Kenmore Dryer troubleshooting & soldering-iron thermocouple questions - Page 1
Forum section: electronics / beginners

author: edy
author_rank: Super Contributor
timestamp: February 09, 2014, 03:37:05 am
content: Hi folks,I have a Kenmore electric Dryer Model 970-C87902-10 (2008 model) and it is getting VERY HOT on top right rear corner surface and gives a burning smell. My wife pointed it out, she never noticed before. I have cleaned out the duct, lint trap, confirm the blower fan is working (it is physically connected to drum on same motor), etc. Trying some diagnostic tests to figure out what is happening or if this normal operation. Going through diagnostic tests (see manuals and diagrams here:http://www.youserguide.com/wiki/Kenmore_970_C8709).I am trying test 1 showing "H" and control thermistor displayed on digital readout, which eventually reaches a 126 reading. I assume that is the temperature? I am looking at the back of the dryer (in the dark) through a hole and can see the heating element turning on and off periodically, with a little click of a relay as it ramped up to 126.Wiring diagram is here (for electric dryer):http://www.youserguide.com/wiki/Electrolux_134509400efs-007I am assuming the control thermistor is giving feedback to the controller micro and it cycles the heating element on and off to keep the temperature constant. I don't know what the "normal" operating test temperature is supposed to be, but I am up to 131 now after a few more minutes. The heating element is still cycling on and off. The top of the dryer is quite hot. Finally, the cycling stopped, heating element off and it is now dropped back to 128....127...126...125. Maybe it over-shoots during the heating cycles. Top of dryer is not very hot anymore. Seems to heat up significantly ONLY when the heating element is on. It is ranging between 125-133 on average over the long run. So it seems to be working.As I am watching the diagnostic test, I am thinking perhaps it always was this hot but we just started to notice due to the new burning SMELL... hmmm... maybe some lint got stuck on the element and it needed time to burn off. The smell is gone, or perhaps I got used to it. The dryer is not overheating, it is staying within a specified range and operating.Now, I noticed there is the "control thermistor" and also a "high limit thermostat". My understanding is that the control thermistor is what the micro uses to measure temperature directly and turn on/off heating coil, and the high limit thermostat is just a "dumb" safety cutoff in case the temperature ever exceeds some pre-set temperature (not connected to the micro at all).Any thoughts on whether this is normal operation, any advice appreciated.Now for the other quick question, I picked up a multimeter with a K-type thermocouple and was touching it to one of my soldering iron tips to test it out. The reading only got up to about 225 C. That seems to be low, no? Isn't it supposed to be higher? Maybe there was enough air around it and not good enough contact, but I thought soldering irons were in the over 300 C range. Any thoughts? Is it the thermocouple (brand new) or most likely the soldering iron (some generic $10-15 one), or just the contact?

author: wilheldp
author_rank: Regular Contributor
timestamp: February 10, 2014, 01:38:06 am
content: Since your Kenmore dryer was manufactured by Electrolux, let me give you a piece of advice. Throw it away. Immediately. I'm not even close to kidding.All Electrolux dryers produced since 2001 should be recalled as a fire hazard. The blower housing is made of plastic, and the drum is not well supported. The only seals on the drum are front and rear felt gaskets that leak like a sieve. Lint can escape the drum into the housing, and the dryer draws air from the housing, past the heating elements, into the drum. Lint is highly flammable, and so is the plastic lint trap and blower housing. I have personally investigated 200+ fires involving that exact same dryer. It's not a question of *if* your dryer will catch fire...it's a question of *when*.

author: envisionelec
author_rank: Frequent Contributor
timestamp: February 10, 2014, 03:53:17 am
content: Quote from: edy on February 09, 2014, 03:37:05 amMy dryer's element stayed on with an opened door during the timer cycle due to a 'lost' hairpin shorting out the element to the frame. It was extremely hot, smelled burned. I replaced the element and it's been fine since.You can test it by setting a cycle and opening the door. If the element is still red hot (you can usually see it in a darkened room), then there is a short in the element.

author: ConKbot
author_rank: Super Contributor
timestamp: February 10, 2014, 11:30:53 am
content: Quote from: wilheldp on February 10, 2014, 01:38:06 amQuoteseems relevant for some reason

author: wilheldp
author_rank: Regular Contributor
timestamp: February 10, 2014, 12:14:02 pm
content: I guarantee you that Electrolux has spent more money fighting lawsuits over this design than it would have cost them to issue a recall on the defective dryers. I've only been doing this job for 3 years, and have seen 200 of them. I know one guy in particular that has been involved with over 650 lawsuits against Electrolux for the exact same failure.

author: edy
author_rank: Super Contributor
timestamp: February 10, 2014, 12:38:49 pm
content: Thanks for the replies. Any thoughts on how to get into the heating element? I see screws on the back of the inside of the drum. I don't see an easy way to remove the drum from the machine as it is sitting on those felt-matted rings as someone previously mentioned. OVer time due to weight and perhaps humidity the felt warps and you can see where some gaps exist to allow lint into the inside of the cabinet. I had tons of lint inside when I opened it up. No doubt some must have blown past the heating element and if it chars on it, will reduce its efficiency and produce the burning smell. It may also be blocking up holes needed for smooth airflow. If anyone has a manual or link with hints on disassembly that would help. Thanks!

author: wilheldp
author_rank: Regular Contributor
timestamp: February 10, 2014, 04:28:32 pm
content: To open the dryer (assuming your control panel is on the top surface and not the front of the dryer above the door), you just have to stick a flat screwdriver or pry bar between the top and front of the dryer housing. There are two metal clips, one on each side, that you need to pop up, then the whole top will flip upwards. There are then two screws holding the front of the dryer housing on. They are on the inside of the housing about 6 inches down from the top. Remove those, and the front of the housing will fold down. Then you can pop the drum out of the rear bearing and pull it out the front. This will reveal the heating elements behind the drum.

