Air conditioning (Operation): Description and operation

Operation

General

Air conditioning operates only while the engine is running and the blower in the heater assembly is on (any speed). Fresh or recirculated air can be selected with or without the air conditioning being on, provided the ignition is on.

Air Conditioning

When the air conditioning switch is selected on, the indicator lamp in the switch illuminates and an air conditioning request signal is input to the ECM via the instrument pack and CAN Bus. The air conditioning request signal consists of a positive voltage supply via the blower switch and A/C switch, hard wired to the instrument pack. The instrument pack interprets the A/C request signal and informs the ECM of the condition using a message on the CAN Bus.

On K1.8 and non NAS KV6 models, the ECM is also in receipt of signals from the refrigerant pressure sensor and the evaporator temperature sensor, which it uses to determine the engine load, cooling fan speed and compressor clutch control. On Td4 and NAS KV6 models, the signals from the refrigerant pressure sensor and the evaporator temperature sensor are supplied to the instrument pack, which calculates the additional engine load and the cooling fan speed and transmits them to the instrument pack on the CAN Bus.

On receipt of the air conditioning request signal, the ECM switches air conditioning on by signalling the compressor clutch relay module to engage the compressor clutch and the cooling fan controller to run the cooling fans at the appropriate speed using a PWM signal. The engine drives the compressor to circulate the refrigerant. The blower draws fresh or recirculated air through the evaporator. As the air flows through the evaporator, moisture condenses out from the relatively warm air onto the cold evaporator. The dehumidified air is then fed into the heater assembly, from where it is distributed to the vehicle interior.

When the air conditioning switch is selected off, or if the blower is selected off, the indicator lamp in the air conditioning switch extinguishes and the air conditioning request signal is removed from the ECM. The ECM then switches air conditioning off by signalling the relay module to disengage the compressor clutch and cooling fan controller to terminate the operation of the cooling fans.

Blower Control The blower can be operated at any one of four speeds by rotating the blower switch to the required position. When the blower is switched off the air conditioning system will not operate.

The fresh air/recirculation flap has two positions and is operated by pressing the button in the centre console. In the recirculation position, air is drawn into the heater from the vehicle by closing the exterior air inlet and opening the interior inlet. In the fresh air position, air is drawn into the heater from outside the vehicle by opening the exterior air inlet and closing the interior inlet.

Heater Distribution and Blend Unit Control Blower unit air flow, having passed through the evaporator passes into the heater blend unit to be heated, if required. It is then directed into the vehicle interior in accordance with the flap positions, which are designated by the air distribution control on the fascia panel. A heater flap controls the amount of air flowing through the heater matrix, this flap is moved in response to temperature selection using the knob on the control panel.

The distribution control moves the flaps which control the direction of the air flow into the interior of the vehicle.