System Overveiw
(ATC) System = R134a w/expansion valve(Manual) System = R134a w/expansion valve
ATC In-Car Temperature Sensor:
ATC IN-CAR TEMPERATURE SENSOR
The Automatic Temperature Control (ATC) In-Car Temperature Sensor returns electrical signals to the Body Control Module (BCM). The In-Car Temperature Sensor is used on ATC equipped vehicles only. The In-Car Temperature Sensor is made up of two parts. One part is the in-car sensor motor fan assembly and the second part is a temperature thermistor. The in-car sensor motor fan assembly attaches to the back of the ATC Control head. This assembly has a small fan and a motor which draws air through the intake on the front of the ATC control. The in-car sensor thermistor is located inside of the ATC Control Head. Air drawn from the passenger compartment by the in-car sensor motor-fan assembly, flows over the thermistor. The in-car sensor thermistor changes resistance with air temperature. The BCM measures this resistance and calculates the temperature of the air drawn into the ATC Control. The ATC system then makes adjustments to maintain the optimum passenger compartment comfort. Refer to the ATC Sensor Motor-Fan Operation table for when the ATC Sensor is operating.
ATC SENSOR MOTOR-FAN OPERATION
The in-car sensor motor is an integral part of the Control Head and not a separate serviceable part. The ATC Control Head must be replaced if there is a fault relating to the motor. See Diagnosis and Testing for proper check of airflow. The In-Car Sensor Thermistor is part of the ATC Control Head and not a separate serviceable part. One must replace the ATC Control Head if the ATC self-diagnostics indicates a fault code. See Self-Diagnostics for information on diagnosing wiring and thermistor.
BLOWER MOTOR RESISTOR
Vehicles with manual air conditioning (non-ATC) systems will have a blower motor resistor. The 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. See Blower Motor Resistor in the Removal and Installation for more information.
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 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.
BLOWER MOTOR POWER MODULE
The blower motor power module is only used in vehicles equipped with Automatic Temperature Control (ATC). It is located on the lower right side of the HVAC unit housing, and is controlled by the Body Control Module (BCM).
The power module receives pulse width modulated (PWM) signals from the BCM. The power module varies voltage to the blower motor for different blower speeds based on the ATC software. There are 14 selectable speeds, while the Auto mode provides 256 variations.
COMPRESSOR
The air conditioning system uses a Nippondenso 10PA17 ten cylinder, double-acting swash plate-type compressor on all models. This compressor has a fixed displacement of 170 cubic centimeters (10.374 cubic inches), and has both the suction and discharge ports located on the cylinder head. A label identifying the use of R-134a refrigerant is located on the compressor.
The compressor is driven by the engine through an electric clutch, drive pulley and belt arrangement. The compressor is lubricated by refrigerant oil that is circulated throughout the refrigerant system with the refrigerant.
The compressor draws in low-pressure refrigerant vapor from the evaporator through its suction port. It then compresses the refrigerant into a high-pressure, high-temperature refrigerant vapor, which is then pumped to the condenser through the compressor discharge port.
The compressor cannot be repaired. If faulty or damaged, the entire compressor assembly must be replaced. The compressor clutch, pulley and clutch coil are available for service.
ENGINE COOLING SYSTEM REQUIREMENTS
To maintain the performance level of the heating/ air-conditioning system, the engine cooling system must be prepared as shown.
The use of a bug screen is not recommended. Any obstructions in front of the radiator or condenser can reduce the performance of the A/C and/or engine cooling system.
WARNING: DO NOT OPEN COOLING SYSTEM WHEN HOT AS PERSONAL INJURY OR DAMAGE TO VEHICLE MAY RESULT.
The engine cooling system is designed to develop internal pressure of 97 to 123 kPa (14 to 18 psi). Wait 15 minutes (after the engine is shut off), or until safe temperature and pressure is attained, before opening cooling system. Coolant temperature can be checked using the scan tool (DRB III).
