Controls
CONTROLSA/C COMPRESSOR HIGH PRESSURE RELIEF VALVE
A high pressure relief valve is located on the compressor cylinder head, which is at the rear of the compressor. This mechanical valve is designed to vent refrigerant from the system to protect against damage to the compressor and other system components, caused by condenser air flow restriction or an overcharge of refrigerant.
The high pressure relief valve vents the system when a discharge pressure of 3445 - 4135 kPa (500 - 600 psi) or above is reached. The valve closes with a minimum discharge pressure of 2756 kPa (400 psi) is reached.
The high pressure relief valve vents only enough refrigerant to reduce the system pressure, and then re-seats itself. The majority of the refrigerant is conserved in the system. If the valve vents refrigerant, it does not mean the valve is faulty.
The high pressure relief valve is a factory-calibrated unit The valve cannot be adjusted or repaired and must not be removed or otherwise disturbed The valve is only serviced as a part of the compressor assembly
Fig.1 Compressor Clutch - Typical:
A/C COMPRESSOR CLUTCH
The compressor clutch assembly consists of a stationary electromagnetic coil a rotor bearing and rotor assembly and a clutch plate. The electromagnetic coil unit and the rotor bearing and rotor assembly are each retained on the nose of the compressor front housing with snap rings. The clutch plate is mounted to the compressor shaft and secured with a nut.
The compressor clutch assembly provides 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 rotor and drives the compressor shaft. When the coil is not energized, the rotor freewheels on the clutch rotor bearing, which is part of the rotor. 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 heater mode control switch, the a/c loss of charge switch, the a/c pressure transducer, the compressor clutch relay, the evaporator temperature sensor and the Powertrain Control Module (PCM). The PCM may delay compressor clutch engagement for up to 30 seconds.
A/C COMPRESSOR CLUTCH RELAY
The a/c 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 heater control, the a/c loss of charge switch, the a/c pressure transducer and the evaporator fin probe.
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.
Fig.14 A/C Heater Control:
A/C HEATER CONTROL
The a/c heater control is a completely electronic control head. The a/c heater system uses all 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 features, use, and suggested operation of these controls.
The a/c heater control is located to the right of the instrument cluster on the instrument panel. The a/c heater control contains a rotary-type temperature control knob, a rotary-type mode control knob, a rotary-type blower motor speed knob, and push buttons for a/c compressor and rear window defogger/heated mirror operation.
The a/c heater control is fully electronic, contains the logic and control circuits for the HVAC system, and is on the J1850 data bus.
The a/c heater control cannot be repaired. If faulty or damaged, the entire unit must be replaced. The illumination lamps are available for service replacement.
Fig.15 A/C Pressure Transduser:
A/C PRESSURE TRANSDUCER
This vehicle is equipped with an a/c pressure transducer. This transducer is screwed onto a fitting on the liquid line between the condenser and the high side refrigerant system service port.
The main function of the a/c pressure transducer is to disengage the compressor clutch when the refrigerant system high pressures are too high. The PCM senses a voltage from the transducer and converts it to a pressure. Based on this pressure, the PCM will disengage the clutch at 460 psi and re-engage the clutch at 290 psi. The a/c heater control also uses the pressure value to operate the auto-recirculation function for improved a/c performance under extreme conditions.
AMBIENT TEMP SENSOR
The ambient air temperature sensor is hardwired to the HVAC control and the HVAC control sends out a J1850 message to the overhead console. The ambient temperature sensor is a variable resistor mounted to a bracket that is secured with a screw to the right side of the radiator yoke, behind the radiator grille and in front of the engine compartment.
For complete circuit diagrams. The ambient temperature sensor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.
The ambient temperature sensor is a variable resistor that operates on a five-volt reference signal sent to it by the HVAC control head unit. The resistance in the sensor changes as temperature changes, changing the temperature sensor signal circuit voltage to the HVAC control head unit. Based upon the resistance in the sensor, the HVAC control head unit senses a specific voltage on the temperature sensor signal circuit, which it is programmed to correspond to a specific temperature.
BLEND DOOR ACTUATOR
The blend door actuator is a reversible, 12 volt Direct Current (DC), servo motor
The blend door actuator is interchangeable with 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 blend air door. The blend door actuator does not require mechanical indexing to the blend door linkage, as it is electronically calibrated by the Heater-A/C control module. The blend door actuator cannot be adjusted or repaired and if damaged or faulty it must be replaced.
The 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.
