DESCRIPTION
An Automatic Temperature Controlled (ATC) single zone type heating-A/C system is standard on this model.
To maintain the performance level of the heating, ventilation and air conditioning (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 A/C condenser will reduce the performance of the A/C and engine cooling systems.
The engine cooling system includes the radiator, thermostat, radiator hoses and the engine coolant pump. Refer to ENGINE COOLING SYSTEM for more information before opening or attempting any service to the engine cooling system.
Scheme 2
All vehicles are equipped with a common heater, ventilation and air conditioning (HVAC) housing (1). The heating-A/C system combines A/C, heating, and ventilating capabilities in a single HVAC housing mounted within the passenger compartment beneath the instrument panel. The HVAC housing includes
- A/C evaporator (2)
- Mode-air doors (3)
- Mode door actuator (4)
- Recirculation-air door and actuator (5)
- Particulate air filter (when equipped) (6)
- Blower motor (7)
- Blower motor power module (8)
- Blend door actuator (9)
- Heater core (10)
- Evaporator temperature sensor (11)
- Blend-air door (12)
Based upon the system mode selected, conditioned air can exit the HVAC housing through one or a combination of the three main housing outlets: defrost, panel or floor. The defrost and panel outlets are located on the top of the HVAC air distribution housing and the floor outlets are located on each side of the distribution housing. Once the conditioned air exits the HVAC housing, it is further directed through molded plastic ducts to the various outlets within the vehicle interior. These outlets and their locations are as follows
- Defroster Outlet - Two defroster outlets are located in the center of the instrument panel, near the base of the windshield.
- Side Window Demister Outlets - There are two side window demister outlets, one is located at each outboard end of the instrument panel, near the A-pillars.
- Panel Outlets - There are four panel outlets in the instrument panel, one located near each outboard end of the instrument panel facing the rear of the vehicle and two located near the top of the instrument panel center bezel.
- Front Floor Outlets - There are two front floor outlets, one located on each side the floor panel center tunnel behind the instrument panel.
- Rear Seat Floor Outlets - There are two rear seat floor outlets, one located on each side of the floor panel near the front of each rear seat foot well.
OPERATION
The Automatic Temperature Controlled (ATC) heating-A/C system is a blend-air type system. In a blend-air system, a blend-air door controls the amount of conditioned air that is allowed to flow through, or around the heater core. This design allows almost immediate control of output air temperature.
Scheme 3
Note. Typical blend-air type HVAC system shown in illustration.
The heating-A/C system pulls outside (ambient) air through the fresh air intake (4) located at the cowl panel at the base of the windshield and into the air inlet housing above the heating, ventilation and air conditioning (HVAC) housing and passes through the A/C evaporator (7). Air flow is then directed either through or around the heater core (2). This is done by adjusting the position of the blend-air door (3) with the temperature control located on the A/C-heater control in the instrument panel. Air flow is then directed out the floor outlet (8), instrument panel outlet (10) or the defroster outlet (1) in various combinations by adjusting the position of the mode-air doors (9 and 11) using the mode control located on the A/C-heater control. The temperature and mode control uses electrical actuators to operated the air doors.
The velocity of the air flow out of the outlets can be adjusted with the blower speed control located on the A/C-heater control.
The fresh air intake can be shut off by pressing the Recirculation button on the A/C-heater control. This will operate the electrically actuated recirculation-air door (5), which closes off the fresh air intake. With the fresh air intake closed, the conditioned air within the vehicle is pulled back into the HVAC housing through the recirculation air intake (6).
The A/C compressor can be engaged by pressing the A/C (snowflake) button on the A/C-heater control. It will automatically engage when the mode control is set in any Mix to Defrost position. This will remove heat and humidity from the air before it is directed through or around the heater core. The mode control on the A/C-heater control is used to direct the conditioned air to the selected system outlets.
