Centrifugal switch on Kenmore dryer motor

Using all the helpful hints I could find on the subject of "Dryer not heating" and checking out all other components it is looking like the centrifugal switch on the motor may be the culprit. Can anyone tell me how to test it? I assume the motor has to be running. Do I take the drum out, remove the belt and let the motor run? I'm assuming that there should be a wire to the heater element that should show voltage only when the motor is running? I'm also guessing that it will only be 120V at the motor. I don't have any diagrams, so if anyone can tell me how to locate the right wire, I will be really grateful. As you can probably see, I'm working at the upper limit of my ability. Unfortunately, I just put a bunch of money in this machine because it is less than 4 yrs old. If I had known that I would have a different problem just a month later ...... well, you all know what I'm saying. Thanks to all. What a great, helpful site!
Ken
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Ken,
Are you sure there is no schematic in the machine? I have always found one tucked somewhere in the unit usually in the top part where the controls are located. It's going to be difficult describing what to look for without specific information on the dryer. Check sears parts website and see if you can at least find a parts breakdown of the dryer, it may lead you in the right direction.
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Eric,
Thanks for your response. I'm at work and the machine is at home, but I'll give it another look. I have checked the Sears site. Unfortunately, their diagrams are not very detailed and somewhat generic. They show a "motor- drive" and a "switch-motor". I guess that is good, since I read one place that the switches are sometimes built into the motors and you have to replace the motor it the switch goes bad. If I find a schematic, how do I test? Do I remove the drum and belt and test the wires leading out of the motor to the heater element? Even if the switch is built in, there should be some wires leading to the element, right? With the motor running, I should detect 120V along that wire, right? If not, is the switch bad? Any advise will be appreciated.
Ken
Eric9822 wrote:

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Ken,
It's hard to say without seeing a schematic. Without finding one or creating one by tracing things out, you are working blind. There are many things that can cause the issue you are having. Checking a switch is best done when the switch is de-energized, out of the circuit, manually activated, using a continuity tester. This may or may not be possible with the appliance you have. If you are working at the upper limit of your capability be very careful poking around energized components.
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The centrifigal switch typically controls the motor start capacitor. If the motor runs but the dryer does not heat, I would look elsewhere. I.e., there are usually several thermostats which can fail, preventing power to the heating element. A simple VOM test will find the problem.
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John Keiser wrote:

Many dryers have a switch for the heat controlled by the motor centrifugal switch. Get rid of the dust and lint around the motor and see if the mechanical part of the switch works. You may be able to replace the switch without replacing the whole motor.
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. I don't

There should be a schematic pasted on the back of the dryer.
Also, it would help if you can give us the model number. There should be a data plate just inside the dryer door.
Trouble could be anything from a bad circuiit breaker (one "leg" open"), bad centrifugal motor switch, bad thermostat, bad wire, or many other things.
If a bad motor switch, it is replaceable w/o replacing motor. See an example: http://www.repairclinic.com/0081.asp?RccPartID 25
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Thanks to all for your replies and suggestions. The model no. is 110. 86870100.
The switch looks exactly like the one at the repairclinic.com link that you sent. On the advice of many helpful folks, I have checked the circuit breaker. I've checked the outlet - 120V on each side. I've checked the thermal fuse, the thermostats, etc. for continuity. I've removed the heater element and wired it to an extension cord and it gets hot. I've checked the timer and it is sending 120V down to the heater. It seems the only piece left is the motor switch, but I'm looking for advice on how to test it. If it only works when the motor is running, do I remove the drum and test it with a voltmeter to see if it is sending 120V to the heater? There are 8 wires on the switch. The wires on no. 1 and 2 are red and much heavier gauge. Since the wires going to the heater are also red and much heavier, I'm assuming that it is one of these two wires. I'm assuming that the wire should have no voltage if the motor is not turning. If the motor is turning and the switch is working, it should have 120V. If the motor is turning and the switch is bad it should have no voltage. Is there another condition where the motor would have no voltage? Am I on track to testing the switch? It's a lot of money to put into a new switch, if the old one isn't bad.
Thanks again to all.
Ken
SRN wrote:

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OK, I just dove in and measured all the wires into the switch, but I'm not sure what it means.
Using the picture at the repairclinic.com link:
With the motor off, terminals 1, 2, and 6 measured 120V. Terminals 3, 4, and 5 measured no V.
With the motor turning, terminals 1, 2, 5, and 6 measured 120V. Terminal 3 measured 40V. Terminal 4 measured no V.
The wires at terminals 1&2 are red. The wire at terminal 3 is purple. The wire at terminal 4 is blue. The wire at terminal 5 is white. The wire at terminal 6 is black. Behind terminals 4 & 5 are two more wires (same color) that lead back into the motor.
Does anyone have any idea if this means anything? Should there be more than 40V at terminal 3? Should terminal 4 measure some V?
If nobody has any advice, it looks like my ever more impatient wife is going shopping for a new dryer and I've wasted $100 + on recent repairs.
Thanks all,
Ken
sargenke wrote:

