Re: Whirlpool dryer heater failure

On 7 Feb, 11:33, "Only Just" <ifixit2@hotmail(dot)com> wrote:
"Seán O'Leathlóbhair" <jwlaw...@xxxxxxxxx> wrote in message

news:6d94b9c9-a762-473c-ac77-ef8faff5d61d@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Feb 7, 12:25 am, Sam Goldwasser <s...@xxxxxxxxxxxxxxxxxxx> wrote:





"Only Just" <ifixit2@hotmail(dot)com> writes:
"Seán O'Leathlóbhair" <jwlaw...@xxxxxxxxx> wrote in message
news:a9e49673-7736-400a-9272-5ab40cbb207e@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Feb 5, 11:27 am, jwlaw...@xxxxxxxxx wrote:
On Feb 4, 6:12 pm, jakdedert <jakded...@xxxxxxxxxxxxx> wrote:

jwlaw...@xxxxxxxxx wrote:
On Feb 4, 1:09 pm, Sam Goldwasser <s...@xxxxxxxxxxxxxxxxxxxx>
wrote:
jwlaw...@xxxxxxxxx writes:
On Feb 4, 10:42 am, jwlaw...@xxxxxxxxx wrote:
My Whirlpool electric tumble dryer AWZ241 has failed. Last
Friday,
the
house's circuit breaker tripped when it was turned on.  After
resetting the circuit breaker and trying the dryer, it did not
trip
again.  The dyer runs but does not get hot.  I guess that the
heater
and / or an internal fuse has blown.
Any other guesses of possible explanations?
Anyone know how easy this will be to fix?
I am not quite sure how old the dryer is.  At least 5 years..
It
came
with an offer of an extended 8 year guarantee but we did not
take
it.
Anyway, it  might be as much as 8 years old.
I have a good collection of tools (including a multimeter),
access
to
a reasonably good spare parts shop, good understanding of
electricity,
and some experience of working of these devices.  For example,
I
have
successfully changed the drive belt of dryers and repaired the
door
switches.  I have not yet had any cause to open up this one..
I just checked the local spares shop.  They could get me a new
element
in a day and it would cost £35.  So, provided that is the fault
and
it
is not too hard to change, it seems worth doing.  Now, I need to
work
up the energy to take the thing apart.
It's very likely the heating element is the problem especially if
the
dryer operated normally the laser time it was used.  Replacement
should be straightforward.  However, it's worth checking the
thermostatsm
and of course for lint buildup which can lead to overheating.

Thanks.  Yes, the dryer was working apparently fine last Thursday.
I
will check the thermostat as well when I have opened it up.  Where
might lint build up except for the filter just inside the door?  I
have already checked and cleaned this.  There was little on it at
the
time of failure, we clean it regularly.

Lint can build up anywhere in the airflow path...significant cause
of
accidental fires.  Check the entire exhaust path, both inside and
external to the dryer.

jak

Thanks again.

I was busy last night and will be busy again tonight but I should be
able to take it apart Wednesday.  With some luck, I will have it
working by the weekend.

Took it apart tonight.  It was easier than I expected.  Unfortunately,
the next step, the diagnosis, was harder than I expected.  So, a bit
of humble pie; I though that understanding the electrics would be the
easy bit.

Three wires: black, red, and brown come from the controller to the
element.  The red and black go to little devices which might be
thermal cut-outs mounted on the side of the element.  If they are cut-
outs then it is a puzzle that they are in both lines.  The outputs
from these devices go the element itself.  The brown goes directly to
the same element terminal as the red indirectly goes.  What's going
here, is the brown a feedback to the controller so that it knows
whether the cut-out is passing current?  But, if the other one failed
it wouldn't know.

Now the real puzzle.  I don't know the power of the element but I
would guess at least 1kW and at most 3kW.  So (at 240V), the
resistance should be a dozen or so ohms.  However my meter thinks the
resistance is infinite even on the 20MOhm setting. So, this would
suggest the element is dead.  However, the meter cannot detect any
voltage between any pair of the red, black, and brown wires.  Surely
there are not two simultaneous faults: the element dying and something
wrong in the controller?  A final explanation is that the controller
runs the motor for some time before sending power to the element.  Is
this likely?  I ran the dyer for about a minute with the meter
connected to the red and black wires.

--
Sean Ó Leathlobhair

The (little devices) are thermal cutouts, they are usually for different
temps being for low and high and have different temp ratings printed on
them, if you only have 1 drying temp 1 could be a safety cutout, if you
have
the 2 temp there is a safety thermo somewhere else in the circuit. also
quite often there is a switch in the motor that controls the power to
the
heater element which may fail at times, they are used so that the heater
won't operate if the motor/fan isn't working ( another safety feature)..
Also
when you tested for power at the element was the timer set at the "Cool
down" position where the motor/fan will operate without the heater to
allow
the clothes to cool down to avoid wrinkling. Having such a high
resistance
in the element indicates the element is faulty tho.
Good luck and leave a message if you still have problems.
(semi retired appliance tech)

Thanks.  I didn't see your reply directly, only as quoted by Sam.

The little devices have what may be part numbers but not obvious
temperature ratings.  They both have a resistance of zero (as fas the
meter can tell).

We tried the voltage test on a variety of settings.  We started new
programs so it should not have been in cool down mode.  Do you know if
the controller may delay the power to the heater until the motor has
been running for some time?  Or might it be clever enough to notice a
problem and cut the power?  The purpose of the brown wire still
puzzles me, it seems to be some sort of feedback to the controller so
it can detect that one of the cut-outs has blown.

A faulty motor sensor makes some sense in the circumstances but it
could be hard to trace without a schematic diagram.  Would it be an
integral part of the motor?

What's the element look like?  A long coiled wire or is it sealed?
If it's just a coil, the failure should be obvious.

Thanks.

Unfortunately, it is sealed in a casing and it is not easy to see the
element directly.  I may be able to open the casing for a look but not
necessarily in a non destructive fashion.  It is held together with
rivet like devices.

Another test would be to hook the element directly to the mains and
see if it started to get hot.  Unless my meter has gone completely
mad, or it is not a simple resistive device, it would seem that it
won't.

So now, the tricky question is whether to buy a new element for £35
without being sure that it will fix the problem.  On the other hand,
it would probably cost at least that much to call out a professional
just to look at it.

--
Sean Ó Leathlobhair

Be careful if you try to power up the heater outside of the dryer as the
outer metal sheath can become live as they often short internally to the
outer sheath as earth.
Look carefully on the inside of the dryer too as sometimes there is a
schematic glued to 1 of the covers, The switch in the motor that operates
the heater etc is usually a mechanical weighted thro-out switch that
operates when the motor reaches a reasonable speed, it can often be seen
inside the end of the motor housing and can be dismantled and repaired. If
dismantling the motor mark the housings well as to relocate them back
EXACTLY as they were.
Hope this all helps anyway.

Thanks for the tip. I don't expect that the element has shorted to
its casing since the casing was earthed and the chassis was not live
and no fuse or trip blew. However, it does not hurt to be careful and
I won't touch the device while it is powered.

Thanks for reminding me to look for a schematic inside the casing. I
have not noticed one but I have not looked thoroughly. I had forgoten
that was a possibility.

Dismantling the motor is moving further out of my comfort zone but if
it gets to the stage that the whole machine may be scrapped then I
will have a go on the nothing to lose principle. It would be a shame
to dump the machine since it is not very old and looks to be generally
in good condition.

--
Sean Ó Leathlobhair
.

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