When additional coolant is needed, it should be added to the coolant pressure bottle. Use only 50/50 mix of Mopar (R) Antifreeze/Coolant, 5 Year/100,000 Mile Formula (orange in color), or the equivalent and distilled water. This coolant must not be mixed with other (green in color) coolants. If this occurs, a reduction in the extended service interval will result. Refer to LUBRICATION AND MAINTENANCE for service schedules.
CAUTION: Do not add additional inhibitors, antirust products, or soluble oil (sold as "water pump lubricants"). These products may not be compatible with the engine coolant.
EVAPORATOR TEMPERATURE SENSOR
The evaporator temperature sensor is a temperature sensing element located at the coldest point on the face of the evaporator. The evaporator temperature sensor prevents condensate water on the evaporator coil from freezing which can block airflow. The probe is a thermistor inside a metal tube which is wedged between the evaporator fins, The metal tube is tightly held by the evaporator fins so that the thermistor in the tube will detect the temperature of the evaporator. The thermistor will change resistance as the temperature changes.
Evaporator Temperature Sensor Setpoint:
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.
EXPANSION VALVE
The "H valve" type thermal expansion valve (TXV) is located at the point where the refrigerant lines join the evaporator coil on the engine compartment side of the dash panel.
The expansion valve is a factory calibrated unit and cannot be adjusted or repaired. If faulty or damaged, the expansion valve must be replaced.
High-pressure, high temperature liquid refrigerant from the liquid line passes through the expansion valve orifice, converting it into a low-pressure, low- temperature mixture of liquid and gas before it enters the evaporator Coil. A temperature sensor in the expansion valve control head monitors the temperature of the refrigerant leaving the evaporator coil through the suction line, and adjusts the orifice size at the liquid line to let the proper amount of refrigerant into the evaporator coil to meet the vehicle cooling requirements. Controlling the refrigerant flow through the evaporator ensures that none of the refrigerant leaving the evaporator is still in a liquid state, which could damage the compressor.
FILTER-DRIER
The filter-drier is located in the engine compartment near the dash panel on the passenger side of the vehicle. The filter-drier incorporates a sight glass for visual diagnosis of the refrigerant system
High-pressure liquid refrigerant from the condenser flows into the filter-drier. A drying agent, called a desiccant, is used to remove any traces of moisture from the refrigerant system. The filter-drier also performs a filtering action to prevent foreign material in the refrigerant from contaminating the expansion valve. In addition, during periods of high demand air conditioner operation, the filter-drier acts as a reservoir to store surplus refrigerant.
The A/C refrigerant must be removed from the system before removing the filter/drier using a refrigerant recovery machine. Replace the filter/drier if an A/C system is left open for an extended period of time.
The filter-drier cannot be repaired and, if faulty, must be replaced.
HANDLING TUBING AND FITTINGS
Kinks in the refrigerant tubing or sharp bends in the refrigerant hose lines will greatly reduce the capacity of the entire system.
CAUTION: The system must be completely empty before opening any fitting or connection in the refrigeration system. Open fittings with caution even after the system has been emptied. If any pressure is noticed as a fitting is loosened, retighten fitting and evacuate the system again.
A good rule for the flexible hose lines is to keep the radius of all bends at least 10 times the diameter of the hose. Sharper bends will reduce the flow of refrigerant. The flexible hose lines should be routed so they are at least 3 inches (80 mm) from the exhaust manifold. Inspect all flexible hose lines to make sure they are in good condition and properly routed.
The use of correct wrenches when making connections is very important. Improper wrenches or improper use of wrenches can damage the fittings.
The internal parts of the A/C system will remain stable as long as moisture-free refrigerant and refrigerant oil is used. Abnormal amounts of dirt, moisture or air can upset the chemical stability. This may cause operational troubles or even serious damage if present in more than very small quantities.
