Heating, Ventilation, Air Conditioning (HVAC)
The Heating, Ventilation, Air Conditioning (HVAC) system is divided into two sub-systems:
These two sub-systems share many components. This section contains information on all the components that are shared by both systems. The cabin system components are located at the front of the vehicle and the battery system components are located at the rear of the vehicle.
The controls for the HVAC system are mounted on the center console and are connected to the center console harness.
The 12V controller is the main Electronic Control Unit (ECU) for the HVAC system. It is fitted at the front of the center console on the RH side and connects to the front harness using two connectors.
Vehicle Management System (VMS)
The VMS is located in the passenger footwell. Its purpose is to monitor the battery temperature. Battery cooling takes priority over cabin temperature and, if necessary, the VMS will instruct the 12V controller to divert cooling from the cabin.
The switchpack is located under the LH side of the dash and receives input directly from switches. It provides a signal to the 12V controller denoting key ON/OFF. It also communicates its status to the VMS via the Controller Area Network (CAN) bus and switches power to the fan control module and seat heaters.
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WARNING: The battery can generate up to 420V, with a high current. Extreme care should be taken when working on high voltage systems. When removing or replacing the 400V controller, always ensure the key is removed from the ignition switch and that the Auxiliary Power Supply (APS) is inhibited. |
LH side
RH side
The 400V controller is a non-serviceable unit located under the hood and contains two Printed Circuit Boards (PCB). One PCB controls the operation of the PTC heater and the and the other controls the compressor. Aluminum cooling fins help to dissipate heat generated within the assembly.
The compressor is mounted under the hood below the HVAC assembly. The compressor is a non-serviceable 100V to 420V Direct Current (DC) rotary/rolling piston type pump with a maximum rotational speed of 6500 RPM.
The compressor contains PolyVinylEther (PVE) lubrication oil. This has greater electrical insulating properties than the conventional Polyalkylene Glycol (PAG) Air Conditioning (A/C) lubrication oil. It is important that the compressor is kept upright at all times to retain this oil in the compressor sump.
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WARNING: Due to the high voltage, the connector cap should not be removed. |
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CAUTION: Use of the incorrect oil may affect the dielectric strength of the motor and potentially cause an internal short circuit as well potentially affecting the bearing life. |
The condenser is mounted under the hood and is attached by two bolts and two studs with nuts. The condenser is constructed from aluminum alloy with alloy fins to increase the surface area, thus increasing the rate at which heat is transferred to the surrounding air.
Two pipes connect the condenser to the rest of the HVAC system. The upper pipe has an adapter, which forms a male union connecting the condenser to the pipe from the compressor. The lower pipe also has a male union connecting the condenser to the pipe from the receiver drier.
Two ten blade plastic cooling fans are mounted, in plastic housings, on the condenser. The fan motors have separate connectors, which connect to the fan control module. The two fan housings are attached to the condenser by screws and nuts. Each fan motor is attached to the fan housing by self-tapping screws.
Fan rotation is marked on the fans and the motor connections are pre-wired to a non-reversible connector to avoid incorrect fan rotation due to accidentally reversed polarity.
The fan control module is located on the RH inner wing under the hood. The fan control module contains three relays which switch the power to the condenser cooling fans.
The evaporator is mounted within the HVAC assembly with the inlet and outlet pipes protruding through the RH side casing to provide a fixing point for the TXV. Fins around the evaporator coils increases the area of the cooling surfaces and improves efficiency. Foam padding protects the unit from vibration and provides an effective fitment within the HVAC assembly casing.
Thermostatic Switch (Froststat)
The sensor is mounted on the outer RH side of the HVAC assembly, with the probe protruding into the fins of the evaporator.
Thermal Expansion Valves (TXV)
Two TXVs are fitted in the HVAC system, both are identical and they operate in the same way. One is fitted to the inlet and outlet pipes of the HVAC evaporator and the other to the inlet of the battery heat exchanger.
