Check all your fuses first. This is a 2 speed system and may have lost low speed. When you test the motor, make sure you test both speeds.
A two speed coolant fan is turned on and off by the low and high speed coolant fan relays.
For low speed operation, the low speed coolant fan relay coil is grounded through the ECM or the low speed contacts of the A/C dual pressure switch. The ECM grounds the coil when vehicle speed is less than 35 mph and the engine coolant is warmed up. The A/C dual pressure switch low speed contacts close with high refrigerant pressure above 260 psi.
With the low speed relay coil grounded, its contacts close. Voltage is applied through the coolant fan resistor to the coolant fan. The resistor reduces battery voltage supplied to the fan so that the fan runs at a low speed.
For high speed operation, the high speed coolant fan relay coil is grounded through the high speed contacts in the A/C dual pressure switch or by the temperature switch. The pressure switch high speed contacts close at a refrigerant pressure above 300 psi. The temperature switch closes when coolant temperature rises above 230 °F.
With the high speed relay coil grounded, its contacts close. Battery voltage is applied to the coolant fan. The fan runs at high speed.
The heavy duty coolant fan is turned on and off by the heavy duty coolant fan relay. The heavy duty coolant fan relay is grounded through the high speed contacts in the A/C dual pressure switch or by the temperature switch. With the heavy duty relay coil grounded, its contacts close. Battery voltage is applied to the heavy duty coolant fan. The fan runs at high speed.
Thursday, September 30th, 2010 AT 7:25 PM
