Part 1 of 4

A/C COMPRESSOR CLUTCH
The compressor clutch components provide a way to drive the compressor. The compressor clutch assembly consists of a stationary electromagnetic coil, hub bearing and pulley assembly and a clutch plate. The compressor clutch and coil assembly are the only serviced parts on the compressor.

When clutch engages the compressor is then driven by the engine serpentine drive belt. The clutch engagement is controlled the heater-A/C mode control switch, a/c pressure transducer, evaporator probe, thermal limiter switch, compressor clutch relay and Powertrain Control Module (PCM).

A/C COMPRESSOR CLUTCH COIL
The compressor clutch coil is an electromagnetic and provides a way to engage the compressor clutch plate. The electromagnetic coil unit, hub bearing and pulley assembly are retained on the compressor front housing with snap rings. The compressor clutch and coil assembly are the only serviced parts on the compressor.

The coil is controlled by the heater-A/C mode control switch, a/c pressure transducer, evaporator probe, thermal limiter switch, compressor clutch relay and Powertrain Control Module (PCM). When the clutch coil is energized, it magnetically draws the clutch plate into contact with the pulley. When the coil is not energized the pulley freewheels on the clutch hub bearing, which is part of the pulley.

A/C COMPRESSOR CLUTCH RELAY
The compressor clutch relay is a International Standards Organization (ISO) micro-relay. The terminal designations and functions are the same as a conventional ISO relay. However, the micro-relay terminal orientation (footprint) is different, the current capacity is lower, and the relay case dimensions are smaller than those of the conventional ISO relay.

The compressor clutch relay is located in the Power Distribution Center (PDC) in the engine compartment. Refer to the PDC label for relay identification and location.

The A/C compressor clutch relay is a electromechanical device that switches battery current to the A/C compressor clutch coil when the Powertrain Control Module (PCM) grounds the coil side of the relay. The PCM responds to inputs from the A/C heater control (Manual Temperature Control, or Automatic Temperature Control) , the Body Control Module (BCM), and the a/c pressure transducer.

The compressor clutch relay cannot be repaired and, if faulty or damaged, it must be replaced.

A/C PRESSURE TRANSDUCER
The A/C pressure transducer is located on the discharge line near the condenser and functions as a refrigerant system pressure sensor. This switch prevents compressor operation when the discharge line pressure approaches extreme levels. The transducer is a factory-calibrated unit and cannot be adjusted or repaired. If faulty or damaged, it must be replaced.

When discharge line pressure rises above 2971 kPa (431 psi) the switch contacts open and interrupt the A/C clutch relay signal from the PCM. The switch contacts also open when pressure drops below 206 kPa (30 psi).

Fig.15 Evaporator Temperature Sensor:

EVAPORATOR TEMPERATURE SENSOR
The evaporator temperature sensor is located at the coldest point on the face of the evaporator. The switch is attached to the evaporator coil with the sensing probe inserted into the coil fins. The evaporator temperature sensor prevents condensate water on the evaporator coil from freezing and obstructing A/C system air flow.

The sensor is used to switch the clutch OFF before evaporator freeze-up occurs. Output from the probe is sampled by the Body Control Module. The clutch is switched OFF when the sensor temperature reaches 1.1 °C (34 °F). The clutch is switched back ON when the sensor temperature reaches 2.2 °C (36 °F).

Fig.19 ATC Sun Sensor:

SUN SENSOR
The sun sensor is only used on vehicles equipped with Automatic Temperature Control (ATC). The sensor is mounted on the top of the instrument panel below the instrument panel top cover.

The sun sensor is not a thermistor type sensor but rather a photo diode. For this reason the sun sensor responds to sun light intensity rather than temperature. It is used to aid in determining proper mode door position, temperature door position and blower speed. The sun sensor is also used to sense day/night conditions for automatic headlight control if so equipped, and has an LED indicator for the vehicle security system.

The sun sensor is not serviceable and must be replaced if found to be defective.

Fig.21 Ambient Temp Sensor:

AMBIENT TEMP SENSOR
The ambient air temperature sensor is located on the inside of front bumper beam. This sensor informs the ATC system of the ambient temperature outside vehicle.

The ambient temp sensor is used by the ATC system to adjust blower speed, temperature offsets, evaporator temperatures and mode control.

BLEND DOOR ACTUATOR
The blend door actuator is an electric motor which mechanically positions the blend door. The actuator is mounted to the the bottom of the HVAC housing in the center.

A potentiometer in the actuator allows the BCM (for both manual and ATC systems) to know the exact position of the blend door at all times. The blend door actuator is not serviceable and must be replaced if found to be defective.