The receiver drier is a non-serviceable unit located below and to the right of the 400V controller, and it filters, stores and dries the refrigerant leaving the condenser. The filter consists of a particulate sieve and also a molecular filter. A blocked filter would prevent HVAC cooling of the battery heat exchanger which could disable the vehicle, as well as preventing cabin cooling. The receiver drier must be replaced whenever an HVAC system leak has been detected and repaired, to prevent contamination. A sight glass is provided in the top of the assembly to aid in the diagnosis of some types of A/C faults. For further information, refer to this information. .
Correct operation of the unit depends on the correct direction of flow and the top of the unit is marked IN, below which the clamp should be orientated as shown in the illustration.
The high pressure charge port is located under the hood on the RH side. This pipe directs the high pressure refrigerant gas from the compressor to the condenser. A Schraeder valve forms a port in the pipe which allows the connection of charging/discharging equipment for servicing purposes. The connection is a 16 mm quick coupler. The valve is fitted with a screw-on cap to prevent refrigerant leaking through the valve and also to prevent the ingress of dirt.
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CAUTION: Keep the port capped at all times to prevent contamination. |
The low pressure charge port is located under the hood between the 400V controller and the bulkhead. This pipe forms a spur in the pipes leading back to the compressor. A Schraeder valve forms a port in the pipe which allows the connection of charging/discharging equipment for servicing purposes. The connection is a 13 mm quick coupler. The valve is fitted with a screw-on cap to prevent refrigerant leaking through the valve and also to prevent the ingress of dirt.
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CAUTION: Keep the port capped at all times to prevent contamination. |
The A/C pressure transducer is fitted in the pipe between the receiver drier and the battery refrigerant solenoid valve. The transducer body contains a steel diaphragm which measures the pressure in the pipes between the compressor and the two TXVs and compares it against atmospheric pressure.
Each valve has an arrow cast into the assembly body which denotes the direction of refrigerant flow. Although their mounting brackets are different, the valves are internally identical.
The cabin solenoid valve is located in the pipe to the evaporator under the hood to the RH side of the 400V controller.
The battery solenoid valve is located in the pipe to battery heat exchanger behind the RH side of the dash.
Aluminum refrigerant lines connect the system components together with O-rings fitted between the connections to ensure a secure seal. To maintain similar flow velocities around the system, the diameter of the refrigerant lines varies to suit the two pressure/temperature regimes. The larger diameters are installed in the low pressure/temperature regime and the smaller diameters are installed in the high pressure/temperature regime with charge ports incorporated into the refrigerant lines for system servicing.
The HVAC assembly is located under the hood and houses both the evaporator and the PTC heater. A drain is fitted to the bottom of the assembly to remove any condensation.
The assembly contains a flap, which diverts air flow either to bypass or to pass through the PTC heater. The flap actuator is mounted on the front of the assembly.
The thermostatic switch (Froststat) is located on the RH side of the assembly, with a probe that extends into the housing and through to the evaporator. A single electrical connector connects the inlet and outlet temperature sensors to the front harness.
The blower is a centrifugal fan with intakes at either end. It is clipped to the LH side of the HVAC assembly.
Positive Temperature Coefficient (PTC) Heater
Heating is provided by the PTC heater. The heater consists of five heating elements and is mounted below the outlet from the HVAC assembly. It is a self-regulating, semi-conductor heater dependant on airflow and air temperature.
Intake/Outlet Temperature Sensors
The outlet air temperature sensor is located on top of the HVAC assembly. The intake air temperature sensor is located at the front of the HVAC assembly by the evaporator. The intake and outlet temperature sensors are connected to the vehicle harness via the same connector.
Both sensors are Negative Temperature Coefficient (NTC) thermistors with a resistance of 10kΩ at 77°F (25ºC). As temperature increases, the resistance drops. The 12V controller can calculate the temperature from the measured value.
Ambient Air Temperature Sensor
This sensor is a two wire NTC thermistor, which is mounted under the hood alongside the LH headlight and connected to the front harness.
The air distribution unit is a plastic assembly mounted between the hood compartment and the cabin, below the windshield, and is connected to the HVAC assembly by a short length of large diameter, flexible hose.
