Part 1
Control Components
COMPONENT LOCATION
OVERVIEW
The A/C (air conditioning) control system automatically adjusts the temperature, volume and distribution of the air from the heater to maintain the individual temperature levels selected for the LH (left-hand) and RH (right-hand) sides of the cabin. The system also has manual overrides for the intake air source, blower speed and air distribution.
Some vehicles may be fitted with a 4 zone climate control system.
ATC MODULE
The ATC (automatic temperature control) module is installed in the center of the instrument panel. An integral control panel contains push switches and rotary switches/knobs for system control inputs. Orange tell-tale LED (light emitting diode) s in the switches and switch surrounds illuminate to indicate the current settings of the system. The rotary temperature switch is graduated in degrees Celsius, except on USA vehicles, where it is graduated in degrees Fahrenheit.
An in-vehicle temperature sensor and associated electric fan are installed behind a grille in the control panel.
The ATC (automatic temperature control) module processes inputs from the control panel switches and system sensors, then outputs the appropriate signals to control the A/C (air conditioning) system. In addition to controlling the A/C (air conditioning) system, the ATC (automatic temperature control) module also controls the following:
- The heated windshield and windshield wiper parking area heater (optional fit, not available on vehicles with infra red protection glass).
- The windshield washer jet heaters.
- The heated rear window.
- The front seat heaters.
NOTE: Operation of the climatic seats is controlled by software in the center switch pack, not the ATC (automatic temperature control) module.
Control Panel
The switches on the control panel have the following functions:
Heated Windshield Switch
Energizes the heated windshield and the windshield wiper parking area heater for a set time period, until the switch is pressed again or until the engine stops, whichever occurs first. A LED (light emitting diode) above the switch is illuminated while the heaters are on.
LH and RH Seat Heater Switches
Activates the heater elements in the seat cushion and seat back at one of two heat levels. The first press of the switch energizes the heater elements at the higher heat setting and illuminates two LED (light emitting diode) s in the switch. A second press of the switch sets the heater elements to the lower heat setting and extinguishes one of the LED (light emitting diode) s. A further press of the switch de-energizes the heater elements and extinguishes the second LED (light emitting diode). The seat heaters remain on until selected off or the ignition is switched off.
NOTE: Operation of the climatic seats is controlled by software in the center switch pack, not the ATC (automatic temperature control) module.
LH and RH Temperature Switches
Adjusts the nominal temperature settings of the LH (left-hand) and RH (right-hand) sides of the cabin between 16 and 28 degrees C (60 and 84 degrees F). The temperature range is engraved on the switch surrounds. A pointer on each switch indicates the selected temperature. In the minimum and maximum temperature positions, the system operates at maximum cooling or maximum heating respectively.
Automatic Mode Switch
Activates the automatic modes for air volume and distribution and also activates the A/C (air conditioning) compressor. Separate LED (light emitting diode) s in the automatic mode switch illuminate when the blower and the distribution control doors are in automatic mode. Manually selecting the blower speed or a distribution switch extinguishes the related LED (light emitting diode).
Blower Switch
For manual adjustment of blower speed. Up to seven LED (light emitting diode) s in the switch surround illuminate to indicate the selected blower speed.
A/C Switch
Controls activation of the A/C (air conditioning) compressor. Allows the A/C (air conditioning) compressor to be selected off for economy operation. A LED (light emitting diode) above the switch is illuminated when the A/C (air conditioning) compressor is selected on.
Recirculation Switch
For manual or automatic selection of fresh or recirculated air. Two LED (light emitting diode) s above the switch illuminate to indicate the mode and position of the recirculation doors. The first press of the switch sets the recirculation doors to automatic mode and illuminates the LH (left-hand) LED (light emitting diode). A second press of the switch manually sets the recirculation doors to the recirculation position, extinguishes the LH (left-hand) LED (light emitting diode) and illuminates the RH (right-hand) LED (light emitting diode). A further press of the switch manually sets the recirculation doors to the fresh air position and extinguishes the RH (right-hand) LED (light emitting diode).
Maximum A/C Switch
For selection of maximum A/C (air conditioning) when the ignition is on or rest heating when the ignition is off. A LED light emitting diode) above the switch is illuminated when maximum cooling or rest heating is selected.
