ATC Ecu
The ATC ECU is installed in the center 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.
| 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 |
| 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 de-mist | 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 |
The control panel switches are all non-latching push switches except for the LH and RH temperature switches, which are center-off rocker switches. The switches have the following functions:
LH and RH temperature switches. Enabled only while the system is on:
- 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).
- 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).
- 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).
- 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:
- Each press changes the blower speed, in sequence, through off (only available if economy mode is selected on) and five incremental speeds.
- 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:
- Each press changes the air distribution, in sequence, through footwells only, footwells and windscreen/side windows de-mist, windscreen/side windows de-mist 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.
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).