DriveMaster® - Lesson 2: Control Components, © 2001 Horton, Inc.

	LESSON 2: CONTROL COMPONENTS
Vehicles not using an ECM usually have two sensors to automatically turn the fan on and off. First is the engine coolant thermal switch and, second, the air conditioning refrigerant pressure switch.
	2.1 Engine Coolant Thermal Switch	INDEX
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	The engine coolant thermal switch is mounted in the water jacket on the engine. Thermal switches are either normally-open or normally-closed depending upon the electrical control system. • In a normally-open thermal switch, the electrical contacts are open when the temperature is below the set point and closed when the temperature is above the set point. • In a normally-closed thermal switch, the electrical contacts are closed when the temperature is below the set point and open when the temperature is above the set point.	Learning Objectives: • Describe the function of a thermal switch in the fan drive control system. • State the difference between normally-open and normally-closed components.
		NOTE: Thermal switch reset point is usually 7^o F [3.9^o C] below the set point. Truck designers will typically specify a thermal switch with a set point 10-15^o F [5.6-8.3^o C] higher than the fully open temperature of the engine thermostat.
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