L322 Range Rover System Description and Operation
AIR CONDITIONING
DESCRIPTION AND OPERATION
82-41
Engine Idle Speed Control
The ATC ECU signals the ECM to increase engine idle speed settings if a high current application is switched on or
if low battery voltage is detected. The signal consists of a message transmitted via the K bus, instrument pack and
CAN bus, and increases idle speed between 100 and 200 rev/min. The ATC ECU requests the engine idle speed
increase when the following high current applications are switched on:
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Rear window heater
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Blower, at speed 6 or 7
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Headlamp main beam.
The engine idle speed increase is also requested if battery voltage decreases to less than 11.4 V. The speed increase
request is discontinued when battery voltage increases to more than 12.2 V again.
Engine Cooling Fan Control
The engine's electric cooling fan is controlled by the ECM. When the compressor is engaged the ATC ECU sends a
fan speed message between 0 (off) and 15 (maximum speed) to the ECM, via the K bus, instrument pack and CAN
bus. The ATC ECU requests the cooling fan on when:
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The vehicle speed is less than 44 mph (70 km/h)
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There is no fault with the compressor clutch circuit
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Battery voltage is less than 16 V.
The fan speed requested depends on the pressure in the refrigerant system. The higher the pressure the faster the
fan speed that is requested. When vehicle speed increases to more than 50 mph (80 km/h) the ATC ECU changes
the fan speed request to 0 until vehicle speed decreases to less than 44 mph (70 km/h) again.
If battery voltage increases to more than 16 V for 5 seconds the ATC ECU changes the fan speed to 0 until the voltage
decreases to less than 15.8 V.
Temperature Control
To determine the amount of heat required, in the form of coolant flow through the heater, the ATC ECU compares the
reference value with the heater matrix temperature and incorporates a correction factor to compensate for changes
of coolant flow rate with engine speed. From the resultant value the ATC ECU determines the open duration of the
coolant valve and outputs the appropriate control signal. On the high line system, separate values and output signals
are generated for each coolant valve to produce the individual temperature control for the LH and RH sides of the
passenger compartment.
When the temperature setting on the control panel is set to maximum, the ATC ECU signals the coolant valve to
remain open. When the temperature setting on the control panel is set to minimum, the ATC ECU signals the coolant
valve to remain closed.
On the high line system, the minimum setting is over-ridden when the defrost programme, maximum A/C, rest heating
or FBH functions are selected.