If the dryer does not start, you need to make a few observations in order to work toward a diagnosis. If the motor is humming or trying to turn but does not engage, check the following:
Make sure a garment or excess lint build up isn't stuck in the blower wheel, causing the motor to be physically unable to turn. If the blower wheel turns independently of the motor, or it is stripped on the motor shaft, you should replace the blower wheel. Inspect the drum support system, including the rear bearing, rollers, front glides or belt tension wheel for excessive wear, which could make the drum hard to turn. If the drum turns freely, and you have no obstructions causing any drag on the motor, replace the motor. The motor humming is usually an indication the motor is receiving proper power, but it is just unable to start on its own.
If the dryer is "dead" or you hear nothing when you push start on the unit, there are several electrical components to check. First, check the wall socket to make sure you have proper voltage to the dryer. An electric dryer should have 240 volts or two "legs" of 120 volts of power at the terminal block on the dryer. A gas dryer should have 120 volts of power at the receptacle in which it is plugged into. Once you've verified proper power to the unit, proceed with diagnosing the internal components of the dryer. Use the wiring diagram on the unit itself with an electrical test meter to take the guess work out of the diagnosis.
Check the door switch. On the frame of the dryer where the door closes, there is a door switch that should “click” when actuated. This doesn't absolutely mean the switch is good, but if it doesn't “click” it's probably bad. You can test the switch for continuity with a volt/ohm meter.
Check the push button start switch to make sure the contacts are closing properly when the switch is depressed. You can do this with an ohm meter with the wires removed from the switch. If this function is done through the timer, you can check the timer contacts used for this purpose in the same manner. If the motor only runs when the start switch is pushed the motor may be plugged with lint or it may have a bad winding. When a motor has a bad winding it will not stay running once the start switch (or timer) is released.
Most dryers built in the last 10 years have one or more thermostat-like parts that will shut down operation if the dryer overheats. These "one time" thermal fuses are located on the heater housing or on the blower housing inside the unit and must be replaced once they have been tripped. More importantly, you need to determine why the unit has overheated before you resume operating the dryer. Check the venting to make sure it's clean all the way to the outdoors and that it's as short as possible. Also, use a thermometer to check the outlet temperature of the dryer. If it is overheating, replace the control thermostat used for that cycle. A heating element that is touching the frame or cabinet can provide constant heat, even when the control thermostat has cycled off. So be sure to inspect the element for any grounds or shorts.
When all the components listed above seem to be in working order, you either have open contacts in the timer not supplying power to the motor, or the motor itself has an open winding. On occasion, you may have a burnt or broken wire causing the failure. Inspect the wiring around the motor area.
TheRepairGuru --- www.repairclinic.comhttp://www.repairclinic.com/Dryer-Parts