ATC ECU (page 4 of 5)

AIR CONDITIONING

DESCRIPTION AND OPERATION

82-23

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Maximum A/C Switch: For selection of maximum A/C when the ignition is on or rest heating when the ignition is 
off. A LED above the switch is illuminated when maximum cooling or rest heating is selected.

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Distribution Switches (Windscreen, Face and Footwell): For manual selection of air distribution in any 
combination of windscreen, face and footwell outlets. A LED above each switch illuminates when a selection is 
made.

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Defrost Programme Switch: Activates a programme that automatically selects the windscreen heater on, 
activates the compressor and changes the system settings to direct dry heat to the windscreen. A LED above 
the switch is illuminated while the defrost programme is active.

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Rear Window Heater Switch: Enabled only with the engine running. Pressing the switch energises the rear 
window heater for a set time period, until the switch is pressed again or until the engine stops, whichever occurs 
first. A LED above the switch is illuminated while the heater is on.

Inputs and Outputs
Five electrical connectors provide the interface between the ATC ECU and the vehicle/heater assembly wiring.

Both the low and high line systems receive ambient temperature, engine coolant temperature, engine speed and 
vehicle speed inputs in K bus messages from the instrument pack. If the K bus messages are missing or faulty, the 
ATC ECU adopts the following default values:

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Ambient temperature = 0 

°

C (32 

°

F)

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Engine coolant temperature = 80 

°

C (176 

°

F)

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Engine speed = 800 rev/min

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Vehicle speed = zero.

If a fault develops in the input from the temperature selector switch on the control panel, the ATC ECU adopts a default 
value of 24 

°

C (75 

°

F).

ATC ECU Harness Connector C0249 Pin Details

ATC ECU Harness Connector C0923 Pin Details

Pin No.

Description

System

Input/Output

Low

High

1

Front seat heating battery power supply

Yes

Yes

Input

2

LH front seat heater

Yes

Yes

Output

3

RH front seat heater

Yes

Yes

Output

Pin No.

Description

System

Input/Output

Low

High

1

Rear blower switch signal

No

Yes

Input

2

Rear blower switch power supply

No

Yes

Output

3

Automatic distribution switch

Yes

No

Input

4

LH heater matrix temperature sensor

No

Yes

Input

5

RH heater matrix temperature sensor

Yes

Yes

Input

6

Evaporator temperature sensor

Yes

Yes

Input

7

Blower control voltage

Yes

Yes

Output

8

Rear temperature switch

No

Yes

Input

9

Sensor ground (evaporator, and heater 
temperature sensors)

Yes

Yes

–

10 to 12

Not used

–

–

–

13

Recirculation flap motor signal 2

Yes

Yes

Input

14

Recirculation flap motor signal 2

Yes

Yes

Output

15

Recirculation flap motor signal 1

Yes

Yes

Output

16

Recirculation flap motor signal 1

Yes

Yes

Input

17

Rear blower and temperature switch 
power supply

No

Yes

Output

18

Not used

–

–

–