Part 1A

Fig.2 A/C Pressure Transducer:

A/C PRESSURE TRANSDUCER
The A/C pressure transducer is a switch that is installed on a fitting located on the refrigerant liquid line between the filter-drier and the expansion valve in the right rear corner of the engine compartment. An internally threaded hex fitting on the transducer connects it to the externally threaded Schrader-type fitting on the liquid line. A rubber O-ring seals the connection between the transducer and the liquid 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 musty 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 liquid line. The transducer will change its internal resistance in response to the pressures it monitors. The Powertrain Control Module (PCM) provides a 5 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 programmed 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 ambient temperatures are below about 10 °C (50 °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 a DRB III scan tool. Refer to the appropriate diagnostic information.

FRONT BLEND DOOR ACTUATOR
The blend door actuators are reversible, 12-volt Direct Current (DC), servo motors. Models with the single zone heater and air conditioner system have a single blend air door, which is controlled by a single blend door actuator. Models with the optional dual zone front heater and air conditioner system have dual blend air doors, which are controlled by two blend door actuators. The single zone blend door actuator is located on the driver side end of the heater-A/C housing unit, close to the dash panel. In the dual zone system, the same blend door actuator used for the single zone system becomes the passenger blend door actuator, and is mechanically connected to only the passenger side blend air door. In the dual zone system, a second separate blend door actuator is also located on the driver side end of the heater-A/C housing unit close to the instrument panel, and is mechanically connected to only the driver side blend air door.

The blend door actuators are interchangeable with each other, as well as with the actuators for the mode door and the recirculation air door. Each actuator is contained within an identical black molded plastic housing with an integral wire connector receptacle. Two integral mounting tabs allow the actuator to be secured with two screws to the heater- A/C unit housing. Each actuator also has an identical output shaft with splines that connects it to the linkage that drives the proper blend air door. The blend door actuators do not require mechanical indexing to the blend door linkage, as they are electronically calibrated by the heater-A/C control module. The blend door actuators cannot be adjusted or repaired and, if damaged or faulty they must be replaced.

Each blend door actuator is connected to the heater-A/C control module through the vehicle electrical system by a dedicated two-wire take out and connector of the HVAC wire harness. The blend door actuator can move the blend air door in two directions. When the heater-A/C control module pulls the voltage on one side of the motor connection high and the other connection low, the blend air door will move in one direction. When the module reverses the polarity of the voltage to the motor, the blend air door moves in the opposite direction. When the module makes the voltage to both connections high or both connections low, the blend air door stops and will not move. These same motor connections also provide a feedback signal to the heater-A/C control module. This feedback signal allows the module to monitor the operation and relative positions of the blend door actuator and the blend air door. The heater-A/C control module learns the blend air door stop positions during the calibration procedure and will store a Diagnostic Trouble Code (DTC) for any problems it detects in the blend door actuator circuits. The blend door actuator can be diagnosed using a DRB III scan tool. Refer to the appropriate diagnostic information.

Fig.6 Blower Motor Relay:

FRONT BLOWER MOTOR RELAY
The blower motor relay is a International Standards Organization (ISO) mini-relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The ISO mini-relay terminal functions are the same as a conventional ISO relay However, the ISO mini-relay terminal pattern (or footprint) is different, the current capacity is lower, and the physical dimensions are smaller than those of the conventional ISO relay. The blower motor relay is located in the Intelligent Power Module (IPM), which is in the engine compartment near the battery. See the fuse and relay layout map molded into the inner surface of the IPM cover for blower motor relay identification and location.

The black, molded plastic case is the most visible component of the blower motor relay Five male spade-type terminals extend from the bottom of the base to connect the relay to the vehicle electrical system, and the ISO designation for each terminal is molded into the base adjacent to each terminal.

The blower motor relay is an electromechanical switch that uses a low current input from the Front Control Module (FCM) to control the high current output to the blower motor resistor (manual heater-A/C control) or blower power module (ATC control). The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. The resistor or diode is connected in parallel with the relay coil in the relay, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The blower motor relay terminals are connected to the vehicle electrical system through a receptacle in the Intelligent Power Module (IPM). The inputs and outputs of the blower motor relay include:
- The common feed terminal (30) receives a battery current input from the battery through a B(+) circuit at all times.
- The coil ground terminal (85) receives a ground input through the front/rear blower motor relay control circuit only when the FCM electronically pulls the control circuit to ground.
- The coil battery terminal (86) receives a battery current input from the battery through a B(+) circuit at all times.
- The normally open terminal (87) provides a battery current output to the blower motor resistor (manual heater-A/C control) or blower power module (automatic heater-A/C control) through a fuse in the IPM on the fused front blower motor relay output circuit only when the blower motor relay coil is energized.
- The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the blower motor relay coil is de-energized.

Refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, further details on wire harness routing and retention, as well as pin-out and location views for the various wire harness connectors, splices, and grounds.

Fig.9 Blower Motor Resistor:

BLOWER MOTOR RESISTOR
A blower motor resistor is used on this model when it is equipped with the manual heater-A/C control. Models equipped with the optional Automatic Temperature Control (ATC) use a blower power module, instead of the blower motor resistor. The blower motor resistor is installed in a mounting hole in the heater/AC housing, directly behind the glove box opening of the instrument panel. The resistor consists of a molded plastic mounting plate with two integral connector receptacles. Concealed behind the mounting plate within the heater/AC housing are four coiled resistor wires contained within a protective stamped steel cage. The resistor mounting plate is secured with two screws to the heater/AC housing and is accessed for service by rolling down the glove box from the instrument panel.

The blower motor resistor wires will get hot when in use. Do not touch the resistor wires or the protective cage if the blower motor has been running. The blower motor resistor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The blower motor resistor is connected to the vehicle electrical system through a dedicated take out and connector of the instrument panel wire harness. A second connector receptacle receives the pigtail wire connector from the blower motor. The blower motor resistor has multiple resistor wires, each of which will reduce the current flow through the blower motor to change the blower motor speed. The blower motor switch in the manual heater-A/C control directs the ground path for the blower motor 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 wires are bypassed and the blower motor receives a direct path to ground through the blower motor switch. The blower motor resistor may be diagnosed using conventional diagnostic tools and methods.

Fig.11 Compressor Clutch - Typical:

COMPRESSOR CLUTCH
The compressor clutch assembly consists of a stationary electromagnetic coil with a zener diode, 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 or splined to the compressor shaft, and secured with a bolt.

The compressor clutch plate and pulley unit, or the clutch coil are available for separate service replacement. The clutch coil zener diode is integral to the clutch coil pigtail wire and connector and, if faulty or damaged, the clutch electromagnetic coil unit must be replaced.

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 plate into contact with the clutch 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.

A zener diode is connected in parallel with the clutch electromagnetic coil. This diode controls the dissipation of voltage induced into the coil windings by the collapsing of the electromagnetic fields that occurs when the compressor clutch is disengaged. The zener diode dissipates this induced voltage by regulating a current path to ground. This arrangement serves to protect other circuits and components from potentially damaging voltage spikes in the vehicle electrical system that might occur if the voltage induced in the clutch coil windings could not be dissipated.

The compressor clutch engagement is controlled by several components: the heater-A/C controls in the passenger compartment, the A/C pressure transducer on the liquid line, the evaporator temperature sensor on the expansion valve, the Powertrain Control Module (PCM) in the engine compartment, and the compressor clutch relay in the Intelligent Power Module (IPM). The PCM may delay compressor clutch engagement for up to 30 seconds.