Distribution Switches (Windshield, Face and Footwell)
For manual selection of air distribution in any combination of windshield, face and footwell outlets. A LED (light emitting diode) above each switch illuminates when a selection is made.
Defrost Program Switch
Activates a program that automatically selects the heated windshield on, activates the A/C (air conditioning) compressor and changes the system settings to direct dry heat to the windshield. A LED (light emitting diode) above the switch is illuminated while the defrost program is active.
Heated Rear Window Switch
Enabled only with the engine running. Pressing the switch energizes the heated rear window for a set time period, until the switch is pressed again or until the engine stops, whichever occurs first. A LED (light emitting diode) above the switch is illuminated while the heater is on.
Inputs and Outputs
Five electrical connectors provide the interface between the ATC (automatic temperature control) module and the vehicle/heater assembly wiring.
The system receives ambient temperature, engine coolant temperature, engine speed and vehicle speed inputs in K bus messages from the instrument cluster. If the K bus messages are missing or faulty, the ATC (automatic temperature control) module adopts the following default values:
- Ambient temperature = 0 degrees C (32 degrees F).
- Engine coolant temperature = 80 degrees C (176 degrees F).
- Engine speed = 800 rev/min.
- Vehicle speed = zero.
If a fault develops in the input from the temperature selector switch on the control panel, the ATC (automatic temperature control) module adopts a default value of 22 degrees C (72 degrees F).
IN-VEHICLE TEMPERATURE SENSOR
The in-vehicle temperature sensor is an encapsulated NTC (negative temperature coefficient) thermistor that provides the ATC (automatic temperature control) module with an input of cabin air temperature. The in-vehicle temperature sensor is installed behind a grille in the ATC (automatic temperature control) module control panel. An electric fan in the ATC (automatic temperature control) module runs continuously, while the ignition is on, to draw air through the grille and across the in-vehicle temperature sensor.
The ATC (automatic temperature control) module uses the signal from the in-vehicle temperature sensor for control of the coolant temperature valve(s), blower speed and air distribution.
The signal voltage from the in-vehicle temperature sensor is between 0 and 5 V. The ATC (automatic temperature control) module monitors the signal voltage and defaults to a temperature of 20 degrees C (68 degrees F) if it goes out of the range 0.573 - 4.882 V:
- If the signal voltage is less than 0.573 V, the ATC (automatic temperature control) module assumes there is a short circuit to ground.
- If the signal voltage is more than 4.882 V, the ATC (automatic temperature control) module assumes there is an open circuit or a short circuit to battery.
REFRIGERANT PRESSURE SENSOR
The refrigerant pressure sensor provides the ATC (automatic temperature control) module with a pressure input from the high pressure side of the refrigerant system. The refrigerant pressure sensor is located in the refrigerant line between the condenser and the thermostatic expansion valve.
The ATC (automatic temperature control) module supplies a 5 V reference voltage to the refrigerant pressure sensor and receives a return signal voltage, between 0 and 5 V, related to system pressure.
The ATC (automatic temperature control) module uses the signal from the refrigerant pressure sensor to protect the system from extremes of pressure and to calculate A/C (air conditioning) compressor load on the engine for idle speed control. The ATC (automatic temperature control) module also provides a cooling fan request signal over the K bus to the instrument cluster. The cluster outputs this request to the ECM (engine control module) over the high speed CAN (controller area network) bus.
To protect the system from extremes of pressure, the ATC (automatic temperature control) module disengages the A/C (air conditioning) compressor clutch if the pressure:
- Decreases to 1.9 ± 0.2 bar (27.5 ± 3 lbf/in2): the ATC (automatic temperature control) module engages the A/C (air conditioning) compressor clutch again when pressure increases to 2.8 ± 0.2 bar (40.5 ± 3 lbf/in2 ).
- Increases to 33 ± 1 bar (479 ± 14.5 lbf/in2): the ATC (automatic temperature control) module engages the A/C (air conditioning) compressor clutch again when pressure decreases to 23.5 ± 1 bar (341 ± 14.5 lbf/in2).
