Component Description
Heating Ventilation Air Conditioning (HVAC) Control Module - Electronic Automatic Temperature Control (EATC)
The EATCHVAC control module is on the MS-CAN and sets DTCs. A/C requests are sent to the GWM and then to the PCM via the HS-CAN1.
The temperature control switch adjusts the discharge air temperature. Movement of the temperature knob from cool to warm causes a corresponding movement of the temperature door. The position of the temperature door determines the discharge air temperature. The temperature control selector is an integral part of the HVAC control module and cannot be serviced separately.
The airflow mode setting adjusts the discharge air outlet location. Each airflow mode selector icon causes a corresponding movement of the airflow mode doors and determines the discharge air outlet location. The airflow mode selector knob is an integral part of the HVAC control module and cannot be serviced separately.
The A/C button determines A/C compressor operation, except when the temperature selector is set to MAX A/C or the airflow mode selector is in Defrost mode. The A/C button is an integral part of the HVAC control module and cannot be serviced separately.
The recirculated air request button can be activated in any mode except Defrost. In MAX A/C mode the recirculated air indicator is illuminated (recirculated air forced on). The recirculated air request button is an integral part of the HVAC control module and cannot be serviced separately.
Heating Ventilation Air Conditioning (HVAC) Control Module - Dual Automatic Temperature Control (DATC)
The DATC system uses the HVAC control module, and it also controls the outputs for rear window defrost and climate controlled seats. For details on the HVAC control module communication, refer to Control System Logic in this service information.
The HVAC control module utilizes a Field-Effect Transistor (FET) protective circuit strategy for its actuator outputs. Output load (current level) is monitored for excessive current (typically short circuits) and is shut down (turns off the voltage or ground provided by the module) when a fault event is detected. A short circuit DTC is stored at the fault event and a cumulative counter is started.
When the demand for the output is no longer present, the module resets the Field-Effect Transistor (FET) circuit protection to allow the circuit to function. The next time the driver requests a circuit to activate that has been shut down by a previous short (Field-Effect Transistor (FET) protection) and the circuit is still shorted, the Field-Effect Transistor (FET) protection shuts off the circuit again and the cumulative counter advances.
When the excessive circuit load occurs often enough, the module shuts down the output until a repair procedure is carried out. The Field-Effect Transistor (FET) protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the Field-Effect Transistor (FET) and the ability of the Field-Effect Transistor (FET) to withstand it. A module lifetime level of fault events is established based upon the durability of the Field-Effect Transistor (FET). If the total tolerance level is determined to be 600 fault events, the 3 predefined levels would be 200, 400 and 600 fault events
When each tolerance level is reached, the short circuit DTC that was stored on the first failure cannot be cleared by a command to clear the Diagnostic Trouble Codes (DTCs). The module does not allow the DTC to be cleared or the circuit to be restored to normal operation until a successful self-test proves that the fault has been repaired. After the self-test has successfully completed (no on-demand Diagnostic Trouble Codes (DTCs) present), DTC U1000:00 and the associated DTC (the DTC related to the shorted circuit) automatically clears and the circuit function returns.
When each level is reached, the DTC associated with the short circuit sets along with DTC U1000:00. These Diagnostic Trouble Codes (DTCs) can be cleared using the module self-test, then the Clear DTC operation on the scan tool. The module never resets the fault event counter to zero and continues to advance the fault event counter as short circuit fault events occur.
If the number of short circuit fault events reach the third level, then Diagnostic Trouble Codes (DTCs) U1000:00 and U3000:49 set along with the associated short circuit DTC. DTC U3000:49 cannot be cleared and a new module must be installed after the repair.
The HVAC control module requires Programmable Module Installation (PMI) when it is replaced.
Ambient Air Quality Sensor (if equipped)
The ambient air quality sensor is an input to the HVAC control module. When pollution and bad odors coming from the external environment are detected, the air inlet door automatically closes.
