A dryer is simply a large drum into which wet laundry is loaded. A motor with pulleys -- connected by a series of belts -- turns the drum. Air heated by a gas heater or electric heating element is blown through the drum to dry the laundry. The temperature and speed of the drum are controlled by a series of thermostats operated from a timer device on the control panel of the dryer.
As a safety device, a dryer usually has a door switch that activates the working parts. Unless the door is properly closed, the dryer won't work, regardless of the settings on the control panel. Many dryers are equipped with a reset button on the control panel. If the motor won't run, let the dryer cool for about ten minutes. Then push the reset button. If there are no problems with the motor, switches, or electrical system, this should restart the dryer. Caution: Before doing any work on the dryer, make sure it's unplugged. Disconnect the grounding wire. If it is a gas-fueled dryer, close the gas-supply valve to shut off the unit's gas supply.