author: edy
author_rank: Super Contributor
timestamp: February 10, 2014, 08:04:54 pm
content: Thanks. My model is the one with controls above the front door on the front panel. It has a LED digital readout and a large knob and lots of buttons to choose settings.I think I need to get the entire front door assembly loosened so that it pops forward, that will release the drum from the felt-lined circle attached to front of the dryer, and I believe there are screws inside the drum on the rear aspect that hold it to the rear heating element spindle with bearings.I'll let you know how it turns out. :-)

author: wilheldp
author_rank: Regular Contributor
timestamp: February 10, 2014, 09:30:32 pm
content: For those models, you remove two screws along the rear edge of the upper panel to remove the top. There are then two screws and two metal clips at the top and two screws at the bottom of the front panel of the housing that have to be removed to allow the front to be removed. After that, disassembly is exactly the same. I can't remember off the top of my head how to access the two screws at the bottom of the front panel. They are hidden by the lower front panel of the housing. When I'm talking these apart, that panel is usually broken since the fires originated right behind it.

author: edy
author_rank: Super Contributor
timestamp: February 11, 2014, 05:54:21 am
content: Hi, thanks for the advice. I managed to take it apart as you can see by the photos. Even more miraculously I put it back together and didn't have any screws left over. :-)I removed even more lint that my initial teardown (which only involved removing top and back access door) managed to get. This time I removed the front door and the drum so I could access the heating element. The bearing at the back had all blackened grease so I lubed that up and didn't manage to find anything too unusual otherwise. Cleaned up the blower, confirmed good air but I suspect maybe something with the duct from laundry room to outside of the house still, so I will have to borrow a leafblower and see if that helps.Idiots who built the house put laundry room about 25 feet and at least 2 bends for sure in the duct inside the wall, because the duct starts at waist level (on second floor) in laundry room yet exists house between first and second floor outside of the house. I used a metal duct (smooth) with 2 bends just to bring it up from the bottom of dryer to the wall waist-height opening, then turn at an angle again to meet the wall duct at 90 degrees. Ridiculous how builders make houses today, especially suburban developments where they are 2 meters apart and packed like sardines, just to call it a "detached house".Sorry, back to the main story... Put it all back and now I am running a light load as I type this post on my BlackBerry which I also took the pictures which I am attaching directly from the phone. The dryer still feels quite hot on top but it does cycle the heating element... I can see it through some holes in the back of the dryer. That means the control thermistor is sending back temperature readings to the micro, which is deciding to turn it on and off. The high temp thermostat has continuity, otherwise it would fail to even turn on the element thinking it was overheat situation. Plus I also tested it with a multimeter.So maybe the thermistor is out of calibration, it takes more heat to bend it and therefore it is getting hotter than usual? Is that a failure mode for this kind of element? Will keep looking into it. I am narrowing it down to either a ventilation issue, or an electrical one. Still not sure which is causing it to run so hot.I tried a thermocouple on the top lid where I thought it gets really warm and I get up to about 75 degrees celsius when the heating element is on. Then it drops back down to about 55 Celsius for a while. When heating element goes on again, back up to 75 Celsius. I am placing the thermocouple on the center of the lid near back, just above where the center of the heating element assembly would be.

author: edy
author_rank: Super Contributor
timestamp: February 11, 2014, 06:13:08 am
content: Not the best contact but I have the thermocouple on top of the dryer where it seems hottest and it cycles between 58 and 76 as you can see in the photo. Definitely hot to the touch. Not sure what normal range is, but this can't be right.Either way, I think this pretty much narrows it to a ventilation issue, not an electrical one. The clothes are still damp hours later, the heater is working and oscillating to keep some range whether it is right or wrong. The only reason the clothes wouldn't be dry is because the humidity is not escaping. Sounds logical? Ergo... Something must be plugging the vent although I already thought I cleaned it out ok, maybe the flaps outside on the hood are partially frozen.

author: wilheldp
author_rank: Regular Contributor
timestamp: February 11, 2014, 12:25:31 pm
content: The ventilation issue is the reason all that lint is accumulating. Because of their design, Electrolux dryers are very susceptible to backpressure in the exhaust system. The installation instructions actually tell you to use an anemometer to make sure that there is no more than 1 in-H2O of back pressure at the exhaust port.I was dead serious that you should get rid of that dryer and get something made by Whirlpool, GE, or one of the Koreans (LG/Samsung). Electrolux dryers are dangerous garbage.

author: edy
author_rank: Super Contributor
timestamp: February 11, 2014, 02:15:51 pm
content: Yes it seems that due to the design, there being only 1 blower actually at the exhaust... Which is responsible for drawing air by suction over the heating element (if the drum is air tight) from air within the cabinet, the heating element and drum with clothes and through the lint trap. Finally air that reaches the blower gets blown out. But when I run the dryer with door open and feel over lint trap, I feel barely any suction. The blower is pushing air out the back theoretically so creating negative pressure which should be sucking air across the drum and lint trap. If there is back pressure due to exhaust being plugged then pressure backs up and restricts air flow through the entire system. It seems a but underpowered to have that little blower. I will keep troubleshooting but thanks for the help.I thought it may be an electrical issue but seems more and more like just bad design coupled with marginally acceptable exhaust even when in pristine conditions. As soon as there is even a small leak in the drum felt lining or restriction in flow the reduction in pressures puts it over the edge. Seems like the system has no tolerance in the design or performance.