BLOWER MOTOR RESISTOR BLOCK
The blower motor resistor is mounted to the HVAC unit inside the passenger compartment. It can be accessed from the passenger foot well area. See Blower Motor Resistor in the Removal and Installation for more information.
The resistor has multiple resistor circuits 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 circuit to obtain the selected blower motor speed.
With the blower motor switch in the lowest speed position, the ground path for the motor is applied through all of the resistor circuits. Each higher speed selected with the blower motor switch applies the blower motor ground path through fewer of the resistor circuits, increasing the blower motor speed.
The blower motor resistor cannot be repaired and, if faulty or damaged, it must be replaced.
BLOWER MOTOR SWITCH
The Heater-A/C blower motor is controlled by a five position (OFF plus 4 speeds) rotary-type blower motor switch, mounted in the Heater-A/C control panel. The switch allows the selection of one of four blower motor speeds, but can only be turned off by selecting the OFF position with the Heater-A/C mode control switch knob.
The blower motor switch directs the blower motor ground path through the blower control switch to the blower motor resistor, as required to achieve the selected blower motor speed.
The blower motor switch cannot be repaired and, if faulty or damaged, the entire Heater-A/C control unit must be replaced. The blower motor switch knob is serviced separately.
MODE DOOR ACTUATOR
The mode door actuator is a reversible, 12-volt Direct Current (DC), servo motor. The single mode door actuator is located on the driver side end of the Heater-A/C housing unit, in the middle of the distribution housing. The mode door actuator is mechanically connected to the mode cam. The mode door actuator is interchangeable with the actuators for the blend air door(s) 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 mode door. The mode door actuator does not require mechanical indexing to the mode door linkage, as it is electronically calibrated by the Heater-A/C control module. The mode door actuator cannot be adjusted or repaired and, if damaged or faulty it must be replaced.
The mode 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 mode door actuator can move the mode cam 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 mode cam will move in one direction. When the module reverses the polarity of the voltage to the motor, the mode cam moves in the opposite direction. When the module makes the voltage to both connections high or both connections low, the mode cam 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 position of the mode actuator and the mode cam. The Heater-A/C control module learns the mode cam stop positions during the calibration procedure and will store a Diagnostic Trouble Code (DTC) for any problems it detects in the mode door actuator circuits. The mode door actuator can be diagnosed using a DRB III scan tool. Refer to the appropriate diagnostic information.
EVAPORATOR TEMPERATURE SENSOR
The evaporator temperature sensor is a temperature sensing element located at the coldest point on the face of the evaporator. Output from the probe is sampled by the HVAC Control Module. The evaporator temperature sensor is used to switch the A/C compressor clutch OFF before evaporator freeze-up occurs.
Output from the probe is sampled by the HVAC control module. The A/C compressor clutch is switched OFF/ON when the probe temperatures are near 0 °C (32 °F).
NOTE: Hysteresis and OFF/ON temperatures vary depending on the blower speed and software algorithm.
The evaporator temperature sensor prevents condensate water on the evaporator coil from freezing and obstructing A/C system air flow. The evaporator temperature sensor is non-repairable, and must be replaced if found faulty
RECIRCULATION DOOR ACTUATOR
The recirculation door actuator is a reversible, 12 volt Direct Current (DC), servo motor. The single recirculation door actuator is located on the passenger side end of the Heater-A/C housing unit, on the side of the intake air housing. The recirculation door actuator is mechanically connected to the recirculation air door. The recirculation door actuator is interchangeable with the actuators for the blend air door(s) and the mode 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 lower intake air housing. Each actuator also has an identical output shaft with splines that connects it to the linkage that drives the recirculation air door. The recirculation door actuator does not require mechanical indexing to the recirculation air door, as it is electronically calibrated by the Heater-A/C control module. The recirculation door actuator cannot be adjusted or repaired and, if damaged or faulty, it must be replaced.
The recirculation 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 recirculation door actuator can move the recirculation 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 recirculation air door will move in one direction. When the module reverses the polarity of the voltage to the motor, the recirculation air door moves in the opposite direction. When the module makes the voltage to both connections high or both connections low, the recirculation 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 position of the recirculation door actuator and the recirculation air door. The Heater-A/C control module learns the recirculation air door stop positions during the calibration procedure and will store a Diagnostic Trouble Code (DTC) for any problems it detects in the recirculation door actuator circuits. The recirculation door actuator can be diagnosed using a DRB III scan tool. Refer to the appropriate diagnostic information.