Discovery 2. Manual — part 293
AIR CONDITIONING
DESCRIPTION AND OPERATION
82-11
ATC ECU
The ATC ECU is installed in the centre of the fascia, below the radio. An integral control panel on the ATC ECU
contains switches for system control inputs and a LCD to provide system status information.
Inputs from sensors and the control panel switches are processed by the ATC ECU, which then outputs the
appropriate control signals.
ATC ECU connectors
ATC ECU connector pin details
Connector/Pin
No.
Description
Input/Output
C0791
1
Battery power supply
Input
2
Ignition power supply
Input
3
Sensor power supply
Output
4
Earth
-
5
Display illumination
Input
6
Not used
-
7
Not used
-
8
Sensor earth
-
C0792
1
Night lighting/dimming
Input
2
Vehicle speed
Input
3
Hand of drive
Input
4
Distribution flaps position
Input
5
Heater coolant temperature
Input
6
External air temperature
Input
7
In-car air temperature
Input
8
Blower power transistor collector voltage
Input
9
Not used
-
10
Not used
-
11
Windscreen heater status
Input
12
Rear screen heater status
Input
13
Rear air conditioning ON
Input
AIR CONDITIONING
82-12
DESCRIPTION AND OPERATION
Control panel
1 LH temperature switch
2 Economy mode (ECON) switch
3 Blower switch
4 Display
5 Distribution switch
6 External air temperature (EXT) switch
7 RH temperature switch
8 Fresh/Recirculated air switch
9 Defrost mode switch
10 Automatic mode (AUTO) switch
11 A/C on/off switch
14
Driver's blend flaps position
Input
15
Passenger's blend flaps position
Input
16
LH solar heating load
Input
17
RH solar heating load
Input
18
Evaporator
Input
19
Not used
-
20
Not used
-
C0793
1
Blower power transistor base current
Output
2
Blower relay
Output
3
Windscreen heater request
Output
4
Rear screen heater request
Output
5
Passenger's blend flaps servo motor, drive to hot
Output
6
Driver's blend flaps servo motor, drive to hot
Output
7
Distribution flaps servo motor, drive to windscreen and side
windows demist
Output
8
Fresh/Recirculated air servo motor, drive to recirculated air
Output
9
Cooling fan request (diesel models)
Output
10
Power relay
Output
11
Compressor clutch request
Output
12
Cooling fan request (V8 models)
Output
13
Passenger's blend flaps servo motor, drive to cold
Output
14
Driver's blend flaps servo motor, drive to cold
Output
15
Distribution flaps servo motor, drive to footwells
Output
16
Fresh/Recirculated air servo motor, drive to fresh air
Output
Connector/Pin
No.
Description
Input/Output
AIR CONDITIONING
DESCRIPTION AND OPERATION
82-13
The control panel switches are all non-latching pushswitches except for the LH and RH temperature switches, which
are centre-off rocker switches. The switches have the following functions:
LH and RH temperature switches. Enabled only while the system is on:
l
Each press increases or decreases the related temperature setting, in steps of 1
°
C (2
°
F), between 16 and 28
°
C (60 and 84
°
F).
l
If the decrease side of the switch is pressed when a temperature of 16
°
C (60
°
F) is set, the display changes to
LO (maximum cold).
l
If the increase side of the switch is pressed when a temperature of 28
°
C (84
°
F) is set, the display changes to
HI (maximum hot).
l
If a switch is kept depressed, step changes occur every 0.4 seconds.
A/C on/off switch. Switches the system on and off. When used to switch the system on, the system resumes the
configuration in use prior to the previous off selection.
Blower switch. Enabled only while the system is on. Provides manual control of blower speed:
l
Each press changes the blower speed, in sequence, through off (only available if economy mode is selected on)
and five incremental speeds.
l
If the switch is kept depressed, after 1 second subsequent speed increments occur every 0.4 second until blower
reaches high speed. Releasing and then pressing the switch again changes blower back to off or low speed.
Distribution switch. Enabled only while the system is on. Provides manual control of air distribution:
l
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.
l
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:
l
If the system is already on, the temperature output overrides the system outputs for approximately 7 seconds,
then the display reverts to system outputs.
l
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:
l
Switching between
°
F and
°
C on the display.
l
Switching the audible warning from off to on.
l
Switching the timed feet function on and off.
l
Switching the timed recirculated inlet air on and off.
l
Switching the latched recirculated inlet air on and off.
l
When there is a fault warning.
l
Running the self diagnostic routine.
AIR CONDITIONING
82-14
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.
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).
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