The front and rear floor outlets receive airflow from the HVAC housing through the front and rear floor ducts. The front floor outlets are integral to the molded plastic front floor ducts, which are secured to each side of the HVAC housing. Two molded plastic rear seat ducts are attached to the two molded plastic rear floor ducts, which are secured to the rear of the HVAC housing. The rear seat ducts direct airflow beneath the carpet to the outlets located near the front of each rear seat foot well. None of the floor outlets can be adjusted.
The panel outlets receive airflow from the HVAC housing through a single molded plastic panel outlet duct, which is secured to the top of the instrument panel. The airflow from each of the panel outlets is adjustable. A thumbwheel located on each panel outlet is used to adjust a diffuser that changes the airflow direction, and each panel outlet grille has a shutter that opens or closes to turn airflow on or off through that outlet.
The defroster outlets receive airflow from the HVAC housing through the molded plastic defroster duct, which is secured to the top of the instrument panel. The airflow from the defroster outlets is directed by fixed vanes in the defroster outlet grilles and cannot be adjusted.
The side window demister outlets receive airflow from the HVAC housing through the defroster duct and molded plastic demister ducts, which are also secured to the top of the instrument panel. The airflow from the side window demister outlets is directed by fixed vanes and cannot be adjusted. The side window demister outlet grilles are integral to the instrument panel outlets and direct air from the HVAC housing through the outlets on the top corners of the instrument panel. The demisters operate when the mode control is set in any Floor to Defrost position.
The blend door actuator is connected to the A/C-heater control through the vehicle electrical system by a dedicated two-wire lead and connector of the instrument panel wire harness. The blend door actuator can move the blend-air door in two directions. When the A/C-heater control 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 A/C-heater control reverses the polarity of the voltage to the motor, the blend-air door moves in the opposite direction. Once the A/C-heater control makes the voltage to both connections high or both connections low, the blend-air door stops and will not move.
The A/C-heater control uses a pulse-count positioning system to monitor the operation and relative position of the blend door actuator and the blend-air door. The A/C-heater control 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. For more information, refer to the appropriate Electrical Diagnostic article.
The blend door actuator cannot be adjusted or repaired and it must be replaced if found inoperative or damaged.
The mode door actuator (1) for the heating-A/C system is a reversible, 12-volt Direct Current (DC) servo motor, which is mechanically connected to the mode-air doors. The mode door actuator is located on the right side of the HVAC air distribution housing.
The mode door actuator is contained within a black molded plastic housing with an integral wire connector receptacle (2). An output shaft with splines (3) connect it to mode door linkage and integral mounting tabs (4) allow the actuator to be secured to the air distribution housing. The mode door actuator does not require mechanical indexing to the mode-air doors, as it is electronically calibrated by the A/C-heater control.
The A/C-heater control must be recalibrated each time an actuator motor is replaced. Refer to the appropriate Electrical Diagnostic article. .
The mode door actuator is interchangeable with the actuators for the recirculation and blend-air doors.
The mode door actuator is connected to the A/C-heater control through the vehicle electrical system by a dedicated two-wire lead and connector of the instrument panel wire harness. The mode door actuator can move the mode-air door in two directions. When the A/C-heater control pulls the voltage on one side of the motor connection high and the other connection low, the mode-air door will move in one direction. When the A/C-heater control reverses the polarity of the voltage to the motor, the mode-air door moves in the opposite direction. Once the A/C-heater control makes the voltage to both connections high or both connections low, the mode-air door stops and will not move.
The A/C-heater control uses a pulse-count positioning system to monitor the operation and relative position of the mode door actuator and the mode-air door. The A/C-heater control learns the mode-air door 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. Refer to the appropriate Electrical Diagnostic article. .
The mode door actuator cannot be adjusted or repaired and it must be replaced if inoperative or damaged.
The recirculation door actuator (1) is a reversible, 12 volt direct current (DC) servo motor, which is connected directly to the pivot shaft lever of the recirculation-air door. The recirculation door actuator is located on the right side of the HVAC air inlet housing.