Ambient Air Temperature (AAT) Sensor
The Ambient Air Temperature (AAT) sensor is an input to the PCM. If the outside air temperature is below approximately 0deg.C (32deg.F), the PCM does not allow the A/C compressor clutch to engage.
The PCM sends raw ambient air temperature data to the HVAC control module. The HVAC control module filters the raw data, sends it to the APIM and the touchscreen displays the outside temperature.
After replacing an Ambient Air Temperature (AAT) sensor, the sensor data must be reset by following the menu prompts on the FDRS scan tool. Refer to: Reset the Outside Air Temperature Sensor Learned Values .
A/C Compressor Clutch Assembly
When battery voltage is applied to the A/C compressor clutch field coil, the clutch disc and hub assembly is drawn toward the A/C clutch pulley. The magnetic force locks the clutch disc and hub assembly and the A/C clutch pulley together as one unit, causing the compressor shaft to rotate with the engine. When battery voltage is removed from the A/C compressor clutch field coil, springs in the clutch disc and hub assembly move the clutch disc away from the A/C clutch pulley.
An A/C clutch diode is integrated into the coil for A/C clutch field coil circuit spike suppression.
Internal Heat Exchanger (IHX)
The evaporator inlet and outlet manifold incorporates the Internal Heat Exchanger (IHX) and is serviced as an assembly. The Internal Heat Exchanger (IHX) combines a section of the A/C suction and liquid refrigerant lines into one component. It uses the cold vapor from the evaporator to cool the hot liquid from the condenser before it enters the Thermostatic Expansion Valve (TXV). After the Thermostatic Expansion Valve (TXV), more liquid refrigerant is available for absorbing heat in the evaporator. The result is an increase in cooling and operating efficiency of the HVAC system.
Externally Controlled Variable Displacement Compressor
Variable displacement compressor internals are similar to fixed displacement compressors. The pistons are placed around an angled plate (swash plate) and are pushed back and forth as the plate rotates. Variable displacement compressors vary the swash plate angle to allow piston displacement to vary from 5% (default) to 100% of full capacity to meet cooling demand.
The externally controlled variable displacement compressor has the following characteristics:
- non-serviceable shaft seal.
- a non-serviceable pressure relief valve installed in the rear of the compressor to protect the refrigerant system against excessively high refrigerant pressures.
- Refer to Specifications in the Climate Control System, General Information, Service Information for the appropriate refrigerant and refrigerant oil. This oil contains special additives required for the A/C compressor. The oil may have some slightly dark-colored streaks while maintaining normal oil viscosity. This is normal for this A/C compressor because of break-in wear that can discolor the oil.
The piston displacement of the externally controlled variable displacement compressor is controlled by a PWM signal from the PCM which electronically drives the control valve. The control valve drives the crankcase pressure and thus the swash plate angle. The externally controlled variable displacement compressor achieves precise cooling capability based on the cabin temperature and driving conditions, resulting in the target evaporator core temperature. The target evaporator core temperature range for the EATC system is 3-8deg.C (37.4-46.4deg.F); 3-5deg.C (37.4-41deg.F) for the EMTC system.
The PCM pulse width modulates the ground to the externally controlled variable displacement compressor control valve to change the displacement of the A/C compressor by changing the swash plate angle based on the following items:
- Ambient air temperature
- Engine RPM
- Evaporator temperature
- High side and low side A/C pressures
- Temperature and mode settings of the climate control head
Thermostatic Expansion Valve (TXV)
The Thermostatic Expansion Valve (TXV) is located at the evaporator core inlet and outlet tubes at the center rear of the engine compartment. The Thermostatic Expansion Valve (TXV) provides a restriction to the flow of refrigerant and separates the low-pressure and high-pressure sides of the refrigerant system. Refrigerant entering and exiting the evaporator core passes through the Thermostatic Expansion Valve (TXV) through 2 separate flow paths. An internal temperature sensing bulb senses the temperature of the refrigerant flowing out of the evaporator core and adjusts an internal pin-type valve to meter the refrigerant flow into the evaporator core. The internal pin-type valve decreases the amount of refrigerant entering the evaporator core at lower temperatures and increases the amount of refrigerant entering the evaporator core at higher temperatures.