The fresh air unit is located under the hood on the vehicle body behind the HVAC assembly with two intakes directing fresh air to the cabin.
The Heating Ventilation, Air Conditioning (HVAC) system controls the temperature, humidity, distribution and quality of air within the cabin, in order to achieve and maintain the conditions demanded by the vehicle occupants.
Air enters the vehicle through two mesh grilles at the front of the vehicle and passes to a blower under the hood through the fresh air unit.
Approximately 10% of the air entering the fan is drawn from within the cabin via vents in the footwells allowing warm or cool air from the cabin to be reused. This reduces the energy needed to bring the air entering the vehicle to the desired temperature.
Air from the fan is forced into the HVAC assembly where it is heated and/or cooled, according to the control settings.
Panel illumination is provided by an electroluminescent panel onto which the switches, knobs and indicator lamps are mounted. This panel operates at a very low Alternating Current (AC) provided by an inverter mounted underneath the control panel.
LEDs illuminate when seat heaters, Air Conditioning (A/C), heating or recirculation are active.
Air enters the air distribution unit from the flexible hose in the hood compartment area and depending on the position of the air distribution flap air flow is directed through ducts to either the windshield, face/dash level or foot level vents. The face level vents can be adjusted to direct air flow.
The direction of air entering the cabin can be controlled using the rotary air distribution knob, which operates a potentiometer in the driver’s control panel. The 12V controller monitors the position of the potentiometer and provides power to the mode actuator. The mode actuator is a worm-type actuator on the RH side of the unit moves the air distribution flaps, via a lever mechanism, to distribute the air as required.
The actuator moves the air distribution flap based on the resistance of the potentiometer.
If the control knob is turned to a point between two selections, air delivery will be shared between those two air outlets. The flaps will remain in the last used position until redirected.
To avoid fumes being drawn into the vehicle, the fresh air unit can be set to recirculate air from the cabin rather than draw in air from outside. Recirculation can be switched ON/OFF by pressing the recirculation button on the control panel. When on, a green LED will be illuminated.
At an ambient temperature of 77°F (25°C) the heating and cooling systems are designed to provide the following performance:
| Fan Speed | |||
| Low | Medium | High | |
| Cabin Heating | |||
| Temperature after 4 mins °F (°C) | 118 (48) | 122 (50) | 129 (54) |
| Cabin Cooling | |||
| Temperature after 4 mins °F (°C) | 55 (13) | 55 (13) | 55 (13) |
Load shedding disables the functionality of some non-critical features of the vehicle for short periods of time, if the battery is under heavy load or in a hot climate. For example, if the ABS pump is operational, it can draw up to 60A from the battery. In this situation, load shedding parameters include:
When load shedding takes place, the controls will not indicate this is happening. The heated seats/electric window switches remain illuminated even if the VMS has temporarily disabled them. Once load shedding is no longer required, full functionality will automatically resume.
Air Conditioning (A/C) Refrigerant System
The refrigerant system transfers heat from the vehicle interior to the outside atmosphere to provide the HVAC assembly with dehumidified cool air. The system comprises a compressor, condenser, Thermal Expansion Valve (TXV) and an evaporator connected by refrigerant lines. The system is a sealed, closed loop system filled with a charge weight of R134a refrigerant as the heat transfer medium. Oil is added to the refrigerant to lubricate the internal components of the compressor.
To accomplish the transfer of heat, the refrigerant is circulated around the system where it passes through two pressure/temperature regimes. In each of the pressure/temperature regimes, the refrigerant changes state. During the state changes, maximum heat absorption or release occurs.
The low pressure/temperature regime is from the TXV, through the evaporator to the compressor. The refrigerant decreases in pressure and temperature at the TXV, then changes state from liquid to vapour in the evaporator in order to absorb heat.
The high pressure/temperature regime is from the compressor, through the condenser to the TXV. The refrigerant increases in pressure and temperature as it passes through the compressor, then releases heat and changes state from vapour to liquid in the condenser.
