A/C Mode

The purpose of the Air Conditioning (A/C) system is to provide cool air and remove humidity from the interior of the vehicle. The A/C system is engaged when the heater and A/C control is in any mode. The A/C system can operate regardless of the temperature setting, as long as outside ambient temperature is above 4°C (40°F).

Power and ground are provided to the heater and A/C control by the fuse block on the battery positive voltage, ignition positive voltage and ground circuit.

When the A/C request is selected, a signal is sent from the heater and A/C control through the high and low pressure switches to the Engine Control Module (ECM). Both pressure switches must be closed for the request signal to complete it's path to the ECM.

The ECM turns on the A/C compressor by providing a path to ground through the A/C compressor relay control circuit for the A/C compressor relay. Power is provided to the A/C compressor relay coil through the ignition voltage circuit from the fuse block. Once the relay closes its internal switch, power from the battery is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. Ground to the A/C compressor is supplied from the secondary cooling fan temperature switch. The secondary cooling fan temperature switch is closed until the temperature exceeds 120°C (248°F). When the secondary cooling fan temperature switch is open a path for ground will not present at the A/C compressor clutch. The secondary cooling fan temperature switch is grounded through the ground circuit. When A/C is requested the water cut off vacuum solenoid valve is engaged through the vacuum solenoid valve control circuit. When the water cut off vacuum solenoid valve is engaged, vacuum is supplied to the water cut off valve and coolant flow is bypasses the heater core. The A/C compressor diode prevents a voltage spike from entering the vehicles electrical system. The A/C clutch relay control circuit is grounded internally within the ECM. When the ECM reads wide open throttle, the ECM will shut off the compressor for 20 seconds.