Cooling System: Description and Operation

Cooling fan operation is controlled by the fan timer module, which monitors signals from a thermo sensor, underhood temperature sensor and the A/C compressor clutch. The timer operates the cooling fan by controlling voltage applied to the fan relay control coil. Battery voltage is applied directly from the main fuse to the relay switch circuit and timer bypass circuit, and voltage is applied to the timer main circuits through the ignition switch start and run contacts. The timer module controls voltage applied to the relay control coil circuit, and the control coil circuit is completed to ground either through the thermo sensor or timing module. When current flows through the relay coil circuit, the relay contacts close and voltage is applied to the cooling fan motor.

During normal operation, voltage is applied to the relay coil by the timer module and fan operation is controlled by the thermo sensor. When coolant temperature is approximately 190°F, current flows through the relay coil circuit and voltage is applied to the fan motor. When coolant temperature is below 190°F, the thermo sensor contacts are open and the cooling fan does not operate. However, when the A/C is turned on, the timer energizes the relay coil and the cooling fan operates as long as the clutch remains energized.

When the engine is turned off, the timer module remains energized and monitors signals from the underhood temperature sensor. If underhood temperature exceeds 220°F, the timer activates the fan relay and the cooling fan is energized. The cooling fan will operate for a maximum of 15 minutes after the engine has stopped or until underhood temperature drops below 220°F.