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: http://appliancejunk.com/forums/index.php?topic=3167.0
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: http://www.partselect.com/PS351925-Whirlpool-3977767-High-Limit-Thermostat.htm
). 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.