L322 Range Rover System Description and Operation
AIR CONDITIONING
82-46
DESCRIPTION AND OPERATION
Rear Passenger Face Level Air (High Line System Only)
The volume and temperature of the air from the rear passenger face vent are adjusted with the thumbwheels at the
sides of the vent assembly. Each thumbwheel operates a variable potentiometer connected to the ATC ECU. The
volume thumbwheel controls stepless changes of rear blower speed between off and full speed. The temperature
thumbwheel controls the position of the rear passenger face level blend flap in the heater assembly when the driver's
side reference temperature is more than 0%.
Volume Control: The volume potentiometer outputs between 0 and 5 V to the ATC ECU. The ATC ECU translates the
voltage from the potentiometer into a signal voltage for the output stage in the rear blower. Potentiometer voltages of
less than 1.25 V are interpreted as a blower off selection and translate into a signal voltages less than 0.1 V.
Potentiometer voltages between 1.25 and 5 V are translated into proportional signal voltages between 0.1 and 5 V.
The ATC ECU automatically switches off the rear blower when:
l
The defrost programme is active
l
The main blower is selected off
l
The engine cranks
l
The ignition is selected off (the rear blower remains off during rest heating, parked heating and parked
ventilation).
Temperature Control: The temperature potentiometer outputs between 0 and 5 V to the ATC ECU. The ATC ECU
translates the voltage from the potentiometer into a blend flap position between 0% (cold) and 100% (hot) and outputs
the appropriate control signal on the M bus to the blend flap motor. Potentiometer voltages of less than 1.5 V translate
to a blend flap position of 0%. Potentiometer voltages of more than 3.4 V translate to a blend flap position of 100%.
Potentiometer voltages between 1.5 and 3.4 V translate linearly to blend flap positions between 0 and 100%.
Windscreen Heater (Where Fitted)
When the engine is running and the windscreen heater is selected on, the ATC ECU illuminates the LED above the
switch and energises the heated front screen relay attached to the passenger end of the fascia cross tube. If not
already active, the ATC ECU also activates the A/C compressor and the blower, and sets air distribution to
windscreen. After 10 minutes (when ambient temperature is –15
°
C (5
°
F) or above) or 17 minutes (when ambient
temperature is less than –15
°
C (5
°
F)), the ATC ECU extinguishes the LED and de-energises the heated front screen
relay. After the heater times out or is switched off, the timer in the ATC ECU is reset to zero.
Rear Window Heater
When the engine is running and the rear window heater is selected on, the ATC ECU illuminates the LED above the
switch and energises the rear window heater relay on the rear fusebox. After 10 minutes (when ambient temperature
is –15
°
C (5
°
F) or above) or 17 minutes (when ambient temperature is less than –15
°
C (5
°
F)), the ATC ECU
extinguishes the LED and operates the rear window heater at low power for 60 minutes. During the 60 minutes, the
ATC ECU cycles the rear window heater relay off for 80 seconds and on for 40 seconds. If the rear window heater
switch is pressed again during the low power phase, the ATC ECU illuminates the LED again and returns the rear
window heater to full power by keeping the rear window heater relay energised for 5 minutes. At the end of the 5
minutes the LED is extinguished and the 60 minutes low power phase is repeated.
The ATC ECU outputs a K bus message when the rear window heater is active. The message allows the navigation
computer to compensate for the effect of the magnetic field generated when the rear window heater is active. The
BCU transfers the message onto the P bus for the door modules, which activate the door mirror heaters together with
the rear window heater.
Washer Jet Heaters
The ATC ECU automatically energises the washer jets relay, on the passenger compartment fusebox, when the
ignition is on and the ambient temperature is less than 3
°
C (37
°
F). If the ambient temperature increases to more
than 6
°
C (43
°
F), the ATC ECU de-energises the washer jets relay.
Parked Ventilation
Parked ventilation allows the vehicle interior to be ventilated with ambient air while parked with the engine stopped.
Vehicles without a FBH have parked ventilation only. On vehicles with a FBH, parked ventilation operates in
conjunction with parked heating (see Parked Heating/Ventilation below).
