The radiator fan relay is used to turn on the radiator fan. For 1984 models, the relay is turned on by a temperature switch on the radiator and by the logic module. The temperature switch turns the fan on at 210^F and off at 180^F. The logic module turns the relay on when the A/C compressor clutch is engaged. For 1985 and later models, the relay has two, separate inputs. The main input is from the logic module, which turns the fan on and off at different temperatures, based on the vehicle speed. It will turn the fan on at 220^F and off at 210^F if the speed is below 35 mph, or on at 240^F and off at 230^F if the speed is above 45 mph. The area in between these thresholds is an overlap zone where the fan may be on or off. The second input is from the A/C Cutout (WOT) Relay, which will turn the radiator fan on if the A/C compressor is being turned on.
For 1984 models, if the coolant temperature is below 150^F, the logic module monitors the relay input. If the relay is off when the clutch is on or on when the clutch is off, a fault code 35 is stored. For 1985 and later models, when the logic module is turning on or off the relay, it momentarily checks the output of the relay driver to see if it is responding the way it should. If it does not see about 0V when on (open circuit) or 12V when off (short circuit), a fault code 35 is stored.
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Updated 12/19/2003.
Copyright © 1996-2003 Russ W. Knize.