Cooling System: Description and Operation
How the Circuit WorksPower Supply
Closing the PGM-FI main relay 1 supplies battery voltage to the radiator fan relay coil through fuse 7 (in the under-hood fuse/relay box). Fuse 16 (in the under-hood fuse/relay box) provides battery voltage at all times to the radiator fan relay contacts.
With the ignition switch in ON (II), fuse 30 (in the under-dash fuse/relay box) supplies battery voltage to the fan control relay coil and the A/C condenser fan relay coil. Fuse 15 (in the under-hood fuse/relay box) provides battery voltage at all times to the A/C condenser fan relay contacts.
The climate control unit communicates A/C request information to the PCM through the B-CAN and F-CAN multiplex communication networks.
A/C ON
When the PCM receives the "A/C ON" information, it grounds the A/C condenser fan relay coil. Energizing the A/C condenser fan relay turns on the A/C condenser fan motor, which grounds through the deactivated fan control relay through the radiator fan motor, causing both fans to run at reduced speed. The fans run whenever the A/C compressor is activated.
If the refrigerant line pressure rises above 1470 kPa (213 psi), the A/C pressure sensor signals the climate control unit, which signals the PCM to ground the radiator fan relay coil and the fan control relay coil. Energizing the radiator fan relay provides battery voltage directly to the radiator fan motor. Energizing the fan control relay provides a direct path to ground for the A/C condenser fan motor. This causes the radiator fan motor and the A/C condenser fan motor to run at full speed.
High Coolant Temperatures
In high coolant temperature conditions (above 207 °F (97 °C)) the PCM grounds the radiator fan relay coil and the fan control relay coil. Energizing the radiator fan relay provides battery voltage directly to the radiator fan motor. Energizing the fan control relay provides a direct path to ground for the A/C condenser fan motor. This causes the radiator fan motor and the A/C condenser fan motor to run at full speed.
If the refrigerant line pressure drops below 193 kPa (28 psi), the A/C pressure sensor signals the climate control unit to turn off the A/C compressor. The PCM removes the ground from the radiator fan relay coil, the fan control relay coil, and the A/C condenser fan relay coil, turning off both fan motors.
Refrigerant at High Pressure
If the refrigerant line pressure exceeds 3140 kPa (455 psi), the A/C pressure sensor signals the PCM to turn off the A/C compressor. The PCM removes the ground from the radiator fan relay coil, the fan control relay coil, and the A/C condenser fan relay coil, turning off both fan motors.