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Fig.4 Compressor Clutch - Typical:

A/C COMPRESSOR CLUTCH
The compressor clutch assembly consists of a stationary electromagnetic coil, a hub bearing and pulley assembly, and a clutch plate. The electromagnetic coil unit and the hub bearing and pulley assembly are each retained on the nose of the compressor front housing with snap rings. The clutch plate is keyed to the compressor shaft and secured with a bolt.

The compressor clutch components provide the means to engage and disengage the compressor from the engine serpentine accessory drive belt. When the clutch coil is energized, it magnetically draws the clutch into contact with the pulley and drives the compressor shaft. When the coil is not energized, the pulley freewheels on the clutch hub bearing, which is part of the pulley. The compressor clutch and coil are the only serviced parts on the compressor.

The compressor clutch engagement is controlled by several components: the a/c switch on the a/c heater control panel, the Automatic Zone Control (AZC) control module (if the vehicle is so equipped), the evaporator probe, the a/c high pressure transducer, the a/c compressor clutch relay the body control module (BCM) and the Powertrain Control Module (PCM). The PCM may delay compressor clutch engagement for up to 30 seconds. Refer to Electronic Control Modules for more information on the PCM controls.

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 a electromechanical device that switches battery current to the 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 compressor switch on the a/c heater control panel, the Automatic Zone Control (AZC) control module (if the vehicle is so equipped), the a/c fin probe, and the a/c high pressure transducer.

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

A/C HEATER CONTROL
The manual temperature control HVAC system uses a combination of electrical, and vacuum controls. The Automatic Zone Control (AZC) HVAC system uses only electrical controls. These controls provide the vehicle operator with a number of setting options to help control the climate and comfort within the vehicle. Refer to the owner's manual in the vehicle glove box for more information on the suggested operation and use of these controls.

Fig.12 A/C Heater Control Panels:

Both a/c heater control panels are located on the instrument panel inboard of the steering column and below the radio. Both control panels contain rotary-type temperature control knob(s), a rotary-type mode control switch knob, a rotary-type blower motor speed switch knob and an air conditioning compressor push button switch. The rear window defogger push button switch is also located on a/c heater control panel. The AZC control panel also features a recirculation push button switch and a vacuum fluorescent display area.

The AZC control module uses infrared sensing technology to control occupant comfort levels, not the actual passenger compartment air temperature. Dual infrared sensors mounted in the face of the control unit independently measure the surface temperature to maintain customer-perceived comfort temperature under changing conditions. Dual Zone temperature control provides wide side-to-side variation in comfort temperature to exceed the needs of either front seat occupant. This sensing system replaces interior air temperature and solar sensors used to approximate direct sensing control through complex control programs.

Both the manual A/C Heater control panel and the AZC control panel are serviced only as complete units and cannot be repaired. If faulty or damaged, the entire control panel unit must be replaced.

A/C PRESSURE TRANSDUCER
The A/C pressure transducer is installed on a fitting located on the refrigerant discharge line near the condenser. An internally threaded hex fitting on the transducer connects it to the externally threaded Schrader-type fitting on the discharge line. A rubber O-ring seals the connection between the transducer and the discharge line fitting. Three terminals within a molded plastic connector receptacle on the top of the transducer connect it to the vehicle electrical system through a take out and connector of the headlamp and dash wire harness.

The A/C pressure transducer cannot be adjusted or repaired and if faulty or damaged, it must be replaced.

The A/C pressure transducer monitors the pressures in the high side of the refrigerant system through its connection to a fitting on the discharge line. The transducer will change its internal resistance in response to the pressures it monitors. The Powertrain Control Module (PCM) provides a five volt reference signal and a sensor ground to the transducer, then monitors the output voltage of the transducer on a sensor return circuit to determine refrigerant pressure. The PCM is preprogrammed to respond to this and other sensor inputs by controlling the operation of the air conditioning compressor clutch and the radiator cooling fan to help optimize air conditioning system performance and to protect the system components from damage. The A/C pressure transducer input to the PCM will also prevent the air conditioning compressor clutch from engaging when the ambient temperatures are below about 0.556 °C (33 °F) due to the pressure/temperature relationship of the refrigerant. The Schrader-type valve in the liquid line fitting permits the A/C pressure transducer to be removed or installed without disturbing the refrigerant in the system. The A/C pressure transducer is diagnosed using the DRB III scan tool. Refer to the appropriate diagnostic information.

BLOWER MOTOR CONTROLLER
Models equipped with the optional Automatic Zone Control (AZC) system have a blower motor controller. The controller allows the selection of almost infinitely variable blower motor speeds. The controller is mounted to the HVAC housing, under the instrument panel and just inboard of the blower motor, in the same location used for the blower motor resistor on manual temperature control systems. It can be accessed without removing any other components.

The blower motor controller output to the blower motor can be adjusted by the blower motor speed switch knob on the AZC A/C Heater control panel, or it can be adjusted automatically by the logic circuitry and programming of the AZC control module. In either case, the AZC control module sends the correct pulse width modulated signal to the blower motor controller to obtain the selected or programmed blower motor speed.

The blower motor controller cannot be repaired and, if faulty or damaged, it must be replaced.

BLOWER MOTOR RESISTOR BLOCK
Models with the standard manual temperature control system have a blower motor resistor. The blower motor resistor is mounted to the bottom of the HVAC housing, under the instrument panel and just inboard of the blower motor. It can be accessed for service without removing any other components.

The resistor has multiple resistor wires, each of which will reduce the current flow to the blower motor to change the blower motor speed by changing the resistance in the blower motor ground path. The blower motor switch directs the ground path through the correct resistor wire to obtain the selected speed.

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 blower motor switch is in the highest speed position, the blower motor resistor is bypassed and the blower motor receives a direct path to ground.

The blower motor resistor cannot be repaired and, if faulty or damaged, it must be replaced.