How does an electric dryers cycling thermostat work?


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Old 06-28-20, 01:36 PM
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How does an electric dryers cycling thermostat work?

I know a person who has a coin operated Whirlpool (unknown model but its from 2008) and the thermostats two outside terminals have continuity and will cut out when heated (I put it on the burner of my electric stove). The two small inner terminals have no continuity at room temp or heated. So how are they supposed to work? The dryer runs just no heat. Also since it is an electric dryer it should be a 240V part? the part says heater 120V

Thanks

I am just the messenger I am not the one actually fixing the machine a friend of mine is.


 
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Old 06-28-20, 01:43 PM
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That thermostat has a 120v heating element in it. That's the two small leads. There is probably a very high resistance on those terminals. The two larger ones are the actual thermostat. Even without the heating element part working..... the dryer will still make heat.

Your problem is not there.
 
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Old 06-28-20, 01:51 PM
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My meter said "OL" when I tried measuring those two small terminals. What is that 120V heaters purpose in the dryers heating circuit?
 
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Old 06-28-20, 02:53 PM
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The heater in thermostat is what opens it. There is no sensor in dryer to tell thermostat to open for a lower temp. They have added a heater in thermostat to fool it. Heat problems are almost always caused by open heater or open thermostat. Not the temp control one. In many years of dryer repair I have not found one bad. dryer is only 240 at heater element. meter will always show 120 unless you are measuring L1 and L2
Your thermostats and heater should show continuity. If open it is bad.
 
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Old 06-28-20, 06:19 PM
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OK I guess the part is good then. Probably a stupid question but if I connect 120V to those center heater terminals how much current should it draw and how hot should it get? Is that even a good idea to test it (I assume not but I'd thought I'd ask before I do that).
 
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Old 06-29-20, 03:35 AM
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Never tried it. the thermostat is turned on by the low heat switch. Like I said before have never found one bad for no heat. Maybe no low heat setting will still get hot.
 
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Old 06-29-20, 04:50 AM
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OL on the meter means the internal heater is open.
Does not mean that is bad as it depends on what meter scale you used. The heaters oar usually in the 5,000 to 10,000 ohm range so you have to use the 20K resistance scale on the meter to measure it.

If there is infinite resistance then it is bad.
But will only effect the lower heat settings so the unit would always run on high heat.

The first thing to check in a no heat condition is the power at the terminal strip in the unit.
L1 to Neutral should be 120 volts
L2 to Neutral should be 120 volts
L1 to L2 should be 240 volts.
Just checking each side to the Neutral for 120 volts is not good enough you must check that it gets 240 volts.

 
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Old 06-29-20, 12:59 PM
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I have an auto ranging multi-meter Sears/Craftsman model 82139.

Anyway that part is good I tested the heater part by connecting a 120V cord and that part got hot and the thermostat turned off.

I told the friend that is fixing the machine that he needs to check for 240V while the dryer is running, I assume the easiest it to check at the terminal block at the back or is there an easier way? the panel is about 100' away

The NM cable is orange in color and he said the jacket said 10/3 w/GND so that requires a 4-wire 14-30R and the matching 14-30P on the dyers end.

So you measure L1 - L2 and you should get around 240V correct and L1 or L2 - neutral or ground around 120V.

I have a hunch that the 240V is somehow missing.

Can you check those thermal cutouts (those one shot ones) in circuit or do you have to disconnect the wires from it. He tested in in circuit and all of them and the element tested good.
 
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Old 06-29-20, 01:18 PM
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Terminal block is the best because it tests the line, the receptacle and the cord.

The thermal cut outs etc. can be tested in circuit but you must use resistance and see close to 0 ohms.



 
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Old 06-29-20, 01:47 PM
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Yes he said everything passed a continuity test, so I guess the 240V circuit is somehow broken. He was measuring the cycling thermostat the wrong way one end prong to a center but as I found out by searching and this forum that they are separate parts.
 
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Old 06-29-20, 05:40 PM
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Do you have a model number for this dryer?
It may be possible to find a wiring diagram.

Usually a dryers heater circuits are wired as
L1
A set of timer contacts. This could be more complicated here because it is coin op.
Thermal cut-off
Operating thermostat
Hi-limit thermostat
Heating coil
Centrifugal switch on the motor
L2
 
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Old 06-29-20, 06:32 PM
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Sorry I don't have the model number all I know it is a Whirlpool coin operated electric dryer from 2008. I agree a model would be helpful but unfortunately don't have that available yet.
 
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Old 06-30-20, 03:34 AM
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Back to basic. Does not heat or dose not run. two different things to check. Coin part does not change how dryer works just how it is turned on.
 
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Old 07-15-20, 04:48 PM
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OK I got the model number now it is a Whirlpool CEM2750TQ2 the dryer runs but no heat. He tested for 240V at the terminal block with the dryer running and the 240V was present (he said it was fluctuating around 243-244V)

I also got the wiring diagram and a parts list they are two separate pieces of folded paper that were jammed behind the control panel.

There are two switches attached to the back of the coin box and the one that controls the heater seems to be bad. The switch has 3 terminals COM NC NO there was only two wires connected to it COM and NO can one of the two different contact circuits go bad?

He connected it to the other side NC and the machine worked (got heat this time) but when the coins were inserted into the coin slot it turned back off instead of on like it is supposed to. However as soon as you plug the machine in it will turn on and run for 60 Minutes (or until a coin is inserted into the coin slot)

That switch is a Greenwald 00-6098 and they have one on order so when they receive the part and the next time he goes back the problem "should" be fixed.

I don't know if I am allowed to post the wiring diagram because I have heard that some of them are proprietary and confidential but I did scan it and save it as a PDF document so if needed I can go back and look at it later.
 
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Old 07-15-20, 05:04 PM
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You may post the wiring diagram here.
What I do when I feel it may be proprietary is post it for several days and then remove it.
 
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Old 07-15-20, 05:41 PM
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Whirlpool CEM2750TQ2 wiring diagram and parts list

OK that is good to know anyway here are those two papers that I scanned into the computer


 
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Whirlpool Part No. 8576821.pdf (192.3 KB, 114 views)
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Old 07-15-20, 05:59 PM
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That is a form C switch. Common - normally open - normally closed.
You need the common and normally open contact. Sounds like it burned open.
A pretty common problem as that breaks the full current of the heater element.

Cherry E14 P microswitch
 
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Old 07-16-20, 10:29 AM
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So it is possible for one of the two contacts to break and not the other side?
I did not know it was switching the full heater current, although my friend said the wires attached to it were very big (low gauge wire) they might have been 12 AWG or 10 AWG wires connected to that switch/
 
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Old 07-16-20, 09:59 PM
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Inside the switch are two fixed contacts..... N.O. and N.C. and one movable one.... C.
So using only N.O. and C could burn the N.O. contact and the N.C. contact would be like new.

If you look at the diagram I posted...... that switch is B. The heat element is switched thru B.
 
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Old 07-17-20, 10:03 AM
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Oh that is cool. I guess I should crack open the defective switch as I never seen the inside of one of these before. If I get the bad switch (if he does not throw it away) I will see if I can open it.
 
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Old 07-17-20, 10:36 AM
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In the mean time..... check out this video.
 
 

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