Range Rover P38
82
AIR CONDITIONING
NEW RANGE ROVER
18
DESCRIPTION AND OPERATION
Distribution
The ATC ECU supplies battery voltage to the
distribution servo to set the position the distribution
flaps in the heater unit. To change the direction of
drive, the ATC ECU reverses the polarity of the
supply. When the system is in the automatic mode,
the ATC ECU determines the required position of the
distribution flaps from the ambient air temperature and
the solar heating load. The distribution can be set
manually using the five distribution switches.
Demist mode
When the PROG switch is pressed, the ATC ECU
overrides the automatic and manual selections and
operates the heating and ventilation system in the
demist mode. A second press of the PROG switch
returns the system to the previous settings. While the
automatic demist mode is engaged, the windscreen
and rear screen heaters can be operated to reset their
timer start point without effecting the demist
programme.
Cold start up
If the heater coolant temperature and ambient air
temperature are relatively low when the air
conditioning is switched on, the ATC ECU delays
operation of the blowers to avoid blowing cold air into
the vehicle. As the heater coolant temperature
increases, so the ATC ECU progressively increases
the speed of the blowers to heat up the vehicle interior
to the target air temperatures. As the in-car
temperature approaches the target temperatures,
blower speed decreases.
Hot start up
If the ambient temperature is relatively high when the
air conditioning is switched on, the ATC ECU initially
runs the blowers at slow speed and sets the inlet air
source to fresh air in order to purge the stagnant air
from the system. After approximately 60 seconds the
ATC ECU then switches the inlet air source to
recirculated air and progressively increases the speed
of the blowers to cool down the vehicle interior. As the
in-car temperature approaches the target
temperatures, blower speed decreases.
Ambient temperature damping
When the ambient temperature increases, the ATC
ECU imposes a rate of change limit of 0.5
°
C (1
°
F)
/minute. When the ambient temperature is decreasing,
the ATC ECU accepts an unlimited rate of change.
Ambient temperature input strategy (from VIN
381431)
The ATC ECU incorporates a software strategy to
overcome the effect of radiant heat from the engine
and cooling systems on the ambient temperature
sensor:
•
At vehicle speeds of 15 mph (24 km/h) and
above, the input is considered valid and
changes are accepted. The value of the
input is stored in memory and constantly
updated while the vehicle speed is above
15 mph (24 km/h).
•
At vehicle speeds below 15 mph (24 km/h),
changes of input are considered suspect
and changes are ignored. In place of the
actual input, the ATC ECU uses the value
stored in memory.
•
When the ignition is switched on, if the
ATC ECU detects warm heater coolant, it
uses the ambient temperature stored in
memory. If the ATC ECU detects cold
coolant, it uses the input from the ambient
temperature sensor.
