Furnaces use two primary methods of controlling fan operation. One method uses a set time, controlled by the furnace's main circuit board, to turn on the fan. The original method for automatic fan operation in a furnace is by using a temperature measuring device to activate the fan when a specified temperature is reached. A Camstat is a proven method of temperature-based furnace fan operation.
A Camstat has four wire terminals. Two sets of wire terminals operate a heater inside the Camstat. When the heater reaches a set temperature, a second set of wire terminals start the fan.
The furnace fan is wired between the second set of wire terminals on the Camstat. When the Camstat heater reaches the correct temperature, the wire terminals send a signal to start the fan operation.
A temperature setting determines the air temperature inside the furnace when the fan should turn off. Furnace manufacturers set the desired off temperature, but on-site technicians may have to adjust the off temperature, depending on the heating system and individual requirements.