A radiator cooling fan on a Chevy Cavalier is controlled by the computer. Its circuit goes from the battery positive to the fuse. From the fuse it travels to two relays: the low-speed and the high-speed relay. Both of these relays have a separate hot wire to the fan. They are actuated by the computer, which uses the engine coolant temperature (ECT) sensor to determine when to turn the fan on and which relay to actuate dependent on the temperature. The ECT sensor is a 2-wire thermistor. As engine coolant temperature increases, the thermistor resistance and signal voltage decreases. On a cold engine, the voltage is sent through a high resistance circuit in the computer. On a warm engine the voltage is sent through a low-resistance circuit in the computer. This dual circuit in the computer improves the accuracy of the ECT sensor over all temperature ranges.
Sunday, November 16th, 2014 AT 12:17 PM