The recirculation door actuator is contained within a black molded plastic housing with an integral wire connector receptacle (2), an output shaft with splines (3) connect it to the recirculation door and three integral mounting tabs (4) allow the actuator to be secured to the air inlet housing. The recirculation door actuator does not require mechanical indexing to the recirculation-air door, as it is electronically calibrated by the A/C-heater control.
The A/C-heater control must be recalibrated each time an actuator motor is replaced. Refer to the appropriate Electrical Diagnostic article. .
The recirculation door actuator is interchangeable with the actuators for the blend and mode-air doors.
The recirculation door actuator is connected to the A/C-heater control through the vehicle electrical system by a dedicated two-wire lead and connector of the instrument panel wire harness. The recirculation door actuator can move the recirculation-air door in two directions. When the A/C-heater control 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 A/C-heater control reverses the polarity of the voltage to the motor, the recirculation-air door moves in the opposite direction. Once the A/C-heater control makes the voltage to both connections high or both connections low, the recirculation-air door stops and will not move.
The A/C-heater control uses a pulse-count positioning system to monitor the operation and relative position of the recirculation door actuator and the recirculation-air door. The A/C-heater control 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. Refer to the appropriate Electrical Diagnostic article. .
The recirculation door actuator cannot be adjusted or repaired and it must be replaced if inoperative or damaged.
The blower motor power module is connected to the vehicle electrical system through a dedicated lead and connector of the instrument panel wire harness. A second lead and connector of the instrument panel wire harness is connected to the blower motor. The blower motor power module allows the microprocessor-based automatic temperature control (ATC) A/C-heater control to calculate and provide infinitely variable blower motor speeds based upon either manual blower switch input or the ATC programming using a pulse width modulated (PWM) circuit strategy.
The PWM voltage is applied to a comparator circuit which compares the PWM signal voltage to the blower motor feedback voltage. The resulting output drives the power module circuitry, which provides a linear output voltage to change or maintain the desired blower speed.
The blower motor power module is diagnosed using a scan tool. Refer to the appropriate Electrical Diagnostic article. .
The blower motor power module cannot be adjusted or repaired must be replaced if inoperative or damaged.
The evaporator temperature sensor monitors the surface temperature of A/C evaporator and supplies an input signal to the A/C-heater control. The A/C-heater control uses the evaporator temperature sensor input signal to optimize A/C system performance and to protect the A/C system from evaporator freezing. The evaporator temperature sensor will change its internal resistance in response to the temperatures it monitors and is connected to the A/C-heater control through sensor ground circuit and a 5-volt reference signal circuit. As the temperature of the A/C evaporator decreases, the internal resistance of the evaporator temperature sensor decreases.
The A/C-heater control uses the monitored voltage reading as an indication of evaporator temperature. The A/C-heater control is programmed to respond to this input by requesting the powertrain control module (PCM) to adjust the compressor swash plate angle as necessary to optimize A/C system performance and to protect the A/C system from evaporator freezing. Refer to COMPRESSOR, A/C, OPERATION .
The evaporator temperature sensor is diagnosed using a scan tool.
The evaporator temperature sensor cannot be adjusted or repaired and it must be replaced if inoperative or damaged.
The infrared sensor detects thermal radiation emitted by the driver and front passenger seat occupants and surroundings and converts its data into a linear Pulse Width Modulated (PWM) output signal which is read by the Automatic Temperature Control (ATC) A/C-heater control. The ATC A/C-heater control uses the infrared sensor data as one of the inputs necessary to automatically control the interior cabin temperature levels. By using thermal radiation (surface temperature) measurement, rather than an air temperature measurement, the ATC heating-A/C system is able to adjust itself to the comfort level as perceived by the occupants. This allows the ATC system to compensate for other ambient conditions affecting comfort levels, such as solar heat gain or evaporative heat loss.
The ATC system logic responds to the infrared sensor message by calculating and adjusting the air flow temperature and air flow rate needed to properly obtain and maintain the selected comfort level temperature of the occupants. The A/C-heater control continually monitors the infrared sensor circuits, and will store Diagnostic Trouble Codes (DTCs) for any problem it detects.
