.

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  1. Rick

    Rick Guest

    Hi

    Our Sears electric dryer went completely dead about 2 seconds after
    pressing the "push to start" button. Completely dead - as in no power
    even to the 10 watt light inside the drum.

    I've located a 196 degree thermal fuse in-line to the motor that could
    be responsible for complete power loss to everything 120v if it's gone
    bad. With both leads disconnected I'm getting a reading on that thermal
    fuse that flips between .5 and .6 ohms. (Lowest scale on the meter I
    have on hand is 200 ohms.)

    To my knowledge I should be reading zero ohms if the fuse is good. Is a
    paltry .5 ohm reading enough to indicate that a thermal fuse is bad?

    Thanks

    Rick
     
  2. CJT

    CJT Guest

    Look elsewhere.
     
  3. Ross Herbert

    Ross Herbert Guest

    :Hi
    :
    :Our Sears electric dryer went completely dead about 2 seconds after
    :pressing the "push to start" button. Completely dead - as in no power
    :even to the 10 watt light inside the drum.
    :
    :I've located a 196 degree thermal fuse in-line to the motor that could
    :be responsible for complete power loss to everything 120v if it's gone
    :bad. With both leads disconnected I'm getting a reading on that thermal
    :fuse that flips between .5 and .6 ohms. (Lowest scale on the meter I
    :have on hand is 200 ohms.)
    :
    :To my knowledge I should be reading zero ohms if the fuse is good. Is a
    :paltry .5 ohm reading enough to indicate that a thermal fuse is bad?
    :
    :Thanks
    :
    :Rick


    There is nothing wrong with the fuse then.

    Just try shorting the test leads on your meter and you will probably read
    something like 0.2 Ohms resistance anyway. Unless your meter has a "ZERO Ohms"
    function you can't compensate for the lead resistance.
     
  4. The 0.5 or 0.6 ohms is probably the same reading you get with the probes
    shorted. The fuse should read so close to 0 ohms that your meter won't
    see the difference.

    If the resistance of the fuse really is 0.5 or 0.6 ohms, then there
    is a problem with it. But fuses almost always fail open.

    Or, measure the AC voltage across it when the dryer is supposed to be on.

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  5. Have you tried turning on the dryer again? The fuse might very well read
    close to zero simply because it's reset. If that's the case, then the
    problem is a short further down the line.

    --- the Lady from Philadelphia
     
  6. Jamie

    Jamie Guest

    The protection in your motor is fine, look else where.
    Your meter will not read 0 even if you cross the leads
    unless you have an analog with cal on it.
     
  7. Your meter will not read 0 even if you cross the leads
    Many digital meters have a "zero-cal" pushbutton.
     
  8. Jamie

    Jamie Guest

    REL mode is not accurate.
    As it saids. It's relative and so is the
    same with analog meters.

    for a true accurate reading at low ohms, you
    need a Kevin leaded meter.
     
  9. Rick

    Rick Guest

    Thank you to everyone who replied.

    Regarding the meter situation: If it matters it *does* read zero ohms
    with the leads crossed. It's an inexpensive, $20.00 LCD display type
    meter. I had checked the thermal fuse a few times and it consistently
    gives a reading that hovers back and forth from .5 ohms to .6 ohms each
    time it's tested. (Yes - both leads to the fuse have been removed for
    testing.)

    I think I'm going to bypass it and reapply power to see what happens.
    I'm not looking to start or run the dryer with the thermal fuse
    bypassed. I just want to either rule it in or out - see if the 10 watt
    light inside the drum will come back on (or not.)

    The way I'm reading the wiring diagram for this model - a Sears Ken"less
    these days" - it does not use a drop resistor to supply 120v to the
    timer & motor etc. It uses 1/2 the 240v feed to supply 120v to the motor
    and electronics. And it's also the first time I've seen a dryer put a
    thermal fuse in-line with the motor. (Of course, there is a second
    thermal fuse in the 240v supplied to the heater.)

    The only other thing I can see in the wiring diagram that would kill all
    power to the 120 volt stuff - and make the drum light inoperable as well
    - would be a defective dryer door switch. More disassembly... I'm not as
    inclined to suspect the door switch because, hell, this dryer is barely
    two years old! But with the "quality" of Kenmore appliances these
    days... Exasperating. First the dehumidifier that crapped twice in 15
    months. Now a dryer that went bust in two years. Kenmore? I don't know
    what the hell is going on with Sears, and I thought I'd never say this,
    but Never Again.

    Rick
     
  10. DO NOT DO THIS. You don't know what's wrong with the dryer. The fuse is
    there to protect you and the equipment.

    Start by turning it on and see if it runs briefly as it did before. If it
    shuts off (as I think it will), you can check the fuse quickly to see if
    it's opened. If it has, you know there is some other problem, and you can
    use the schematic to start tracking it down.
     
  11. CJT

    CJT Guest

    A corollary to Murphy's Law is that the component that's hardest to get
    at (in this case the door switch) is the most likely to be defective.

