Cooling System: Description and Operation

How the Circuit Works (L4)

Power Supply

Battery voltage is supplied at all times through Multi-fuse 3 (in the under-hood fuse/relay box) to the contacts of the Radiator Fan Relay and through fuse 5 (in the under-hood fuse/relay box) to the contacts of the A/C Condenser Fan Relay. With the ignition switch in ON (II), battery voltage is supplied through fuse 16 (in the driver's under-dash fuse/relay box) to the coil of the Radiator Fan Relay With the engine running, battery voltage is supplied through fuse 21 (in the under-hood fuse/relay box) to the A/C Condenser Fan Relay coil.

Elevated Coolant Temperatures

In elevated coolant temperature conditions, the ECM/PCM provides ground to the coils of the A/C Condenser Fan Relay and the Radiator Fan Relay, energizing them. Battery voltage is supplied to the A/C Condenser Fan Motor and Radiator Fan Motor through their respective energized relays, which activates the motors.

A/C ON

The Driver's MICU detects that the A/C is ON from an input through the A/C Pressure Switch to the HVAC Control Unit or Climate Control Unit. The Driver's MICU communicates this information to the ECM/PCM through the B-CAN and F-CAN networks of the Multiplex Integrated Control System. Upon receiving the A/C ON information, the ECM/PCM provides ground to the coils of the A/C Condenser Fan Relay and the Radiator Fan Relay, energizing them. Battery voltage is supplied to the A/C Condenser Fan Motor and Radiator Fan Motor through their respective energized relays, which activates the motors.

Refrigerant at Low Pressure

If the refrigerant pressure drops below 196 kPa (28 psi), the A/C Pressure Switch opens, removing the A/C ON input from the Driver's MICU. The Driver's MICU detects that the A/C Pressure Switch is open and the A/C should be turned OFF The Driver's MICU communicates this information to the ECM/PCM through the B-CAN and F-CAN networks of the Multiplex Integrated Control System. Upon receiving the A/C OFF information, the ECM/PCM removes ground from the coils of the A/C Condenser Fan Relay and the Radiator Fan Relay, deenergizing them. This removes battery voltage from the A/C Condenser Fan Motor and Radiator Fan Motor, which deactivates the motors.

Refrigerant at High Pressure

If the refrigerant pressure rises above 3140 kPa (455 psi), the A/C Pressure Switch opens, removing the A/C ON input from the Driver's MICU. The Driver's MICU detects that the A/C Pressure Switch is open and the A/C should be turned OFF The Driver's MICU communicates this information to the ECM/PCM through the B-CAN and F-CAN networks of the Multiplex Integrated Control System. Upon receiving the A/C OFF information, the ECM/PCM removes ground from the coils of the A/C Condenser Fan Relay and the Radiator Fan Relay, deenergizing them. This removes battery voltage from the A/C Condenser Fan Motor and Radiator Fan Motor, which deactivates the motors.