A/C Condenser
The A/C condenser is an aluminum fin-and-tube design heat exchanger. It cools compressed refrigerant gas by allowing air to pass over fins and tubes to extract heat, and condenses gas to liquid refrigerant as it is cooled.
Receiver Drier
The receiver drier stores high-pressure liquid and the desiccant bag mounted inside the receiver drier removes any retained moisture from the refrigerant.
The receiver drier is externally mounted to the LH side of the condenser core.
Blower Motor Control Module
The blower motor and the blower motor speed control are combined into one assembly called the blower motor control module. The blower motor pulls air from the air inlet and forces it into the climate control housing and the plenum chamber where it is mixed and distributed. The blower motor speed control uses a PWM signal from the HVAC Control Module to determine the desired blower speed and varies the ground feed for the blower motor to control the speed.
Evaporator Core
The evaporator core is an aluminum tube and fin type and is located in the climate control housing. A mixture of liquid refrigerant and oil enters the evaporator core through the evaporator core inlet tube and continues out of the evaporator core through the evaporator core outlet tube as a vapor. During A/C compressor operation, airflow from the blower motor is cooled and dehumidified as it flows through the evaporator core fins.
Heater Core
The heater core consists of fins and tubes arranged to extract heat from the engine coolant and transfer it to air passing through the heater core.
Climate Control Housing
The climate control housing directs airflow from the blower motor through the evaporator core and heater core. All airflow from the blower motor passes through the evaporator core. The airflow is then directed through or around the heater core by the temperature doors. After passing through the heater core, the airflow is distributed to the selected outlet by the airflow mode doors.
A/C Pressure Transducer
The PCM monitors the discharge pressure measured by the A/C pressure transducer. As the refrigerant pressure changes, the resistance of the A/C pressure transducer changes. It is not necessary to recover the refrigerant before removing the A/C pressure transducer.
A 5-volt reference voltage is supplied to the A/C pressure transducer from the PCM. The A/C pressure transducer receives a ground from the PCM. The A/C pressure transducer then sends a voltage to the PCM to indicate the A/C refrigerant pressure.
In-Vehicle Air Quality Particulate Sensor (if equipped)
The in-vehicle air quality particulate sensor is an input to the HVAC control module. When pollution and bad odors coming from the internal environment are detected, the air inlet door automatically opens.
In-Vehicle Temperature and Humidity Sensor (if equipped)
The in-vehicle temperature and humidity sensor is an input to the HVAC control module. The in-vehicle temperature and humidity sensor contains a thermistor and a sensing element which separately measures the in-vehicle air temperature and the humidity. The HVAC control module may adjust the air inlet door based on the in-vehicle temperature and humidity sensor information to maintain the desired humidity of the passenger cabin air.
Sunload Sensor
The sunload sensor supplies information to the HVAC control module indicating the intensity of the sun on the vehicle. The HVAC control module compensates high sun load with higher blower speed and reduced discharge temperatures.
Air Discharge Temperature Sensors
There are 2 air discharge temperature sensors in the EATC system:
- Driver side footwell air discharge temperature sensor
- Driver side register air discharge temperature sensor
There are 4 air discharge temperature sensors in the DATC system:
- Driver side footwell air discharge temperature sensor
- Driver side register air discharge temperature sensor
- Passenger side footwell air discharge temperature sensor
- Passenger side register air discharge temperature sensor
The air discharge temperature sensors contain a thermistor and are inputs to the HVAC control module. The sensors vary their resistance with the temperature. As the temperature rises, the resistance falls. As the temperature falls, the resistance rises. The HVAC control module uses the sensor information to maintain the desired temperature of the passenger cabin air.