EVAPORATOR TEMPERATURE SENSOR
The evaporator temperature sensor is a NTC (negative temperature coefficient) thermistor that provides the ATC (automatic temperature control) module with a temperature signal from the air outlet side of the evaporator. The evaporator temperature sensor is installed in the RH side of the heater assembly casing, and extends into the core of the evaporator.
The ATC (automatic temperature control) module uses the input from the evaporator temperature sensor to control the engagement and disengagement of the A/C (air conditioning) compressor clutch, to prevent the formation of ice on the evaporator.
The signal voltage from the evaporator temperature sensor is between 0 and 5 V. The ATC (automatic temperature control) module monitors the signal voltage and defaults to a temperature of 0 degrees C (32 degrees F) if it goes out of the range 0.157 - 4.784 V:
- If the signal voltage is less than 0.573 V, the ATC (automatic temperature control) module assumes there is a short circuit to ground.
- If the signal voltage is more than 4.882 V, the ATC (automatic temperature control) module assumes there is an open circuit or a short circuit to battery.
HEATER TEMPERATURE SENSOR
The heater temperature sensor is a NTC (negative temperature coefficient) thermistor that provides the ATC (automatic temperature control) module with a temperature signal from the air outlet side of the heater core. Two sensors are installed, one each side of the vehicle center-line.
The ATC (automatic temperature control) module uses the input from the heater temperature sensors to control the operation of the coolant valves.
The signal voltage from each heater temperature sensor is between 0 and 5 V. The ATC (automatic temperature control) module monitors the signal voltage and defaults to a temperature of 55 degrees C (131 degrees F) if it goes out of the range 0.173 - 4.890 V:
- If the signal voltage is less than 0.173 V, the ATC (automatic temperature control) module assumes there is a short circuit to ground
- If the signal voltage is more than 4.890 V, the ATC (automatic temperature control) module assumes there is an open circuit or a short circuit to battery.
AUXILIARY COOLANT PUMP
The auxiliary coolant pump is an electric pump that ensures there is a satisfactory flow rate through the heater core at low engine speeds. The auxiliary coolant pump is installed in the engine compartment, in a rubber mounting attached to the side of the LH (left-hand) suspension turret. Operation of the auxiliary coolant pump is controlled by a power supply from the ATC (automatic temperature control) module.
COOLANT VALVES
The coolant valves control the coolant flow to each side of the heater core. The coolant valves are installed in the engine compartment on a bracket attached to the side of the LH (left-hand) suspension turret.
Each coolant valve is a normally open solenoid valve controlled by a PWM (pulse width modulation) signal from the ATC (automatic temperature control) module. The ATC (automatic temperature control) module changes the length of time the coolant valve is open each duty cycle between 0 second (valve closed) and 3.6 seconds (valve held open). On the automatic system, the PWM (pulse width modulation) signals to the two valves are phase offset by 1.8 seconds to reduce coolant flow fluctuations.
SUNLIGHT SENSOR
The sunlight sensor consists of two photoelectric cells that provide the ATC (automatic temperature control) module with inputs of light intensity, one as sensed coming from the left of the vehicle and one as sensed coming from the right. The inputs are a measure of the solar heating effect on vehicle occupants and used by the ATC (automatic temperature control) module to adjust blower speed, temperature and distribution to improve comfort. The sensor is installed in the center of the fascia upper surface.
If one of the photoelectric cells is faulty, the output from the other photoelectric cell is used for both sides of the vehicle. If both photoelectric cells are faulty, the ATC (automatic temperature control) module uses a default value of zero.
POLLUTION SENSOR
The pollution sensor allows the ATC (automatic temperature control) module to monitor the ambient air for the level of carbon monoxide (CO) and oxides of nitrogen (NOx). The pollution sensor is installed at the rear of the radiator, on the upper left side of the fan cowl.
The ATC (automatic temperature control) module outputs a battery power supply to heat the pollution sensor to operating temperature, and a 5 V reference voltage for the signal. The signal voltage from the pollution sensor is between 0 and 5 V.
If there is a fault with the pollution sensor, the ATC (automatic temperature control) module disables automatic closing of the recirculation doors on detection of pollutants.