Coolant Valve

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 an SU (Td6) or YG (V8) wire. The ECT sensor is a Negative Temperature Coefficient (NTC) sensor. By measuring the voltage returned on an NG (Td6) or 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.