Dryer Repair: The Drum’s Not Tumbling Part 2

Dryer Repair:  The Drum’s Not Tumbling – Part 2.

When we left you we had covered the most likely causes of the drum not turning.  Those were also the easiest for you to diagnose and repair.  They were:

The Door Switch

The Belt

The Idler Tension Pulley or Roller (spring)

This time we will cover some of the more technical culprits such as the motor, timer, and the push-to-start switch (although the push-to-start switch is an easy check).

1.  The motor.

This is where you will need a wiring diagram and a good knowledge of your handy dandy multi-meter.

If the motor is bad, it will have to be replaced.  If that is the case, then shop around for the best buys.  I would not recommend a used one unless the parts distributor gives you some sort of warranty.  The warranty might consist of simply swapping the motor out until they find a good one, but I would recommend at least a three month warranty.  If it lasts three months, you’ll probably get a good year or two out of it.

These motors are expensive  – 100 to 300 dollars, so I want to warn you up front.

The motor has a “start” winding and a “run” winding.  Because the “run” winding can not handle the load of starting the drum with its heavy-wet clothing, a “start” winding is incorporated in the motor body.  With the two windings working together the motor is able to turn the drum.

Built into the motor (this part is sometimes replaceable) there is what is called a centrifugal switch or motor switch.  When this motor is sitting still and no power is applied to it, the switch is in a “closed” condition.  This allows power to hit the start winding and start the motor spinning.  When the motor gets up to speed (in seconds) the centrifugal switch “slings” open and opens the contacts to the start winding – taking the start winding out of the circuit.

This cycle will continue as the drum slows down and speeds up (you will not notice this change in speed).  When the drum slows down, the centrifugal switch will close sending power to the start winding and kicking the motor up to speed again and again and again.

Many of the dryer motors use a capacitor that is usually mounted on the side of the motor.  This is usually replaceable. It helps the motor overcome the load of the start-up by literally jolting the motor into operation.  It is constantly charging and discharging causing the motor to maintain speed.

Some dryer motors have a thermal switch within them that causes the motor to shut down when the motor gets too hot.  Thermals that reset themselves when the motor cools are usually good for only a few breaker actions.  If the reason for the overheating is not taken care of, they will eventually open permanently and the motor will have to be replaced.

To check the motor, motor switch, and capacitor, you will need to access them by removing panels.  This will be up to your ability to figure out how to do that…just remember…they go back the opposite way you took them apart.

Before you read any further, WHAT DO YOU DO FIRST? Kill the power by unplugging the dryer.

Looking at the wiring diagram find the drive motor.  It will usually be a circle with at least three connections going to it (A wire to the start winding.  A wire to the run winding.  A wire known as the common).  Inside the circle you will see the schematic symbols for the start and run coils of the motor.

By noticing the wire colors or numbers you can tell which connections go where.  DRAW A PICTURE OF WHERE THE WIRES GO! Remove those wires going to the common, start, and run winding.  With your multi-meter set to read continuity (resistance or ohms) place the black probe on the motor connection labeled “comm0n”  – “Com” – or “C”.

Take the red lead and touch the connection marked “start” or “S”… If no reading, the winding is open or the centrifugal switch (start switch)  is bad.  If you get a reading, then the start winding is probably fine.

Now, remove the red probe and place it on the “run” connection or “R”… If no reading, the winding is open and the motor is bad.

Note: If the thermal fuse or breaker is bad, you will not get a reading either.  If this component is built into the motor then the motor will have to be replaced.  Make sure you take the model and serial number with you to the parts distributor.

On some motors, the start switch is replaceable.  It is usually a black plastic box looking device mounted on the back or front of the motor.  A quick way of checking the motor start switch is to depress the little red or orange activator.  If you hear a click then it is probably good.

The motor bearings can also go bad. A dryer with a motor in this condition can sometimes be started by hand and it will run.  However when the motor gets hot the bearings begin to seize and the motor will stop. In this condition you must also replace the motor.

To check for a bad motor bearing, remove the belt from the motor drive pulley.  If you can grab the shaft end/pulley end and move it up and down or left and right, the motor bearings are worn, and the motor will have to be replaced.

To replace the motor, make your drawing of the wire locations, remove the belt, and remove the hold down brackets or bolts.  Just go in reverse to replace it.

2.  The Broken Belt Switch.

I added this one because some dryers use a device to shut the motor down if the belt breaks.  This switch can usually be found by following the wire coming off the common of the motor.  It will have at least two wires, and will be located somewhere in the path of the belt.

This switch can be checked by continuity.  Place your probes of your meter on the two connections COM and NO with wires removed.  Manually activate the switch by depressing the plunger button.  If you get a reading, then the switch is good.  No reading… the switch is bad.  Replace.

Of course, if the belt is broken then the switch will deactivate and shut the motor off.  Replace the belt according to previous posting.

3. The Push-to-start button/switch.

This switch is located in the control panel.  After you unplug the dryer, open the control panel and you can access the switch.  Again, this switch should have COM, NO, NC designations on it.

With your meter on continuity, place the black probe on the COM connection, and the red probe on the NO connection.  Activate the switch by either pushing it in or turning the knob.  If you get a reading when activated, the switch is good.  If you do not get a reading, the switch is bad.

4.  The Timer.

Please do not try to take the timer apart.  You will never get it back together again!

The timer is located in the control panel, or control head.  You will have to gain access to the timer by taking the back off the control panel.

The timer  is the source for power to the motor and if the timer contacts are defective, there will be no power getting to the motor. Since the wiring is different between brands and models, you will need to refer to your wiring diagram for terminal locations.

WARNING! You will be doing this check with the power applied to the dryer

Once you have located the correct terminal for the motor operation (the terminal that sends voltage to the dryer motor), you will need to turn the timer to a dry cycle and press the push-to-start  on the dryer and check for 110 – 120v from the timer terminal for motor operation and the chassis ground (the unpainted frame of the dryer). If you have the voltage, the timer is most likely okay and the problem is elsewhere. If there is no voltage, the timer is defective and must be replaced.

5.  The capacitor.

The capacitor can be checked, but first you need to make sure the dryer is unplugged, and the capacitor is discharged.

To do this take a well insulated screwdriver and short it across the terminals of the capacitor.  Although today’s capacitors have a “bleed” resistor incorporated into their makeup, some times this resistor fails.  To protect yourself, go ahead and short across the capacitor terminals.  (Be careful.  If the capacitor still has a charge on it, it will spark and pop or snap when shorted.  Don’t jerk and hurt yourself.)

Now, with your meter set on a high ohms rating, take one probe and place it on one capacitor terminal.  While watching the meter, place the other probe on the other capacitor terminal.  If you do not get a reading, the capacitor is bad.  It will need to be replaced.

If you get a reading and it stays the same reading, the capacitor is shorted and needs replacing.  A good capacitor will send the meter up scale and then slowly allow the meter to go back down to the starting position.

If it does that, then the capacitor is good.

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