The 12V controller transmits signals to the 400V controller, based on control settings and VMS requests, to control the desired level of heating or cooling. It communicates with the VMS via the CAN bus and also monitors faults.
The 12V controller receives the following inputs:
It monitors the following sensors:
The signal from the ambient air temperature sensor is monitored by the 12V controller in combination with the signal from the pressure transducer. If the refrigerant pressure is higher than expected for a given temperature, the 12V controller will calculate that the refrigerant is hot and will start the condenser cooling fans. Even if the key is removed from the ignition switch, the fans may continue to run for up to one minute.
The 400V controller assembly controls the high voltage HVAC systems based on signals from the 12V controller.
The controlled systems include:
The main purpose of the 400V controller is to isolate the low and high voltage circuits in the vehicle, whilst still allowing monitoring and control of the various HVAC circuits.
Heating and cooling demands made by the user and/or battery will demand varying amounts of power from the 400V controller. Temperature difference (between the user requirement and ambient air) and the rate of air flow through the HVAC assembly will create power drains of between 200W and 2500W for the PTC heater and up to 2500W for the HVAC compressor.
A red LED next to the high voltage IN connector, indicates power. However, if for any reason the battery is disconnected from the controller, a dangerously high voltage could still be present within the unit due to its capacitance. To prevent possible accidents or damage to the vehicle, a circuit within the controller electronics, fed by a 12V +/- 1V connection from the switchpack, detects disconnection and connects the PTC heater to safely discharge the unit. The red LED will remain illuminated until the stored voltage naturally decays below 50V, this may take up to 1 minute.
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WARNING: This safety feature will not operate effectively if the PTC heater is already disconnected. |
The compressor circulates the refrigerant around the system by compressing low pressure, low temperature vapor from the evaporator and discharging the resultant high pressure, high temperature vapor to the condenser.
The compressor operates on 400V, 20-80% PWM up to a maximum current of 8A. Liquid refrigerant cannot be allowed to enter the compressor and is captured in the accumulator mounted on the side of the compressor body, from where it gradually evaporates. The returning gaseous refrigerant is drawn into the compressor through a non-serviceable filter.
The 400V controller provides power to the A/C compressor to compress the gas and force it through to the condenser. The amount of power provided by the 400V controller determines the compressor speed.
NOTE: The compressor is shut off by the 12V controller at pressures greater than 406 psi (28 bar).
The condenser transfers heat from the refrigerant to the surrounding air to convert the vapour from the compressor into a liquid.
As heat is lost from the gaseous refrigerant, droplets form within the gas. These condense on the inner surfaces of the condenser forming liquid refrigerant, which passes out of the condenser on the way to the receiver drier.
During normal driving the refrigerant can dissipate heat to the air being forced through it by the movement of the vehicle. If the vehicle is stationary, or in circumstances where a higher rate of heat transference is required, cooling fans are activated to increase the rate of cooling.
The two condenser fans always operate together. They are switched on when the HVAC 12V controller determines that air flow through the condenser is not adequately cooling the refrigerant to allow it to change from gas to liquid.
| Speed | System Pressure |
| Low Speed | Greater than 116 psi (8 bar) and less than 218 psi (15 bar) |
| High Speed | Greater than 218 psi (15 bar) |
The relays are controlled by the 12V controller to run the fans in parallel (fast speed), in series (slow speed) or to be OFF. This configuration ensures cooling of the condenser occurs evenly over its surface area.
The fans are controlled by three relays (1, 2 and 3) in the fan control module, and draws 7.6A at 13.5V.
NOTE: Relay 4 in the fan control module is redundant.
The evaporator is installed in the air inlet of the heater assembly and absorbs heat from the exterior or recirculated inlet air. Low pressure, low temperature refrigerant changes from liquid to vapour in the evaporator, absorbing large quantities of heat as it changes state.
