Automatic Temperature Control (ATC)

AUTOMATIC TEMPERATURE CONTROL (ATC)

DESCRIPTION

General
The Automatic Temperature Control (ATC) system is controlled by the ATC ECU, which is located behind the centre console. ATC features automatic control of a common temperature setting for both sides of the passenger compartment, with manual control of the blower speed, air recirculation, and air distribution.

A Fuel Burning Heater (FBH) is fitted as an option on V8 vehicles.

OPERATION

Power Distribution
Feed from the positive battery terminal (C0192) is supplied to the following on an R wire:
- Maxi fuse 61.
- Maxi fuse 64.
- Fuse12
- Fuse53.

All are located in the passenger compartment fuse box (C0632). Maxi fuse 61 (C0581) provides a constant battery feed to the cooling fan control unit (C0005) on an RU then U wire. Maxi fuse 64 (C0580) provides a constant battery feed to the blower motor control unit (C2281) on an RU then YG wire.

Fuse 12 (C0586) provides a constant battery feed to the ATC ECU (C1630) on an RP wire. The ATC ECU (C1630) is earthed on an N wire.

Fuse 53 (C0583) provides a constant battery feed to the ignition switch (C0028 on V8 vehicles) on an R wire. When the ignition switch is turned to the 'ignition' position, current flows across the switch (C0028 on V8 vehicles) to fuse 34 of the passenger compartment fuse box (C0585) on a G wire. Fuse 34 (C0587) provides an ignition feed to the ATC ECU (C1629) on a GY wire.

Compressor
When compressor operation is required, the ATC ECU (C1629) sends a message to the Engine Control Module (ECM) via the K bus on a WRY wire. Provided there are no engine management constraints, the ECM (C033 1) responds by increasing throttle angle and fuelling and returns a signal granting operation of the compressor to the ATC ECU (C1629) on a BG wire. The ATC ECU (C163O) then provides a feed to the compressor clutch (C0182)
on a BS wire.

Refrigerant Pressure Sensor
The refrigerant pressure sensor is located in the refrigerant line between the condenser and the thermostatic expansion valve. It provides the ATC ECU with a pressure input from the high pressure side of the refrigerant system. The ATC ECU (C1629) provides a 5 V reference feed to the pressure sensor (C1610) on a GY wire. The pressure sensor (C1610)
returns a signal voltage of between 0 V and 5 V, depending upon system pressure, to the ATC ECU (C1629) on a BS wire. The ATC ECU (C1629) provides an earth path for the pressure sensor (C1610) on an NB wire.

Evaporator Temperature Sensor
The evaporator temperature sensor is a Negative Temperature Coefficient (NTC) sensor. The ATC ECU (C0923) provides a feed to the evaporator temperature sensor (C0417) on an NB wire. By measuring the voltage returned on a YB wire, the ATC ECU (C0923) can determine evaporator temperature.

Blower Motor
Operation of the blower motor is controlled by the ATC ECU via the blower motor control unit. To control blower motor speed, the ATC ECU (C0923) provides a stepped voltage of between 0 V and 8 V to the control unit (C2281) on a UR wire. This is used by the control unit to regulate the supply voltage from maxi fuse 64 of the passenger compartment fuse box to the blower motor (C0056) on BG and RG wires.

The blower motor control unit (C2281) is earthed on an N wire.

Heater Coolant Temperature Sensor
The heater coolant temperature sensor is a Negative Temperature Coefficient (NTC) sensor. The ATC ECU (C0923) provides a feed to the temperature sensor (C0416) on an NB wire. By measuring the voltage returned on the YR wire, the ATC ECU (C0923) can determine the temperature of the air exiting the heater matrix.

Coolant Valve
A single coolant valve is fitted on the ATC system to control coolant flow to the heater matrix. The coolant valve (C2034) is controlled by a Pulse Width Modulated (PWM) signal from the ATC ECU (C1629) on a YN wire.

Auxiliary Coolant Pump
The auxiliary coolant pump is used to ensure a satisfactory flow rate through the heater matrix at low engine speeds. The ATC ECU (C1629) provides a feed to the pump (C2035) on a UG wire. The pump (C2035) is earthed on an N wire.

Cooling Fan
Operation of the cooling fan is controlled by the ECM. When the compressor is engaged, the ATC ECU (C1629) informs the ECM (C0331) via the K bus on a WRY wire that cooling fan operation is required. The ATC ECU also informs the ECM of the speed at which the fan should be driven.

The ECM also monitors Engine Coolant Temperature (ECT) to determine fan speed. The ECM (C0606) provides a feed to the ECT sensor (C0169) on a YG (V8) wire. The ECT sensor is a Negative Temperature Coefficient (NTC) sensor. By measuring the voltage returned on a NO (V8) wire, the ECM can determine engine coolant temperature.

The ECM (C0331) now provides a feed to the cooling fan control unit (C0005) on a BG wire. This is used by the control unit to regulate the supply voltage from maxi fuse 61 of the passenger compartment fuse box (C0581) on an RU wire.