Discovery 2. Manual - part 712

AIR CONDITIONING

DESCRIPTION AND OPERATION

82-11

Temperature and distribution control

Figure shows flaps set for medium heat to face level and footwell outlets

1 Windscreen/Side windows outlet
2 Heater assembly casing
3 Air inlet
4 Evaporator
5 Heater matrix
6 Front footwells outlet
7 Rear footwells outlet
8 Face level outlet

AIR CONDITIONING

82-12

DESCRIPTION AND OPERATION

Control system
The control system operates the refrigerant system and the control flaps in the heater assembly to control the 
temperature and distribution of air in the vehicle interior. It also outputs signals to the fresh/recirculated air servo motor 
and the blower to control the volume and source of inlet air. The control system consists of:

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An Air Temperature Control (ATC) ECU.

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A dual pressure switch.

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An evaporator temperature sensor.

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An in-car temperature sensor.

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A sunlight sensor.

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A heater coolant temperature sensor.

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An ambient temperature sensor.

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

AIR CONDITIONING

DESCRIPTION AND OPERATION

82-13

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

Not connected

-

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

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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

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:

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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).

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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).

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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).

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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:

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Each press changes the blower speed, in sequence, through off (only available if economy mode is selected on) 
and five incremental speeds.

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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.