The infrared sensor is diagnosed using a scan tool. Refer to the appropriate Electrical Diagnostic article. .
The infrared sensor cannot be adjusted or repaired and must be replaced if inoperative or damaged.
The Automatic Temperature Control (ATC) heating and A/C system uses two sun sensors to balance the system in response to side-to-side variations of sun light intensity. Passengers in sun and shadow require different functional settings because they experience very different temperatures. The sun sensor assembly provides data to the A/C heater control to help determine proper mode and blend-air door positions and blower motor speeds. The sun sensors are not thermistor type sensors, but rather photo diodes. For this reason the sun sensors responds to sun light intensity rather than temperature. The sun sensor assembly is also used to sense day and night conditions for automatic headlight control, if equipped.
The sun sensor is diagnosed using a scan tool. Refer to the appropriate Electrical Diagnostic article. .
The sun sensor assembly cannot be adjusted or repaired and must be replaced if inoperative or damaged.
The A/C pressure transducer monitors the pressures in the high side of the refrigerant system through its connection to a fitting on the A/C discharge line. The internal resistance of the A/C pressure transducer changes in response to the pressures it monitors. The Totally Integrated Power Module (TIPM) provides a five volt reference signal and a sensor ground to the A/C pressure transducer. The TIPM then monitors the output voltage of the transducer on a sensor return circuit to determine refrigerant pressure and sends a message to the Powertrain Control Module (PCM) over the Controller Area Network (CAN) C BUS. The PCM is programmed to respond to this and other sensor inputs by controlling the operation of the swash plate within the A/C compressor and the radiator cooling fan to help optimize A/C system performance and to protect the system components from damage. The PCM adjusts the swash plate to nearly a zero degree angle (low compressor displacement) when high side pressure rises above 3130 kPa (454 psi) and readjusts the swash plate to a greater angle (higher compressor displacement) when high side pressure drops below 1999 kPa (290 psi). The A/C pressure transducer also reduces the swash plate angle if the high side pressure drops below 200 kPa (29 psi) and will increase the swash plate angle when the high side pressure rises above 234 - 262 kPa (34 - 38 psi). When the refrigerant pressure rises above 1655 kPa (240 psi) the PCM will actuate the cooling fan.
A Schrader-type valve in the A/C discharge line fitting permits the A/C pressure transducer to be removed or installed without disturbing the refrigerant in the A/C system.
The A/C pressure transducer is diagnosed using a scan tool. Refer to the appropriate Electrical Diagnostic article. .
The A/C pressure transducer cannot be adjusted or repaired and must be replaced if inoperative or damaged.
The blower motor controls the velocity of air moving through the HVAC housing by spinning the blower wheel within the HVAC air inlet housing at the selected speed.
The Automatic Temperature Control (ATC) heating and A/C system uses an electronic blower motor power module to control blower motor speed. The power module uses a Pulse Width Modulated (PWM) input from the A/C heater control and a feedback signal from the blower motor to regulate the blower motor ground path. The blower motor receives battery current through the Totally Integrated Power Module (TIPM) whenever the ignition is in RUN, and the blower motor control is in any position except Off.
The blower motor control system is diagnosed using a scan tool. Refer to the appropriate Electrical Diagnostic article. .
The blower motor and blower motor wheel are factory balanced and cannot be adjusted or repaired and must be replaced as an assembly if inoperative or damaged.
Possible causes of an inoperative blower motor include
- Open fuse
- Inoperative blower motor power module
- Inoperative blower motor switch
- Inoperative blower motor
- Inoperative blower motor circuit wiring or wire harness connectors
When air passes through the fins of the A/C condenser, the high-pressure refrigerant gas within the A/C condenser gives up its heat. The refrigerant then condenses as it leaves the A/C condenser and becomes a high-pressure liquid. The volume of air flowing over the condenser fins is critical to the proper cooling performance of the A/C system. Therefore, it is important that there are no objects placed in front of the radiator grille openings at the front of the vehicle or foreign material on the condenser fins that might obstruct proper air flow. Also, any factory-installed air seals or shrouds must be properly reinstalled following radiator or A/C condenser service.
