The thermostat heater has no affect on the motor circuit. The purpose of the heater is to heat the thermostat when a low heat is selected. When a lower than max heat setting is used, the thermostat heater gets a higher voltage across it and produces heat. This basically makes the operating thermostat "think" that the dryer is hotter than it actually is and it will cycle the heat off earlier causing the overall temp of the dryer to be lower. The lower you set the heat setting, the higher the voltage across the thermostat heater and the hotter it gets causing the operating thermostat to cycle earlier still.
- Samurai Appliance Repair Man likes this