Discovery 2. Manual - part 713

AIR CONDITIONING

DESCRIPTION AND OPERATION

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Distribution switch. Enabled only while the system is on. Provides manual control of air distribution:

Each press changes the air distribution, in sequence, through footwells only, footwells and windscreen/side
windows demist, windscreen/side windows demist only, face level only, face level and footwells.

If the switch is kept depressed, after 1 second subsequent distribution changes occur every 0.4 seconds until
distribution reaches face level and footwells. Releasing and then pressing the switch again changes distribution
back to footwells only.

External air temperature (EXT) switch. Enabled while the system is on or off. Switches the external temperature output
on and off:

If the system is already on, the temperature output overrides the system outputs for approximately 7 seconds,
then the display reverts to system outputs.

If the system is switched on while the external temperature output is on, the system outputs override the external
temperature output.

Fresh/Recirculated air switch. Enabled only while the system is on. Provides manual control of inlet air selection.

Defrost mode switch. Starts the system in, or switches the system to and from, defrost mode.

Automatic mode (AUTO) switch. Starts the system in, or switches the system to and from, the automatic mode.

Economy mode (ECON) switch. Enabled only while the system is on. Provides manual on/off control of the refrigerant
system compressor, to reduce fuel consumption when there is no requirement for cool or dehumidified air, e.g. when
the ambient temperature is lower than the LH and RH temperature settings.

Temperature settings: The LH and RH temperature settings are reference inputs used by the control system and give
an approximation of the temperatures that will be established in the cabin. They are not necessarily actual distribution
outlet temperatures, or the temperatures at specific points in the cabin.

Audible warning: A 'beep' is emitted from the ATC ECU each time it receives a control switch input. This audible
warning can be switched off and on by pressing and holding the AUTO switch, then pressing and holding the A/C on/
off switch until the audible warning sounds (approximately 3 seconds). While switched off, the audible warning still
sounds when:

Switching between

F and

C on the display.

Switching the audible warning from off to on.

Switching the timed feet function on and off.

Switching the timed recirculated inlet air on and off.

Switching the latched recirculated inlet air on and off.

When there is a fault warning.

Running the self diagnostic routine.

AIR CONDITIONING

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DESCRIPTION AND OPERATION

Display outputs

1 LH temperature
2 Economy mode
3 Recirculated air
4 Automatic mode

5 Manual distribution
6 RH temperature
7 Blower speed
8 External air temperature

Outputs on the display are shown at full brightness when the exterior lights are off, and dimmed when the exterior
lights are on.

LH temperature. Illuminates to show the LH temperature selection, the temperature scale or that the ATC ECU is in
diagnostic mode.

Economy mode. Illuminates when the compressor is manually selected off with the ECON switch.

Recirculated air. Illuminates when the inlet air is manually selected to recirculated mode.

Automatic mode. Illuminates the AUTO legend and related symbol(s) when the blower speed, air distribution or
temperature control are in the automatic mode.

Manual distribution. Illuminates the appropriate symbol(s) to show the manually selected air distribution. Also
illuminates in the automatic modes when one of the temperatures is set to LO or HI.

AIR CONDITIONING

DESCRIPTION AND OPERATION

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RH temperature. Illuminates to show the RH temperature selection, external air temperature or diagnostic fault code.

Blower speed. Illuminates when the blower speed is manually selected. Also illuminates in the automatic modes when
one of the temperatures is set to LO or HI.

External air temperature. EXT illuminates to show that external air temperature is selected on.

All temperature indications on the display are in either

C or

F. For 1 second after the system is first switched on, the

display shows only

C or

F, in the LH temperature window, to indicate which temperature scale is in use. After 1

second, the

C or

F indication goes off and the display shows all relevant outputs.

Temperature conversion: While the system is on, the temperature indications on the display can be switched between
the two scales by pressing and holding the fresh/recirculated air switch, then pressing and holding the A/C on/off
switch until the audible warning sounds (approximately 3 seconds).

Dual pressure switch
The dual pressure switch protects the refrigerant system from extremes of pressure. The normally closed switch is
installed in the top of the receiver drier. If minimum or maximum pressure limits are exceeded the switch contacts
open, causing the compressor clutch to be disengaged. The minimum pressure limit protects the compressor, by
preventing operation of the system unless there is a minimum refrigerant pressure (and thus refrigerant and
lubricating oil) in the system. The maximum pressure limit keeps the refrigerant system within a safe operating
pressure.

Dual pressure switch nominal operating pressures

Evaporator temperature sensor
The evaporator temperature sensor is an encapsulated thermistor that provides the ATC ECU with an input of the
evaporator air outlet temperature. The evaporator temperature sensor is installed in a clip which locates in the
evaporator matrix in the heater assembly. The ATC ECU uses the input to prevent the formation of ice on the
evaporator.