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sargenke via HomeKB.com wrote:

It doesn't mean too much w/o knowing which wire goes where -- the color isn't necessarily standardized between vendors or even models of the same vendor so that info doesn't help much.
Someone else posted sample diagrams and a verbal description of how the circuit is wired -- using that you should be able to trace your wiring and figure out which terminal is what function.
The way to tell whether the switch is functional is to check continuity (w/o power to the output contacts of course) when running -- they should be open at rest, closed when not.
Certainly a shop should be able to test it for you if you can't. I'm sure these guys fail, but I'll note as a sidelight that I've had dryers run for 20+ years and that has never been a failure mode yet for me...
Of course, if the switch isn't all that expensive anyway, there's the "swap it out and see" technique as well....
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Thanks for the response. Unfortunately the switch is $65-70, so just changing it out is not an appealing option.
I'd like to try to test the switch as you recommend. Are you saying check continuity betwen terminals 1 and 2? How do I get the motor to turn w/o power?
All suggestions are appreciated.
Thanks,
Ken
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sargenke via HomeKB.com wrote:

I don't know that they are 1 & 2 w/o either a diagram or tracing the circuit (I didn't look at what was posted by the other respondent, I'm just talking general testing). What you're looking for are the contacts that complete the power to the heater element (outputs) when the motor is running.
The power to feed the elements isn't supplied through the motor, so it should be possible to run it w/o there being power on the contacts (outputs) to the heating elements. There will, of course have to be power to the motor and it's outputs to the input coil of the relay. But, if you can't trace the wiring and understand which terminals are what, you shouldn't be trying this and ought to either call the service tech back out or take the motor/switch to a service center at let them test it.
Of course, you should be able to simply apply power to the input coils irrespective of the motor running and check whether the output contacts close w/o the motor running at all. Whether it is full 110 VAC input or the 40 V you measured is from an inductive pickup depends on how it is designed or whether you measured something immaterial like a drop across a coil or motor windings or whatever. Since you didn't give any references as to what reference any of the measurements were taken, they're again of little, if any, value.
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It is highly unlikely that a centrifugal switch is your problem. Look elsewhere, and you will find your problem.
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You are not the first to state that this switch is probably not the problem. The only reason I ended up focused here is because it was the only suggestion so far that I could not rule out. If you look at the beginning of the thread, you will see that I have checked the continuity on the various thermostats, the thermal fuse, heater, etc. I have checked for voltage from the timer. I have checked for voltage from the 240V receptacle. I welcome any other suggestions you may have, because I don't want to buy another dryer, but after 2 1/2 hrs at the washateria, wife is growing impatient with my attempts to fix. This might be a dumb question, but could any of the thermostats or the thermal fuse be bad and still show continuity? As a previous urgent attempt, I bit the bullet and purchased a new thermostat - the one in the blower plenum. It mounts on a "heater" (a small black component with a hole in it where the thermostat sits). I purchased a new heater as well. These two components may work together to monitor the moisture in the clothes. Anyways, there was some chat about these being likely to fail and when I examined them there was a lot of what looked like white powdery residue on both components. They both showed continuity, but I was hoping for an easy and somewhat inexpensive fix. No such luck. I'm growing more desperate, so I need your suggestions on other places to check. Many thanks for replying.
Ken
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Yes, the red wire supplies power to the heating element. When the motor reaches speed,it closes the contacts between 1 & 2, and supplies 240V across the heating element.
Did you finds the schematic on the back of the dryer? Here's a sample schematic:
http://i5.photobucket.com/albums/y174/bashful24/Scan10079.jpg
Basically the heater element circuit is a 240V series circuit starting at L1, thru an airtemp selector switch, thru a normally closed limit switch, thru the operating thermostat, thru the high limit T-stat, thru the heater element, thru the motor centrifugal switch contacts between 1 & 2, and completes the circuit to L2, providing 240V across the element.
I have no idea what your troubleshooting capabilities are, so I won't give you step-by-step instructions that might put you at risk for electrical shock.
BTW, I assume you have unplugged the dryer, and used your volt meter on the 250V scale or higher to make sure that you have 240V available at the receptacle across L1 & L2.. If not, you need to do this.
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Thanks for responding. No luck with the schematic. I tried the sears site and they list a wiring diagram, but don't offer it for sale.
I have checked the outlet and I have 240V there.
How do I test to see if the switch is closing at speed? When I probed the switch with my multimeter, I found 120V at both 1 and 2, when the motor was off and when it was turning. Is that normal?
My troubleshooting skills are probably a little above the average homeowner. I have some tools and I'm good at following instructions. I have good mechanical skills, but specialized electrical knowledge is minimal.
As a last resort measure, would a shop be able to test it, if I removed the motor & switch and took it in?
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