Component Description

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 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 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 PCM turns OFF the a/c clutch. When pressure drops below 206 kPa (30 psi), the PCM turns OFF the a/c clutch.

Fig.15 Evaporator Temperature Sensor:

Fig.16 Evaporator Temperature Sensor Setpoint:

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 Body Control Module (BCM) will send a Programmable Communications Interface (PCI) bus message to the Powertrain Control Module (PCM), which will check engine, coolant temperature, and refrigerant pressure temperature before turning ON the A/C Compressor Clutch. Turning ON the A/C Compressor Clutch will allow the system to cool the evaporator. The BCM will send a message to the PCM when the evaporator temperature becomes too cold. The PCM will then turn OFF the A/C Compressor Clutch, before evaporator freeze up occurs. The DRB III scan tool can be used to monitor this operation. The temperature setpoint at which the clutch is turned OFF varies with the outside ambient temperature. The temperature at which the clutch is turned ON is preset to 2 °F above the OFF setpoint mentioned above. Refer to Evaporator Temperature Sensor Setpoint table and for the correct setpoint.

Fig.18 Ambient Temp Sensor:

AMBIENT TEMP SENSOR
The ambient air temperature sensor is located on the inside of front bumper beam.

The ambient temperature sensor is used by the A/C system to adjust evaporator temperatures on vehicles equipped with the ATC system.

BLEND DOOR ACTUATOR
The blend door actuator is a motor/geartrain assembly which mechanically positions the blend door. The actuator is mounted to the bottom of the HVAC housing in the center.

A potentiometer in the actuator allows the BCM 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.

MODE DOOR ACTUATOR
The mode door actuator is a motor/geartrain assembly It mechanically positions the panel/bi-level door and the heat/defrost door. The actuator is mounted to the bottom of the HVAC housing on the left side.

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

RECIRCULATION DOOR ACTUATOR
The recirculation door actuator is a motor/ geartrain assembly. It mechanically positions the recirculation door. The actuator is mounted to the right side of the HVAC housing.

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

BLOWER MOTOR RESISTOR
The blower motor resistor is mounted to the lower right side of the heater-A/C housing in the passenger compartment, where it can be accessed for service.

The blower motor resistor has multiple resistor wires, each of which will change the resistance in the blower motor ground path to change the blower motor speed. The blower motor switch directs the ground path through the correct resistor wire to obtain the selected blower motor speed. The blower motor resistor cannot be repaired and, if faulty or damaged, it must be replaced.

With the blower motor switch in the lowest speed position the ground path for the motor is applied through all of the resistor wires. Each higher speed selected with the blower motor switch applies the blower motor ground path through fewer of the resistor wires, increasing the blower motor speed. When the switch is in the highest speed position, blower motor resistor is bypassed and the blower motor receives a direct path to ground.

THERMAL LIMITER SWITCH
The thermal limiter switch measures compressor surface temperature. If compressor surface temperature is excessive, the switch cuts battery feed to the compressor clutch coil. The switch will reset itself, once compressor surface temperature returns to normal. The switch is not adjustable or serviceable, if faulty the compressor must be replaced.

The thermal limiter switch interrupts battery feed to the compressor clutch coil when temperature reaches 122 - 128 °C (250 - 260 °F). The switch restores clutch coil battery feed when the temperature drops to 104 - 116 °C (220 - 240 °F).