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Author Topic: Kenmore 70 series Dryer - no heat  (Read 1503 times)

Offline jj5406

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Kenmore 70 series Dryer - no heat
« on: October 20, 2015, 01:05:34 PM »

So, the high-temp thermal cutout fuse (3977394) on my dryer has blown.  According to my records I replaced it (and hopefully, the  high-limit thermostat) back in August, 2006.  Both the fuse and the thermostat are attached to the heater element canister.  Assuming it was performing its duty properly, the fuse blew because the heater element canister got too hot (presumably above 352 degrees - at least, that number is printed on the fuse), preventing disastrous consequences - yay!

There is a great diagram of the back of the dryer on this forum in a 2009 post at topic 3167:

I've just ordered the replacement fuse and thermostat, but I'm hoping someone can help me understand if the fuse might blow for any reason other than a faulty hi-limit thermostat.  I know regular electrical fuses can blow from a current surge to protect the equipment - but I can't imagine a heat surge (unless there was a fire in there, which it is clear there was not).

The thermostat (3977767), seems to be rated at 221-F (at least that's what it says here:  Which, also according to that page, when operating correctly will cut off power to the heating element until the temp drops by 80 degrees).   Despite the fact that 130 degrees seems like a large discrepancy between the thermostat temp and the cutout temp, I can see how, when working properly, the fuse should blow and kill the power to the heating element if it is getting dangerously hot.

My real question, is:  since the thermostat is supposed to cut power to the heating element at 221-F, is there any reason for the heating element canister to ever reach the cutout temp of 352-F if the thermostat is operating correctly?  Don't get me wrong, I'm absolutely going to replace the thermostat - I'm just wondering if the problem could in fact have been caused by something else, which if not fixed will just cause the same thing to happen again.

I've read about how blockage in the exhaust vent can cause problems, but I don't see how that could directly cause the thermal cutout fuse to blow. Can it?  I noticed that my vent (accordion-style, flexible metal vent) was building up a layer of lint-crud around the interior wall - but it couldn't have been cutting off more than 10% of the cross-section, and the dryer has not been having any issues with getting clothes dry.  I will go ahead and replace the vent too, since it's not real easy to clean and is not very expensive and should make drying a little more efficient and avoid future issues related to vent clogging.  But could vent clogging cause problems that would cause the thermal cut-out fuse to blow if the thermostat were operating correctly?

There were probably about 4 or 5 loads of wash dried in the dryer that day (that's much more the usual 2-4 loads spaced out over a week).  We hire a helper to come once every two weeks to clean the house and she also does some laundry.  And this week there was a load of towels as well as a load of bed-sheets and a few loads of clothes.  Apparently the fuse blew on the last load, which was the sheets.  I assume she knows enough not to put a ton of wet towels in a single dryer load.

Could the amount of drying done all in one day, or a particularly wet heavy load have somehow triggered this problem?  Again, I can see how it wouldn't work well, but I can't see how it would cause the fuse to blow unless the thermostat failed at its job too.

Thanks so much.


Offline andyf80

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Re: Kenmore 70 series Dryer - no heat
« Reply #1 on: October 21, 2015, 08:34:11 AM »
Hi JJ5406,
This is an interesting thread to me and I'll leave it to the true experts to weigh in with some more technical data than I can provide, but did want to mention a shorted heating element.

An often overlooked step in testing an element is to test for a short to ground condition within the heating element. While the element will 'test good'in that the element has not broken and still shows continuity. However, if any part of the element is touching ground the element will stay on constantly instead of letting the cycling thermostat do it's job. This would pop a thermal cutout.
With use the element wire itself gets hot and starts to droop and eventually touches ground.
To test, (with the power off) with your meter on Ohm resistance setting, touch one probe to the element shell and the other to either of the element terminals. You should not have continuity. If yes, the element is shorted to ground.

I hope this helps.
« Last Edit: October 21, 2015, 08:36:14 AM by andyf80 »

Offline bud

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Re: Kenmore 70 series Dryer - no heat
« Reply #2 on: October 21, 2015, 04:58:34 PM »
If the vent is restricted the dryer can not move air through the element and that will cause the high limit t-stat to open. If the high limit doesn't open then the t-fuse blows so that you can correct the problem.
If the load in the dryer was too large, THAT is a restriction.
The door may have been closed enough to start the dryer but not enough to seal the door. That will let the blower draw air from the door instead of air from the element, THAT will cause too much heat to build up in the element and blow the t-fuse. That is also something that you won't find and fix, it will correct itself when you run the next load and shut the door tight.

Drum seals will do the same thing. You will feel lots of air moving from the vent but it's not all coming from the element.

The main thing to check is the element like in the previous post.

If that's good, start looking at door and drum seals and the vent.

Another problem that is hard to find is dryer sheets. They will get sucked up against the lint screen housing and restrict the air. When the dryer stops they fall off.

It's getting colder in my area. Sometimes a cat will sit against the exhaust outside for the warmth and restrict the air, blow the fuse, then the cat is gone, leaving you to wonder why the fuse blew.

I have also found Whirlpool (your Kenmore) has very little play on the temperature of their t-fuses. Very common to blow.

Offline andyf80

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Re: Kenmore 70 series Dryer - no heat
« Reply #3 on: October 21, 2015, 05:07:45 PM »
Thank you Bud!
That is some great info!

The cat scenario made me laugh. Just like a cat.