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.
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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.