    Find where the wires from the switch go, and check _its_ continuity.
     
  12. radiosrfun

    radiosrfun Guest

    RE: The "Door Switch" - while you might be correct - do NOT overlook the
    obvious. Sometimes it is the simplest of things that goes bad. AND not
    always in the easiest of places to get to!

    RE: Sears - A neighbor of mine - asked me to take him to the store to buy a
    "rototiller" to till some ground for planting. He got the Tiller - brought
    it home - it worked for an hour - then quit. He called them - told them what
    was going on. They told him bring it back. They tried to tell him - he was
    not supposed to use it for the purpose he was - "Tilling". I'm like - what
    the hell do you do with it then, stand it in a corner and stare at it? Any
    "Farmer" would laugh you people out of town - to hear you say that. They
    offered him a cheaper model for the same price - a joke! He told them
    absolutely not. He got his money back - we went a mile out the road to a
    Lowes - where he bought one - and no trouble with it at all. That store - is
    out of business - having gone out about November of 07.

    I have an older dryer my parents bought <new> ($80) in the mid to late 60s.
    Since that time - the pulley had to be replaced twice - the belt 4 times -
    once because the cross arm sort of shifted in time and cut it - prematurely.
    The Pig Tail - once. It still works like a charm! "I" have repaired it all
    but once - my brother in law repaired the first broken belt. That dryer has
    definately paid for itself many times. It was made by G.E. That dryer is a
    120 Volt - 15 Amp Dryer. It has like a 3 hour timer on it. It "does" get
    hot - believe it or not. Unless you overload it severly, the clothes get dry
    in one cycle. My electric bill is only about $40 tops per month - all other
    uses included.
     
  13. Ron(UK)

    Ron(UK) Guest

    One of the most common faults on tumble dryers over here in the UK is
    the door switch or the method of operating same, sometimes a plastic peg
    on the door which can get broken off, or a fitting on one of the hinges.

    That`s where I would start looking

    Ron(UK)
     
  14. I assume you did check the AC outlet or power wiring!

    Also, older installations may have a pair of fuses, on one each leg
    of the 115-0-115 V service. Sometimes, only one of these fuses blows
    (possibly for no good reason) killing power to the 120 V stuff.

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  15. We have a Sear Kenmore from at least 1970, possibly much earlier. (It was in
    the house when we moved in in 1980). It (crossed fingers) has never needed
    service.

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  16. radiosrfun

    radiosrfun Guest

    They had "quality" back then! Better quality, less stringent laws, rules,
    etc... to oversee. I'll attempt a repair at an older item any time. So long
    as the timer keeps working - the rest should be an easy fix for you if it
    goes whacko.
    My mother had a wringer washer - which I used up til about 1999. It finally
    died. Parts were still available - but more than a new washer would cost.
    So, I bought a new "modern" washer. It only lasted 6 years or so. The damned
    transmission went bad in it - cost to replace - $300. Out the door it went.

    TVs used to be good for at least 10-15 years - give or take some
    maintenance. Today - if you get a year out of them, you're damned lucky.

    We have a Big Screen tv at our Fire Department in the Lounge. It is only
    about 3 years old and has been repaired at least that many times - already.
    Not only that - but the damned thing - for being solid state - takes as long
    as a "tube" type TV takes - to come on. That is ridiculous.
     
  17. I'll venture that what you are looking at is not a real thermal fuse, a
    device with a metal link that melts (fuses) when it fails. Those will not
    recover at all after failure.

    More likely what you have is a thermostatic switch that opens a circuit by
    the motion of a bimetal strip. These will recover when cool. Replace it and
    you should be done.

    That would be consistent with the symptoms you have.

    Charlie
     
  18. Rick

    Rick Guest

    We had a Sears electric dryer, circa early 1980's. I replaced the heater
    coil in it once. It then became unrepairable when the motor start/run
    switch cracked in three pieces and Sears no longer stocked the part. The
    only way we could get the switch replaced was to buy a new motor with a
    start/run switch mounted on it. The cost for the motor was $130.00.
    Hindsight being what it is, it would have been a better idea to buy the
    motor than a new Sears appliance.

    Caveat emptor...

    Rick
     
  19. Rick

    Rick Guest

    Thanks Sam

    The AC cord (3 wire setup) and wiring block for continuity? Yes.

    The 240v socket? No. How do you check it properly? 0-115 on both sides?
    Or 115 to 115 for 240 volts? All of the "how to" books avoid the testing
    procedure for 240v outlets and I don't want to do it until I know how to
    do it.

    FWIW it's a dual circuit breaker on the panel. It didn't trip when the
    dryer went dead.

    Rick
     
  20. CJT

    CJT Guest

    Rick wrote:
    Either way. The latter is probably more reliable. Of course, two 115's
    only make 230, but you might have two 120's. :)

    All of the "how to" books avoid the testing
     
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