LR3/Disco 3
The sunlight sensor consists of two photoelectric cells that provide the ATCM 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 are used by the ATCM to adjust blower speed, temperature and distribution to
improve comfort. The sensor is installed in the center of the fascia upper surface and is powered by a 5V feed from the
ATCM.
POLLUTION SENSOR
The pollution sensor allows the ATCM to monitor the ambient air for the level of hydrocarbons and oxidized gases such
as nitrous oxides, sulphur oxides and carbon monoxide. The sensor is attached to a bracket on the front-end carrier, at
the top left corner of the condenser.
The pollution sensor is powered by a battery voltage feed from the ATCM, and returns separate signals of hydrocarbon
and oxidized gases.
If there is a fault with the pollution sensor, the ATCM disables the automatic operation of the recirculation door.
SYSTEM OPERATION
A/C Compressor Control
The variable displacement A/C compressor is permanently driven by the engine. The flow of refrigerant through the A/C
compressor, and the resultant system pressure and evaporator operating temperature, is regulated by the refrigerant
solenoid valve. Operation of the refrigerant solenoid valve is controlled by the ATCM using a 400 Hz Pulse Width
Modulated (PWM) signal. The duty cycle of the PWM signal is calculated using the following parameters:
A/C compressor torque.
A/C compressor torque maximum.
A/C cooling status.
A/C demand.
A/C refrigerant pressure.
Ambient air temperature.
Blower speed.
Engine cranking status.
Evaporator temperature.
Transmission gear status.
