Air Conditioning Control System (page 3 of 5)

The evaporator temperature sensor is also used in conjunction with the refrigerant pressure sensor to facilitate compressor load prediction for optimum idle speed control and load management. The A/C system places an extra load on the engine when the compressor is operating, so the ECM automatically adjusts the idle speed to compensate for the additional load. ENGINE MANAGEMENT SYSTEM - MEMS, DESCRIPTION AND OPERATION, Description. ENGINE MANAGEMENT SYSTEM - EDC, DESCRIPTION AND OPERATION, Description. ENGINE MANAGEMENT SYSTEM - SIEMENS (ALL EXCEPT NAS), DESCRIPTION AND OPERATION, Description. ENGINE MANAGEMENT SYSTEM – SIEMENS (NAS), DESCRIPTION AND OPERATION, Description.

Refrigerant Pressure Sensor The refrigerant pressure sensor is located in the refrigerant lines. On LHD vehicles with KV6 engines it is located at the RH side of the engine compartment close to the outlet from the condenser in the refrigerant line leading to the thermostatic expansion valve. On all other engine/vehicle derivatives the sensor is located in the same refrigerant line at the LH side of the engine compartment. The refrigerant pressure sensor provides the ECM with a pressure input from the high pressure side of the refrigerant system.

The ECM uses the signal from the refrigerant pressure sensor to protect the system from extremes of pressure, by disengaging the compressor clutch. The signal is also used for cooling fan control. The temperature sensor used has a low pressure range of 0 – 600 psi and provides the following functions: l Provide a safety cut-out function if the refrigerant pressure goes either too high or too low. l Indicate when the refrigerant pressure reaches such a point that additional cooling is required – if the pressure reaches the medium point, the cooling fans will be switched to high speed. l The pressure sensor is used in conjunction with the evaporator temperature sensor to predict compressor load for load management at idle/part throttle.

On K1.8 and non NAS KV6 models, the refrigerant pressure sensor signal is fed directly to the ECM. On Td4 and NAS KV6 models, the refrigerant pressure sensor is connected to the instrument pack, and the signal is relayed to the ECM from the instrument pack via the CAN Bus.

Because the compressor is lubricated by oil suspended in the refrigerant, a low pressure signal from the sensor is used by the ECM to prevent operation of the compressor unless there is a minimum refrigerant pressure, and thus refrigerant and oil in the system.

Control Switches The control switches consist of two latching push switches installed in the centre console, an air conditioning switch and a fresh/recirculated air switch. Each switch contains an amber indicator lamp which illuminates when air conditioning or recirculated air is selected, as applicable.

The A/C switch is supplied with a positive feed through the blower motor switch when one of the four blower speeds is selected. When the A/C switch is selected, a signal is supplied to the instrument pack through a hard wire connection. The instrument pack interprets the A/C request signal and transfers the request to the ECM via the CAN bus. INSTRUMENTS, DESCRIPTION AND OPERATION, Description.

Compressor Clutch Relay The compressor clutch relay switches power to the compressor clutch under the control of the ECM. The relay is located in the engine compartment fusebox. The compressor clutch is energized to engage and de-energized to disengage.

Compressor Operation of the clutch is controlled by the engine control module (ECM). To protect the refrigerant system from unacceptably high pressure, a pressure relief valve is installed in the outlet side of the compressor. The pressure relief valve is set to operate at 3430 kPa (497.5 lbf.in) and vents excess pressure into the engine compartment.