A/C: Fans and Compressor Control

The air conditioning system controls the radiator fan, the condenser fan, and the AIC compressor clutch.

Radiator Fan (USA)

Voltage is provided at all times to the radiator fan motor and the radiator fan control module. Voltage is provided in RUN and START to the radiator fan control module. The radiator fan control module provides power to the radiator fan relay when the ignition switch is in RUN or START; and for 15 minutes after the ignition is switched off. The radiator fan relay is energized whenever the YEL/GRN wire is grounded. The YEL/GRN wire can be grounded either by the engine coolant temperature (ECT) switch or by the AIC switch and fan switch.


Radiator Fan (Canada)

When the ignition switch is in RUN, voltage is applied to the radiator fan motor and the radiator fan relay. Whenever a YEL/GRN wire is grounded, the radiator fan relay energizes and the radiator fan motor will run. The YEL/GRN wires can be grounded by the engine coolant temperature (ECT) switch, or the AIC switch and fan switch.


Condenser Fan (USA)

The radiator fan control module provides power to the condenser fan relay coil, with the ignition switch in RUN and START; and for 15 minutes after the ignition is switched off. The condenser fan runs under the same condition as the radiator fan except that the fan timer can ground the coil when the engine oil temperature switch is closed. The condenser fan can run after the ignition is switched off, until the engine oil temperature switch opens or the control module removes power.


Condenser Fan (Canada)

Voltage is applied to the condenserfan motor when the condenser fan relay is energized. The condenser fan relay coil receives voltage when the ignition switch is in RUN, and is grounded by the same components that can ground the radiator fan.


A/C Compressor Clutch

When the AIC switch is turned on and the fan switch is in position 1,2,3 or 4, the RED/BLU wire input to the engine control module (ECM) is grounded. This signals the ECM to ground the AIC compressor clutch relay by grounding the YEL wire output. The relay is energized, voltage is applied to the AIC compressor clutch, and the clutch engages. If the A/C pressure switch or A/C thermostat is open, the A/C switch cannot ground the engine control module (ECM) input and the A/C compressor clutch will not engage.


A/C Pressure Switch

AIC system pressure below 215 kPa (33 psi) psi indicates a loss of refrigerant. The pressure switch will open with system pressure below 28 psi to prevent compressor damage.


AIC Thermostat

The AIC thermostat senses evaporator temperature. With evaporator temperature above 41°F, the switch is closed. With evaporator temperature below 33°F, the switch opens. In this way, the evaporator temperature stays above 32°F and moisture on the evaporator fins does not freeze and block air flow.


A/C Diodes

These diodes prevent the engine coolant temperature (ECT) switch from grounding the "A/C on" input to the engine control module (ECM).