Air Distribution Door Actuator
The air distribution door actuator contains a reversible electric motor and a potentiometer. The potentiometer allows the HVAC control module to monitor the position of the airflow mode door.
Air Inlet Door Actuator
The air inlet door actuator contains a reversible electric motor and a potentiometer. The potentiometer allows the HVAC control module to monitor the position of the airflow mode door. The HVAC control module drives the actuator motor in the direction necessary to move the door to the position set by the recirculation button and when the MAX A/C, Defrost or MAX Defrost buttons are selected.
Temperature Door Actuator
The EATC system has one temperature door actuator located on the passenger side of the climate control housing. The temperature door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC control module to monitor the position of the temperature blend door.
Driver Side Temperature Door Actuator
The DATC system has two temperature door actuators. The temperature door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC control module to monitor the position of the temperature blend door.
Passenger Side Temperature Door Actuator
The DATC system has two temperature door actuators. The temperature door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC control module to monitor the position of the temperature blend door.
Evaporator Temperature Sensor
The evaporator temperature sensor contains a thermistor. Sensor resistance varies with evaporator temperature. As the temperature rises, the resistance falls. As the temperature falls, the resistance rises. The evaporator temperature sensor is an input to the HVAC control module and the information is relayed to the PCM over the HS-CAN. If the temperature is below approximately 2deg.C (35.6deg.F), the PCM does not allow the A/C compressor clutch to engage.
Service Gauge Port Valves
The service gauge port fitting is an integral part of the refrigerant line or component.
- Prior to leak testing, blow air over service gauge port valves to insure an accurate test.
- Special couplings are required for both the high-side and low-side service gauge ports.
- A very small amount of leakage around the Schrader-type valve with the service gauge port valve cap removed is considered normal. Install a new Schrader-type valve core if the seal leaks excessively.
- The A/C service gauge port valve caps are used as primary seals in the refrigerant system to prevent leakage through the Schrader-type valves from reaching the atmosphere. Always install and tighten the A/C service gauge port valve caps to the correct torque after they are removed.
- Follow the procedure and the notes for electronic leak testing. REFER to the appropriate procedure in General Procedures.
| Item | Description | Torque |
|---|---|---|
| 1 | Low-pressure service gauge port valve cap | 0.8 Nm |
| 2 | Low-pressure service gauge port valve O ring | -- |
| 3 | Low-pressure Schrader-type valve | 1.8 Nm |
| 4 | Low-pressure service gauge port valve | -- |
| 5 | High-pressure service gauge port valve | -- |
| 6 | High-pressure Schrader-type valve | 2.5 Nm |
| 7 | High-pressure service gauge port valve O ring | -- |
| 8 | High-pressure service gauge port valve cap | 0.8 Nm |
Refrigerant System Dye
A fluorescent refrigerant system dye wafer is added to the receiver drier desiccant bag at the factory to assist in refrigerant system leak diagnosis. This fluorescent dye wafer dissolves after about 30 minutes of continuous A/C operation. It is not necessary to add additional dye to the refrigerant system before diagnosing leaks, even if a significant amount of refrigerant has been removed from the system. REFER to the appropriate procedure in General Procedures.
Replacement desiccant bags, either separately or part of the receiver drier assembly, are equipped with a new fluorescent dye wafer. It is not necessary to add additional dye to the refrigerant system before diagnosing leaks. If the system has been out of refrigerant through the winter the dye at the leak point may have oxidized and may not fluoresce. If this happens, recharge and operate the A/C system to circulate the oil and allow any residual dye to show up at the leak point. It is important to understand that dye adheres to the oil not the refrigerant; the refrigerant carries the oil out of the leak point.
Electric Booster Heater System
For system operation and component description information on the electric booster heater. Refer to: Supplemental Climate Control - System Operation and Component Description .