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.
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 (DRB III).
When additional coolant is needed, it should be added to the coolant pressure bottle. Use only 50/50 mix of Mopar 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, 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.
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 retained with a bolt. These 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 heater control head (ATC or MTC), the evaporator temperature sensor, the a/c pressure transducer, the compressor clutch relay, 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 located in the Power Distribution Center (PDC) in the engine compartment. Refer to the PDC label for relay identification and location.
The a/c compressor clutch relay is a electromechanical device that switches battery current to the a/c 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 (Manual Temperature Control, or Automatic Temperature Control) , the Body Control Module (BCM), and the a/c pressure transducer.
The compressor clutch relay cannot be repaired and, if faulty or damaged, it must be replaced.
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.
BLOWER MOTOR RESISTOR BLOCK
Vehicles with manual air conditioning (non-ATC) systems will have a blower motor resistor block. The resistor block is mounted to the lower right side of the HVAC housing in the passenger compartment, where it can be accessed for service.
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.
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.
Fig. 12 Evaporator Temperature Sensor Set Point:
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 set point 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 Set point table and for the correct setpoint.
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.
In-Car Sensor Aspirator Motor Operation:
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.
INSTRUMENT PANEL DEMISTER DUCTS
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.
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.
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-0 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.
A/C 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. This compressor uses an aluminum swash plate, teflon coated pistons and aluminum cylinder walls. One-way check valves are used to regulate refrigerant flow through the compressor.
CAUTION: A 10PA17 R-12 compressor looks identical to a 10PAI7 R134a and will bolt up to this vehicle. It is extremely important that a R-134a compressor is identified prior to using compressor in question. Check tag located on compressor for model number.
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.
A/C EXPANSION VALVE
The "H valve" type Thermal Expansion Valve (TXV) is located at the point where the refrigerant lines join the a/c evaporator 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.
RECEIVER / DRIER
The receiver/drier is located in the engine compartment near the dash panel on the passenger side of the vehicle. The receiver/drier incorporates a sight glass for visual diagnosis of the refrigerant system.
High-pressure liquid refrigerant from the condenser flows into the receiver/drier. A drying agent, called a desiccant, is used to remove any traces of moisture from the refrigerant system. The receiver/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 receiver/drier acts as a reservoir to store surplus refrigerant.
The A/C refrigerant must be removed from the system before removing the receiver/drier using a refrigerant recovery machine. Replace the receiver/drier if an A/C system is left open for an extended period of time.
The receiver/drier cannot be repaired and, if faulty, must be replaced.
REFRIGERANT
The refrigerant used in this air conditioning system is a HydroFluoroCarbon (HFC), type R-134a. Unlike R-12, which is a ChloroFluoroCarbon (CFC), R-134a refrigerant does not contain ozone-depleting chlorine. R-134a refrigerant is a non-toxic, non-flammable, clear, and colorless liquefied gas.
Even though R-134a does not contain chlorine, it must be reclaimed and recycled just like CFC-type refrigerants. This is because R-134a is a greenhouse gas and can contribute to global warming.
R-134a refrigerant is not compatible with R-12 refrigerant in an air conditioning system. Even a small amount of R-12 added to an R-134a refrigerant system will cause compressor failure, refrigerant oil sludge or poor air conditioning system performance. In addition, the PolyAlkylene Glycol (PAG) synthetic refrigerant oils used in an R-134a refrigerant system are not compatible with the mineral-based refrigerant oils used in an R-12 refrigerant system.
R-134a refrigerant system service ports, service tool couplers and refrigerant dispensing bottles have all been designed with unique fittings to ensure that an R-134a system is not accidentally contaminated with the wrong refrigerant (R-12). There are also labels posted in the engine compartment of the vehicle and on the compressor identifying to service technicians that the air conditioning system is equipped with R-134a.
REFRIGERANT OIL
The refrigerant oil used in R-134a refrigerant systems is a synthetic-based, PolyAlkylene Glycol (PAG), wax-free lubricant. Mineral-based R-12 refrigerant oils are not compatible with PAG oils, and should never be introduced to an R-134a refrigerant system.
There are different PAG oils available, and each contains a different additive package. The 10PA17 compressor used in this vehicle is designed to use an ND8 PAG refrigerant oil. Use only refrigerant oil of this same type to service the refrigerant system.
After performing any refrigerant recovery or recycling operation, always replenish the refrigerant system with the same amount of the recommended refrigerant oil as was removed. Too little refrigerant oil can cause compressor damage, and too much can reduce air conditioning system performance.
PAG refrigerant oil is much more hygroscopic than mineral oil, and will absorb any moisture it comes into contact with, even moisture in the air. The PAG oil container should always be kept tightly capped until it is ready to be used. After use, recap the oil container immediately to prevent moisture contamination.