In A/C mode the flap in the HVAC assembly opens to divert a percentage of the air flow directly to the fresh air unit, bypassing the PTC heater. As the air cools, any moisture in the air condenses, drying the air. Excess moisture collects in the bottom of the HVAC assembly and is drained through a pipe under the vehicle.
Thermostatic Switch (Froststat)
This thermostatic switch (Froststat) is an automatic switch, which causes the cabin refrigerant solenoid to cut out if there is a risk of over cooling, which could cause icing of the evaporator. If there is no demand for battery cooling the compressor is then also shut down.
Thermal Expansion Valves (TXV)
The TXV meters the flow of refrigerant into the evaporator to match the refrigerant flow with the heat load of the air passing through the evaporator matrix.
The valve consists of an aluminum housing containing inlet and outlet passages. A ball and spring metering valve is installed in the inlet passage. The metering valve is controlled by a temperature sensitive tube connected to a diaphragm. The top of the diaphragm senses evaporator outlet pressure and the tube senses evaporator outlet temperature.
Liquid refrigerant flows through the metering valve into the evaporator. The restriction across the metering valve reduces the pressure and temperature of the refrigerant. The restriction also changes the stream of refrigerant into a fine spray, to improve the evaporation process. As the refrigerant passes through the evaporator, it absorbs heat from the air flowing through the evaporator matrix. The increase in temperature causes the refrigerant to vaporize and increase in pressure.
The temperature and pressure of the refrigerant leaving the evaporator act on the diaphragm and temperature sensitive tube, which move to regulate the metering valve opening and so control the volume of refrigerant flowing through the evaporator. The warmer the air flowing through the evaporator matrix, the more heat available to evaporate refrigerant and thus the greater the volume of refrigerant allowed through the metering valve.
The receiver drier acts as a temporary storage area for the refrigerant although its main function is to remove moisture and contaminants from the refrigerant, it provides a reservoir of liquid refrigerant to accommodate changes of heat load at the evaporator. The refrigerant is extremely hygroscopic meaning that it absorbs moisture easily. Without the receiver drier, moisture contained in the refrigerant would form ice in the TXV restricting the flow of the refrigerant to the evaporator.
Moisture is removed by passing the refrigerant though desiccant which removes the moisture. The filtered refrigerant is then passed onto the evaporator.
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WARNING: Servicing must only be carried out by personnel familiar with both the vehicle system and the charging and testing equipment. All operations must be carried out in a well-ventilated area away from open flame and heat sources. |
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WARNING: R134a is a hazardous liquid and if handled incorrectly can cause serious injury. Suitable protective clothing, consisting of face protection, heat-proof gloves, rubber boots and apron or waterproof overalls, must be worn when carrying out operations on the air conditioning system. |
NOTE: Always locate and repair the source of a refrigerant leak before recharging the system.
The refrigerant charge ports are used to recover and recharge the A/C refrigerant from the system using a refrigerant charging station. Refer to the Service Manual for the A/C Refrigerant Recovery and Recharge procedure.
Air Conditioning (A/C) Pressure Transducer
The A/C pressure transducer compares the pressure within the refrigerant system with ambient atmospheric pressure. The transducer receives a 5V feed from the 12V controller and returns a voltage of between 0V and 5V. 0V indicates no difference between atmospheric and pipe pressure, whereas 5V signals a pipe pressure of approximately 508 psi (35 bar). The progression is linear so 2.5V would indicate a pipe pressure of around 247 psi to 261 psi (17 bar to 18 bar). The 12V controller uses the transducer signal to operate the condenser cooling fans and the compressor.
When closed, the valves isolate their corresponding cooling circuits from the rest of the system. Opening the solenoids will divert refrigerant through the evaporator to provide cabin cooling, and/or through the battery heat exchanger to provide additional cooling for the battery.
Both are operated by a Pulse Width Modulated (PWM) signal from the 12V controller and both are either open or closed. The voltage required to open the valves initially can be decreased using approximately 70% PWM modulation to reduce heating of the solenoid coils. Once open, the PWM signal to a solenoid is effectively around 8V.
