Archive for January 24th, 2018
Our long-suffering and much-repaired Kenmore clothes dryer didn’t shut off, with the heat on and the timer failing to advance from whatever position we set it to; the clothes were plenty dry and scorching hot. I tried “
timed air dry” to eliminate the heater from the problem and found the timer still didn’t advance.
Referring to the wiring diagram may be of some help:
The timer motor is in the next-to-bottom ladder rung. Its BK terminal on the left connects to one side of the 240 VAC supply and the switch just to its right connects terminal TM to either the neutral AC line (thus unbalancing the 240 VAC line by a smidge) or to through a 4-ish kΩ resistor and the heater element (essentially zero, on this scale) to the other hot line; the resistor thus dropping 120-ish VAC.
The various switches around the timer collect nearly all the wiring in the dryer:
A closer look at the back, minus all the wiring:
The motor comes off easily enough, revealing the fact that it’s not just an ordinary (i.e., cheap & readily available) timer motor:
Hotwiring the motor through a widowmaker zip cord showed it worked just fine. For reference, the upper pinion rotates at about 45 sec/rev, the lower pinion takes maybe 1 hr/rev, both counterclockwise.
Reassembling and hotwiring the complete timer showed it worked just fine, too.
Poring over the wiring diagram suggested the power resistor might be open and, indeed, it was:
The raised zit near the front shouldn’t be there:
Apparently, the resistive element broke at that spot, burned through the thermoset plastic case, and failed safe.
Introducing it to Mr Disk Sander revealed a cavity below the zit, surrounded by the remains of the resistive element:
You can get a replacement resistor from the usual suspects for prices between $20 and $40, plus or minus shipping, but their pictures look a lot like an ordinary power resistor inside a length of heatshrink tubing, rather than the molded OEM part. I don’t put much stock in reviews & comments, although they seemed to suggest you get, indeed, an ordinary power resistor.
I didn’t have a 4.7 kΩ power resistor in my (diminished) collection, so I soldered a giant 1.5 kΩ cylindrical resistor in series with a small 3.5 kΩ sandbox, wrapped them up, and tucked them under the front panel’s ground wire:
A small box of resistors should arrive in the next month and I’ll re-do the repair with a bit more attention to permanency.