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?