When there is a very high demand for battery cooling, cabin cooling may be completely suspended until acceptable temperatures are reached in the battery. Similarly, over cooling of the battery will be prevented by the 12V controller switching off the flow of refrigerant through the battery heat exchanger.
Air is drawn from the fresh air unit, unless recirculation has been requested, and from the cabin via the recirculation plenum assembly and is directed through a port in the center of the casing into the HVAC assembly.
Positive Temperature Coefficient (PTC) Heater
In heating mode, the flap in the HVAC assembly closes to force all the air from the HVAC blower over the PTC heating elements where it is heated and then passes through the air distribution unit into the cabin area. The PTC heater will not operate unless the blower is activated. If an excessive outlet air temperature is detected, heating will be suspended although the blower will keep running at low speed.
The heating elements are powered by a PWM signal from the 400V controller in response to signals from the HVAC 12 V controller. The heater requires no other control as it self regulates according to resistance. If the system determines that heating is excessive, PWM is reduced to maintain heating within acceptable limits. This type of heater will reduce heat output automatically from a maximum of around 2.5kW to around 200W if the air temperature is too high or if the airflow is too low.
Intake/Outlet Temperature Sensor
The outlet temperature values are used to monitor the temperature of the conditioned air and to determine the PWM signal to the PTC heater and the compressor. If the sensor signals that air temperature leaving the HVAC assembly is above pre-determined limits the 12V controller will suspend PTC heating.
Ambient Air Temperature Sensor
The ambient air temperature sensor notifies the VMS of the ambient air temperature. The sensor has a resistance of approximately 10kΩ at 68ºF (20ºC). which decreases as temperature increases. This signal is sent to the 12V controller and then to the VMS to be displayed on the touch screen as an indication of the outside temperature.
High Voltage Interlock Loop (HVIL)
The HVIL is a monitoring system embedded in the HVAC system used to monitor the HVAC high voltage circuit. The system is designed to shut down the high voltage electrical systems if the HVIL is broken in the event of a collision or not allow the high voltage battery contactors to close if the loop is opened. If the HVIL is broken, high voltage is immediately removed from the high voltage components and the system is discharged.
The HVIL can be also be broken if the following conditions occur:
NOTE: It may not always be obvious when the HVIL is broken. A blown fuse in the battery to HVAC 400V controller will not be detected by the Vehicle Management System (VMS) or any other module.
If the HVIL is broken and the 400V controller is not receiving voltage, the following conditions will occur:
In addition, if the connection between the 12V controller and the 400V controller is broken, the following conditions will occur:
If the 12V controller is not receiving voltage, the following conditions will occur:
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CAUTION: Failure to accurately diagnose and rectify faults may reduce the working life of components. |
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CAUTION: Correct operation of the cooling system is essential to maintain acceptable battery temperatures. |
The receiver drier has a sight glass for checking the condition of the fluid. Normally, the fluid is clear; the following table shows possible causes for changes to the fluid:
| Symptom | Possible Cause |
| Fluid appears streaky | Excessive oil and/or lack of refrigerant |
| Fluid appears cloudy | Desiccant from the drier has broken down and is circulating with the fluid |
| Fluid contains bubbles | Low in refrigerant and/or air in the system |
The 12V controller is capable of sharing fault data and operating parameters of the HVAC system on the CAN bus or directly through the diagnostic socket. The 20 most recent fault codes are retained in the 12V controller until it receives a reset command from the VMS.
The diagnostic mode can be accessed using a diagnostic tool, which allows direct control of the operation of the following components for fault finding purposes:
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WARNING: Failure to follow the correct procedures can result in serious personal injury. |
HVAC Service Mode must be initiated before evacuation and recharge procedures are carried out. Refer to the General Information section in the Service Manual for initiation of the Service Mode. Service Mode opens both solenoids for complete evacuation, servicing and proper recharge of the system.
Checking the HVAC system pressures will help to diagnose faults. The system can be tested upto the maximum capacity of 30 bar (435 psi) using oxygen free nitrogen: the compressor should shut down at 28 bar (406 psi).