When opening a refrigeration system, have everything you will need to repair the system ready. This will minimize the amount of time the system must be opened. Cap or plug all lines and fittings as soon as they are opened. This will help prevent the entrance of dirt and moisture. All new lines and components should be capped or sealed until they are ready to be used.
All tools, including the refrigerant dispensing manifold, the manifold gauge set, and test hoses should be kept clean and dry.
High pressures are produced in the system when it is operating. Extreme care must be exercised to make sure that all connections are pressure tight. Dirt and moisture can enter the system when it is opened for repair or replacement of lines or components. The refrigerant oil will absorb moisture readily out of the air. This moisture will convert into acids within a closed system.
HVAC FORCED RECIRCULATION
The HVAC system (both Manual A/C and ATC) may force itself into recirculated airflow when extremely hot outside ambient conditions exist. This action can occur at a range of approximately 95 °F to 120 °F.
The Body Control Module (BCM) receives a Programmable Communications Interface (PCI) bus message from the Powertrain Control Module (PCM) with the feedback from the A/C Pressure Transducer. The BCM will force the system into the Recirculation mode, reducing the A/C refrigerant pressure under these extreme conditions. The reduced operating pressure offers improved A/C system performance and reduced wear on A/C components.
REFRIGERANT LINES
The air conditioning lines used on this vehicle are made from reinforced rubber with a nylon liner on the inner walls. The ends of the A/C lines are made with light weight aluminum fittings.
CAUTION: Never attempt to disconnect an A/C line without reclaiming all refrigerant from the air conditioning system. The system must be empty.
The O-rings are made from a special type of rubber that is not affected by R-134a refrigerant. O-ring replacement is required whenever lines are removed and installed. Use only O-rings specified for this vehicle. Failure to use the correct type of O-ring will cause the connection to leak within a short period of time.
When it is necessary to open the refrigeration system, have everything needed to service the system ready. The system should not be left open any longer than necessary. Cap or plug all lines and fittings as soon as they are opened. This will prevent the entrance of dirt and moisture into the system. All new lines and components should be capped or sealed until they are ready to be used.
WARNING:
- AVOID BREATHING A/C REFRIGERANT AND LUBRICANT VAPOR OR MIST. EXPOSURE MAY IRRITATE EYES, NOSE AND THROAT. USE ONLY APPROVED SERVICE EQUIPMENT MEETING SAE REQUIREMENTS TO DISCHARGE R-134a SYSTEM. IF ACCIDENTAL SYSTEM DISCHARGE OCCURS, VENTILATE WORK AREA BEFORE RESUMING SERVICE.
- R-134a SERVICE EQUIPMENT OR VEHICLE A/C SYSTEM SHOULD NOT BE PRESSURE TESTED OR LEAK TESTED WITH COMPRESSED AIR. SOME MIXTURES OF AIR/R-134a HAVE BEEN SHOWN TO BE COMBUSTIBLE AT ELEVATED PRESSURES. THESE MIXTURES ARE POTENTIALLY DANGEROUS AND MAY RESULT IN FIRE OR EXPLOSION CAUSING INJURY OR PROPERTY DAMAGE.
SIDE WINDOW DEMISTERS
The side window demisters direct air from the heater assembly through the outlets located on the top corners of the instrument panel, to the side windows.
Side window demisting is performed when the mode selector is on FLOOR, DEFROST, MIX OR BI-LEVEL setting.
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.
SYSTEM AIRFLOW
The system draws outside air through the cowl opening at the base of the windshield. Then it goes into the plenum chamber above the Heater A/C unit housing and passes through the evaporator. At this point airflow can be directed either through or around the heater core.
Airflow can be adjusted by the blend-air door with the TEMP control on the control head. After the air passes the blend air door, the air flow is then directed from the PANEL, BI-LEVEL (panel and floor), and FLOOR-DEFROST outlets. Air flow velocity can be adjusted with the blower speed selector switch on the control head.
Ambient air intake can be shut off by closing the recirculating air door. This will recirculate the air that is already inside the vehicle. See owners manual for recirculation operation.