How Dryer Motors Work
Most dryers in the United States are plugged into a 220 Volt A/C receptacle. However the motor on most dryers in the US, only uses 110 Volts A/C of that. So why do most dryers require 220 volts? Well it is because dryers need 220 volts to supply enough voltage and current flow to the heater to produce enough heat to dry clothes. By the way, most dryer motors outside the United States operate on 220 / 250 volts A/C. A complete explanation of motor fundamentals is beyond the scope of this forum of Appliance Repair Allen TX.
These windings have a different electrical resistance. Usually the start winding has a higher resistance than the run winding. The resistance in the winding delays the current flow in the motor windings. This delay allows the windings to create essentially four separate electromagnetic fields that help the motor to start. As soon as the motor starts to rotate the start windings need to be disengaged from the circuit. If not the motor will burn up because of the competing electromagnetic fields. This is a key function of the centrifugal switch on the motor. In addition to switching the heater on and off when the motor comes up to speed or shuts down, the centrifugal switch disengages a set of contacts that supply power to the start windings. The best way for non-technical people to check a dryer motor is to inspect it. When a dryer motor fails it usually burns up the windings inside the motor. Looking inside the motor you can see if the windings are burned. There is an odor associated with burned windings.