Heating and Air Conditioning: Description and Operation
ENGINE COOLING SYSTEM REQUIREMENTSTo maintain the performance level of the HVAC system, the engine cooling system must be properly maintained. Refer to Cooling for more information.
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 the cooling system. Coolant temperature can be checked using the scan tool (DRBIII).
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 I to Lubrication and Maintenance for service schedules.
CAUTION:
- Do not add additional inhibitors, anti-rust products, or soluble oil (sold as "water pump lubricants"). These products may not be compatible with the engine coolant.
Refer to Cooling for cooling system procedures.
IN-CAR TEMPERATURE SENSOR
Fig.14 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 aspirator motor assembly, and the second part is a temperature thermistor. The in-car sensor aspirator motor 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. The in-car sensor aspirator motor is part of the ATC Control and not a separate serviceable part. The ATC Control must be replaced if there is a fault relating to the motor. The in-car temperature sensor thermistor is part of the ATC Control and not a separate serviceable part. One must replace the ATC Control if the ATC self-diagnostics indicates a fault code.
Air drawn from the passenger compartment by the in-car sensor aspirator motor assembly, and 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 In-Car Sensor Aspirator Motor Operation table for when the ATC Sensor is operating.
BLEND DOOR ACTUATOR
The blend door actuator is an electric motor which mechanically positions the blend door. A potentiometer in the actuator allows the BCM (for both manual and ATC systems) 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 an electric motor. It mechanically positions the panel/bi-level door and the floor/defrost door. This actuator contains a potentiometer which allows the BCM (for both manual and ATC systems) to know the exact position of the mode doors at all times. The mode door actuator is not serviceable and must be replaced if found to be defective.
Fig.19 ATC 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.
DISTRIBUTION
HVAC 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 HVAC unit housing and passes through the evaporator. At this point airflow can be directed either through or around the heater core.
Airflow temperature can be adjusted by the blend door with the TEMP control on the a/c heater control. After the air passes the blend 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 a/c heater control.
Ambient air intake can be shut off by closing the recirculation door. This will recirculate the air that is already inside the vehicle. See owners manual for recirculation operation.
HVAC FORCED RECIRCULATION
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.
BLOWER MOTOR
The blower motor and blower wheel are located in the passenger side end of the HVAC housing, below the glove box module. The blower motor controls the velocity of the air flowing through the HVAC housing by spinning a squirrel cage-type blower wheel within the housing at the selected speed. The blower motor and blower wheel can be serviced from the passenger compartment side of the housing.
The blower motor will only operate when the ignition switch is in the On position, and the a/c heater mode control switch is in any position, except off. The blower motor circuit is protected by a fuse in the junction block. On models with the standard manual temperature control system, the blower motor speed is controlled by regulating the battery feed through the blower motor switch and the blower motor resistor. On models with Automatic Temperature Control (ATC) system, the blower motor speed is controlled by using a linear blower controller with a pulse width modulation input. The blower motor power module adjusts the battery feed voltage to the blower motor, based upon an input from the blower motor switch, through the ATC control module. Pulse width modulation of blower power allows the blower to operate at any speed from stationary to full speed.
The blower motor and blower motor wheel cannot be repaired, and if faulty or damaged, they must be replaced. The blower motor and blower wheel are not serviced separately and must be replaced as an assembly.
PLUMBING
REFRIGERANT LINE
The refrigerant lines and hoses are used to carry the refrigerant between the various air conditioning system components. A barrier hose design with a nylon tube, which is sandwiched between rubber layers, is used for the R-134a air conditioning system on this vehicle. This nylon tube helps to further contain the R-134a refrigerant, which has a smaller molecular structure than R-12 refrigerant. The ends of the refrigerant hoses are made from lightweight aluminum or steel, and commonly use braze-less fittings.
Any kinks or sharp bends in the refrigerant plumbing will reduce the capacity of the entire air conditioning system. Kinks and sharp bends reduce the flow of refrigerant in the system. A good rule for the flexible hose refrigerant lines is to keep the radius of all bends at least ten times the diameter of the hose. In addition, the flexible hose refrigerant lines should be routed so they are at least 80 millimeters (3 inches) from the exhaust manifold (Whenever possible).
High pressures are produced in the refrigerant system when the air conditioning compressor is operating. Extreme care must be exercised to make sure that each of the refrigerant system connections is pressure-tight and leak free. It is a good practice to inspect all flexible hose refrigerant lines at least once a year to make sure they are in good condition and properly routed.
The refrigerant lines and hoses are coupled with other components of the HVAC system with peanut- block style fittings. A stat-O seal type flat steel gasket with a captured compressible O-ring, is used to mate plumbing lines with A/C components to ensure the integrity of the refrigerant system.
The refrigerant lines and hoses cannot be repaired and, if faulty or damaged, they must be replaced.