Cooling System: Description and Operation

Fans

How the Circuit Works

Battery voltage is supplied at all times through fuses 20 and 19 (in the under-hood fuse/relay box) to the contacts of the A/C condenser fan relay and radiator fan relay respectively. With the ignition switch in ON (II), battery voltage is supplied through fuse 30 (in the under-dash fuse/relay box) to the A/C condenser fan relay. With the engine running, battery voltage is supplied through fuse 23 (in the under-dash fuse/relay box) to the radiator fan relay coil.

Extremely High Coolant Temperatures

In extremely high coolant temperature conditions (Above 206 °F (97 °C) ), the PCM provides ground to the coils of the A/C condenser fan relay, the radiator fan relay, and the fan control 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 at high speed.

A/C ON

The relay control module detects that the A/C is ON when the HVAC control unit (RT, RTX, LX) or climate control unit (RTS, RTL, EX-L) grounds the reference voltage sent through the A/C pressure switch. The relay control module communicates this information to the PCM through the B-CAN and F-CAN networks of the multiplex system. Upon receiving the A/C ON information, the PCM provides ground to the coil of the A/C condenser fan relay, energizing it. Battery voltage is supplied to the A/C condenser fan motor and radiator fan motor in series through the energized relay, which activates the motors at low speed.

If the refrigerant pressure rises above 1,520 kPa (221 psi), the A/C pressure switch closes, which signals the PCM to run the fans at high speed. The PCM provides ground to the coils of the A/C condenser fan relay, the radiator fan relay, and the fan control 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 at high speed.

Refrigerant at Low Pressure

If the refrigerant pressure drops below 196 kPa (28 psi), the A/C pressure switch opens, removing ground from the reference voltage. The relay control module detects that the A/C pressure switch is open, and the A/C needs to be turned OFF The relay control module communicates this information to the PCM through the B-CAN and F-CAN networks of the multiplex system. Upon receiving the A/C OFF information, the PCM removes ground from the coil of the A/C condenser fan relay, deenergizing it. 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 3,140 kPa (455 psi), the A/C pressure switch opens, removing ground from the reference voltage. The relay control module detects that the A/C pressure switch is open, and the A/C needs to be turned OFF The relay control module communicates this information to the PCM through the B-CAN and F-CAN networks of the multiplex system. Upon receiving the A/C OFF information, the PCM removes ground from the coils of the A/C condenser fan relay, the radiator fan relay, and the fan control relay, deenergizing them. This removes battery voltage from the A/C condenser fan motor and radiator fan motor, which deactivates the motors.