Air conditioning control system

AIR CONDITIONING CONTROL SYSTEM

The air conditioning control system comprises relays, thermistor, pressure switches, and a control panel. Inputs from outside the air conditioning system comprise temperature information from the engine cooling system. Together these controls, in conjunction with the cooling fans, compressor clutch, blower and heater distribution and blend unit enable minimal input to maintain the required environment inside the vehicle.

When air conditioning is not selected, air is supplied by ram effect or blower to the areas selected by the controls. The air mix flap on the blend unit controls the temperature of the air being splined. No cooled air is available.

Selecting air conditioning provides the added facility of cooled air available to be mixed as before. When required a fully cold condition can be selected by turning the temperature control to cold, which automatically closes the heated coolant access to the heater matrix. Mixtures of cooled, fresh, and hot air can be selected to give required interior environmental conditions by selection at the control panel.

Trinary switch – 1.4 and 2.0
Dual pressure switch – 1.6

This switch, located in the high pressure line between the condenser and the receiver drier, monitors refrigerant pressure and by means of the Fuel ECU controls the following system functions:

1. Refrigerant pressure drops below 2.0 bar, 29.5 lbf/in² (due to possible leakage), the compressors electro – mechanical clutch is dis – engaged.

When pressure rises above 2.0 bar, 29.5 lbf/in² the compressors clutch is re – engaged.

2. Refrigerant pressure rises above 32 bar, 455 lbf/in² (due to possible blockage), even with maximum cooling fan operation, compressor electro – mechanical clutch is dis – engaged.
3. Trinary switch only: Refrigerant pressure exceeds 18 bar, 255 lbf/in², the cooling fan speed is increased by the relays providing a direct feed to each fan motor.

Condenser cooling fans

The condenser cooling fans operate automatically whenever the air conditioning system is switched on, providing the system pressure is correct.

1.4 and 2.0 models: The cooling fans operate at slow speed providing the coolant temperature is normal. If the coolant temperature reaches 114°C, the cooling fans will operate at high speed. On Turbo models, the fans are controlled via the MEMS ECU. On 1.4 and 2.0 naturally aspirated models, the fans are controlled by the low and high temperature coolant switches.

1.6 models: The cooling fans operate at normal speed whenever the air conditioning is switched on.

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 can move to two positions. One position covers the outside air inlet, leaving open an inlet from the inside of the car, when recirculated air is required. In the other position it will cover the inlet from the inside of the car leaving open the outside air inlet, when fresh air is required.

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 by the temperature control.

A cable connected to the bleed flap linkage moves the coolant valve, allowing engine coolant to flow through the heater matrix back to the engine when the control is moved towards the hot position. The temperature of the heated air flow into the vehicle interior is controlled by the blend flap.

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