HowStuffWorks published a cross-section of the common hair dryer, showing the schematics beneath its plastic housing. The power cord connects directly to the on/off, speed and heat switches on the handle, which control the motor and fan in the body of the dryer and the heating elements in the nozzle.
The mechanisms that allow a hair dryer to work are fairly simple. When the power cord is plugged in and the power switch is turned on, the electric current from the outlet starts the motor. The motor turns the fan at varying speeds, according to the speed switch, and the fan pushes air into the nozzle of the dryer.
Many dryers are equipped with a heat switch that lets the user determine the temperature of the air coming out of the dryer. When the dryer is set to blow cool or cold air, the heating elements don't heat up, and the air passes through the nozzle at room temperature. When the dryer is set to blow hot air, the heating elements turn on, and as the air flows from the fan and through the heated coils, the air becomes hot. When the hot air passes out of the grated nozzle and onto the hair, it speeds up the drying process by evaporating excess water from the surface of the hair.