Note. Replacement of the refrigerant line O-ring seals and gaskets is required anytime a refrigerant line is disconnected. Failure to replace the rubber O-ring seals and metal gaskets could result in a refrigerant system leak.
The A/C condenser has no serviceable parts. The O-ring seals used on the connections are made from a special type of rubber not affected by R-134a refrigerant. The O-ring seals and gaskets must be replaced whenever a refrigerant line is disconnected from the A/C condenser.
The A/C condenser cannot be repaired and must be replaced if leaking or damaged.
Note. LHD model shown in illustration. RHD model similar.
Scheme 4
The heater core (1) for the heating-A/C system is mounted within the HVAC air distribution housing, which is located behind the instrument panel. The heater core is a heat exchanger made of rows of tubes with fins and is positioned within the air distribution housing so that only the selected amount of air entering the housing passes through the heater core before it is distributed through the heating-A/C system ducts and outlets. One end of the heater core is fitted with a tank (2) that includes the fittings for the heater core tubes (3).
The heater core can only be serviced by removing the HVAC housing from the vehicle.
Engine coolant is circulated through the heater hoses to the heater core at all times. As the coolant flows through the heater core, heat is removed from the engine and is transferred to the heater core tubes and fins. Air directed through the heater core picks up the heat from the heater core fins. The blend-air door allows control of the heater output air temperature by regulating the amount of air flowing through the heater core. The blower motor speed controls the volume of air flowing through the HVAC housing.
The heater core cannot be repaired and it must be replaced if inoperative, leaking or damaged.
Refrigerant enters the A/C evaporator through the A/C orifice tube as a low-temperature, low-pressure mixture of liquid and gas. As air flows over the fins of the A/C evaporator, the humidity in the air condenses on the fins, and the heat from the air is absorbed by the refrigerant. Heat absorption causes the refrigerant to boil and vaporize. The refrigerant becomes a low-pressure gas when it leaves the A/C evaporator.
Note. Replacement of the refrigerant line O-ring seals and gaskets is required anytime a refrigerant line is disconnected. Failure to replace the rubber O-ring seals and metal gaskets could result in a refrigerant system leak.
The A/C evaporator has no serviceable parts except for the O-ring seals. The O-ring seals used on the connections are made from a special type of rubber not affected by R-134a refrigerant.
The A/C evaporator cannot be repaired and must be replaced if leaking or damaged.
The variable A/C orifice tube provides improved A/C system cooling during city driving and when under heavy loads by controlling refrigerant flow through the two parallel flow paths integral to the orifice tube. Under normal loads, the refrigerant flows through the inlet filter screen, the fixed and variable ports and both metering orifices. As the load on the A/C system increases, the temperature of the refrigerant leaving the A/C condenser increases, which causes the bi-metal coil to expand and restrict the flow of refrigerant through the variable port of the tube. Restricting the flow of refrigerant through the variable port and its orifice provides a greater pressure differential between the high and low pressure sides of the A/C system, resulting in colder refrigerant vapor traveling through the A/C evaporator to help remove the heat from the conditioned air flowing into the passenger compartment.
The A/C orifice tube is not serviceable and the A/C liquid line must be replaced if the orifice tube is found inoperative.
Scheme 5
- Pull back the floor carpet to gain access to the condensation drain tube (2) located on the left side of the vehicle at the front right of the foot well. Refer to «CARPET, FLOOR, REMOVAL»(ref-485483-S31801773972012071300000) .
- Disconnect the condensation drain tube from the bottom of the HVAC housing (1).
- Remove the condensate drain tube from the rubber grommet (3) in the front floor panel (4).
- If required, remove the rubber grommet from the floor panel.