In-car temperature sensor
The in-car temperature sensor is an encapsulated thermistor that provides the ATC ECU with an input of cabin air
temperature. The sensor is integrated into the inlet of an electric fan, which is installed behind a grille in the fascia
outboard of the steering column. The fan runs continuously, while the ignition is on, to draw air through the grille and
across the sensor.

Sunlight sensor
The sunlight sensor consists of two diodes that provide the ATC ECU 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 used as a measure of the
solar heating effect on vehicle occupants. The sensor is installed in the centre of the fascia upper surface.

Heater coolant temperature sensor
The heater coolant temperature sensor is an encapsulated thermistor that provides the ATC ECU with an input related
to heater matrix coolant temperature. The sensor is installed in the casing of the heater assembly and presses against
the end tank of the heater matrix.

Ambient temperature sensor
The ambient temperature sensor is an encapsulated thermistor that provides the ATC ECU with an input of external
air temperature. The sensor is attached to the cooling fan mounting bracket in front of the condenser.

Limit

Opening pressure, bar (lbf.in

)

Closing pressure, bar (lbf.in

)

Minimum

2.0 (29.0), pressure decreasing

2.3 (33.4), pressure increasing

Maximum

32 (464), pressure increasing

26 (377), pressure decreasing

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DESCRIPTION AND OPERATION

Operation

General
While the system is on, the ATC ECU operates the refrigerant system and the inlet air, blower speed, air temperature
and air distribution functions to produce the conditions requested on the control panel. When the system is first
switched on, the ATC ECU resumes the control outputs in use when the system was last switched off. If conditions
have changed, or a different mode is selected to switch the system on, the control outputs are then changed to
produce the required new settings.

The system operates in automatic, economy and defrost modes, with manual overrides of the inlet air source, blower
speed and air distribution. The air temperature is automatically controlled in all operating modes.

In the automatic mode, the ATC ECU operates the system to warm-up or cool down the cabin to establish and
maintain the temperature selections on the control panel, while directing the air to those outlets most comfortable for
the occupant(s). If a difference between the LH and RH temperature selections causes a conflict of the required inlet
air source, blower speed or air distribution settings, priority is given to achieving the temperature requested on the
driver's side of the control panel.

The ATC ECU enters the economy mode when the refrigerant compressor is selected off while the system is in the
automatic mode, which reduces the load on the engine. Economy mode operation is similar to the automatic mode,
but without the ability to cool the cabin if the ambient temperature is higher than the temperature selections made on
the control panel, or to dehumidify the air in the cabin.

In the defrost mode, the ATC ECU sets the inlet air source to fresh air, the blower to maximum speed, the air
distribution to windscreen and side windows, and outputs signals to the BCU to operate the rear window heater and
(where fitted) the windscreen heater. The BCU starts or, if the heaters are already on, resets the heater timers and
energises the rear window and windscreen heaters for a complete on cycle.

Air temperature control
To determine the amount of heat or cooling required by the cabin, the ATC ECU uses the sensor inputs and the
temperatures selected on the control panel to calculate target air outlet temperatures for the driver's and the front
passenger's side of the heater assembly. The ATC ECU then signals the servo motors controlling the respective blend
flaps in the heater assembly to move to the flaps to the appropriate position. The target temperatures are constantly
updated and, in the automatic mode, also used in further calculations to determine the inlet air source, the blower
speed and the air distribution.

Inlet air control
The inlet air source is automatically controlled while the system is off or on. While the system is on, the inlet air source
can also be manually controlled to give timed recirculated air or latched recirculated air.

While the system is off, the ATC ECU uses vehicle speed to determine the inlet air source. With the vehicle at rest,
the inlet air source is set to recirculated air. When vehicle speed reaches 17.5 mph (28 km/h), the inlet air source
changes to fresh air. The inlet air source then remains at fresh air until the vehicle speed decreases to 5 mph (8 km/
h), when it returns to recirculated air.

While the system is on, the ATC ECU uses the LH and RH temperature selections, vehicle speed, ambient air
temperature and coolant temperature to determine the inlet air source. In the automatic mode:

If one temperature selection is set to LO and one is set to a specific temperature or HI, the inlet air is set to
recirculated air.

If one temperature selection is set to HI and one is set to a specific temperature or HI, the inlet air is set to fresh
air.

When specific LH and RH temperature selections are set, the inlet air source remains at fresh air except when
the air distribution function is set to face level only or face level and footwell outlets. If the air distribution function
is set to face level only or face level and footwell outlets, at 56 mph (90 km/h) the inlet air source changes to
recirculated air (to exclude ram effect, which becomes excessive at speed). When the vehicle speed decreases
to 37.5 mph (60 km/h), the inlet air source returns to fresh air.

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