how do dryer controls work?

I have a very old clothes dryer, a Kenmore that I'm pretty sure is made by Whirlpool, that has never given me any trouble, and maybe it's time to ask 2 questions about it.
1) The machine has a device to turn the dryer off when the clothes are the desired dryness. You point the dryness knob to the chosen dryness and turn on the dryer. But then the knob rotates and the pointer moves. How does the dryer know where I set it? I can move it clockwise and counter clockwise at any time. Sometimes I've moved it CW to make it stop soon, but if that new position had been the original position, it should have stopped already, and yet it continues to run after I move the knob far clockwise. How does this all work?
2) For the last 40 years, at the laundromat and with my own machine, I always dry clothes on the lowest temperature that is warmer than fresh air. I also usually take the clothes out when they aren't quite dry, so they also aren't really hot yet.
But the air with this machine, even on gentle, must be a lot hotter than gentle. Even after I've opened the machine and taken out the clothes for a few seconds, the clothes seem hotter than gentle. I'm afraid to try the next temp up, because I think that hot air is bad for everything but 100% cotton, and I always have elastic, polyester, nylon, or other fabrics in the load. I don't think I'd be successful trying to measure the air temp, but would you all describe the heat on "gentle" as still pretty hot?
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mm wrote:

With the "auto dry" feature, the timer advances in relation to the demand for heat. The heater has two levels -- on and off. When the dryer starts, the heater is on until the exhaust reaches a predetermined temperature, then the heat stays off until the exhaust reaches a cool point and the cycle repeats. The timer advances only when there's no demand for heat. With a wet load, heat is lost in the moisture, so more heat is necessary. As it drys, there is less opportunity for heat loss.

Is this different from what you experienced before? If the dryer has a switch to select between two or more heat levels, is could be stuck at the hot setting. In some dryers the low setting is determined with a resistor near the thermostat that warms up to "fool" the thermostat into opening (shutting off heat) at a lower temperature.
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I'll have to cogitate on this. :)

No. I should have said that explicitly. It's always been this hot, and as long as I get there, or as long as the dryness setting makes it stop, before it is totally dry, everything is fine. A couple times that didnt' happen, and the clothes would be very hot, and the shirts needed ironing etc. No clothese were ruined yet, but since I no longer iron, I looked pretty wrinkled (until my body humidity and warmth fixed the shirts while I was wearing them (except I don't think I warm the collars.) So I've always thought something might be wrong.

Aha. (Slaps forehead)

Uh-huh.
OK. Now it's on my list to take it apart and check for problems with whatever of these this dryer uses.
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And thanks.
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We have an old Kenmore elec. dryer (circa 1990), and several years ago when troubleshooting and replacing one of the thermostats, I measured the temperatures on the various temp. ranges running the dryer empty. The low temp. had a cut-in temp. of 105 and a cut-out of 157 The med. temp had a cut-in of 107 and a cut-out of 166 And the high temp. had a cut-in of 116 and a cut-out of 169 As you can see, there is hardly a difference.
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You're right. And an incredibly wide range for each.
How did you do it? The exhaust air?
I've been measuring water temp lately with a meat thermometer with a metal probe, but for some reason I didn't think it would work for air.

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Originally, I used a Fluke 52 digital thermometer with the thermocouple wire stuck inside the dryer thru the door. But since you asked, I just went down to the basement and drilled a tiny hole in the dryer duct and used my UEI pocket digital thermometer to measure the temps. again. It's hard to get consistency because the thermostat isn't very precise. On one cycle the cut-in temp. might be 112 and the next time it might be 107. But anyway here is a summary
Hi cut-in 112 cut-out 163 (measured in dryer vent stack) Med cut-in 110 cut-out 156 Hi cut-in 91 cut-out 141
When I used both methods to track temps. at the same time, this time I found the dryer compartment temps peaking much higher than the exhaust vent temps. I assume because the probe inside the dryer was receiving radiant heat energy from the heat element. It peaked at 205 inside and corresponded to a peak of 163 in the vent on high.

the vent pipe and try it.
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Could it be that the air is getting so hot because the exhaust vent is blocked? Not just the accordian hose behind the dryer, but the pipe in the wall. This blockage causes the unexpelled heat to build up.
Alisa LeSueur Certified Dryer Exhaust Technincian http://CleanYourOwnDryerVent.com
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re: Not just the accordian hose behind the dryer, but the pipe in the wall.
Don't forget the ductwork internal to the dryer.
However, clogged ductwork typically prevents clothes from drying due to the fact that the hot moist air has no place to go. That does not appear to be the OP problem.
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