Sensors and Controls
Sensors and Controls
The solar sensor is mounted on the top surface of the fascia between the driver's defrost grille and speaker grille.
The sensor is a photo-diode which is calibrated to measure direct sunlight. It provides an output signal to the A/CCM which automatically reduces air temperature and increases fan speed (airflow volume) to compensate for solar heating.
This thermistor device changes electrical resistance as a result of temperature variations. The sensor is positioned next to the evaporator fins and measures air temperature after it has passed through the evaporator. The sensor inputs a signal to the A/CCM which controls the compressor (see table) when the refrigeration system is operating.
The sensor's connector is located on the LH side of the air conditioning unit, in front of the main power connector.
Evaporator Temperature Signal Compressor State
3 °C ON-clutch engaged
2 °C OFF-clutch disengaged
The A/CCM disengages the compressor clutch when the temperature of the air off the evaporator is 2 °C or less. This is to prevent the moisture which may collect between the cooling fins of the evaporator from freezing and thus restricting airflow.
The heater matrix temperature sensor is a thermistor which changes its electrical resistance in response to changes in air temperature converting a temperature rating to an electrical signal.
The sensor connector is located on the RH SIDE of the air conditioning unit. The sensor bead is located inside the unit down-stream from the heater matrix and measures the 'post-heater' air temperature, before the air is distributed to the cabin The sensor provides a signal to the A/CCM which adjusts the duty ratio of the water valve to provide the required air temperature from the heater.
The sensor is a thermistor which changes its electrical resistance in response to changes in air temperature, converting a temperature rating to an electrical signal.
The ambient temperature sensor measures exterior air temperature and is mounted on the RH horn bracket which is located on the front bumper beam.
The signal from the ambient sensor allows the A/CCM to compensate for the ambient conditions and to display the information on the control panel - updated every four (4) seconds.
Sensor response is 'damped' by the A/CCM and therefore does not appear to react to temperature changes as quickly as the other sensors. This feature prevents the effects of sudden changes in air outlet temperatures due to factors such as:
Recirculating air from the engine cooling pack at low vehicle speeds
Sudden changes in ambient temperature
The effects of water splash
Motorised In-car Aspirator:
Cabin air is drawn through a grille (located near the steering column on the knee bolster) over a thermistor. Remotely mounted from the thermistor is the motorized aspirator with a rubber hose which connects both components.
The electrical resistance of the thermistor changes in response to variations in air temperature and converts this temperature rating into an electrical signal; the signal is used by the A/CCM to adjust the temperature, airflow and air distribution from the air conditioning unit.
Coolant Temperature Signal.
This signal is supplied to the A/CCM from the instrument cluster, the input being required to:
Provide blower inhibit control to avoid the system in heating mode delivering cold air when the coolant temperature is below 35C unless DEFROST is selected.
To progressively increase the fan speed up to maximum blower speed during warm up control.
To assist in the control of the outlet temperature.
To avoid possible pump or valve damage caused by ice particles in the coolant.
Compressor ON Signal.
This signal monitors the compressor relay to confirm the compressor operating state and so provide relevant fault information.
Servo Motor Control.
Flap position, which directs the flow of air through the system, is controlled by servo motors; these may be driven in either a clockwise or anti-clockwise direction by signals from the A/CCM. Motor, thus flap position, is monitored via a feedback potentiometer which is situated within the motor housing.
Servo motors control the following flaps:
RH and LH Air Intake (Fresh/Recirc)
Center Vent
Defrost
Foot
Cool Air Bypass
Blower Motor Control.
The A/CCM controls the speed of two blower motors which deliver airflow to the air conditioning unit. The blower motors are regulated by power transistor modules which provide a linear variation of blower speed.
Relationship Manual Control Blower Speed/Voltage
NOTE: Blower motors are inhibited when the engine coolant temperature is below 35C and heating is demanded, unless DEFROST is selected.
