Air conditioning control system

AIR CONDITIONING CONTROL SYSTEM

The air conditioning control system comprises of relays, thermistor, dual pressure switch, and a control panel. Together these controls, in conjunction with the cooling fan, compressor clutch, and blower maintain the required environment inside the vehicle.

When air conditioning is not selected, air is supplied from the normal fresh air ventilators by ram effect. Heated air is circulated by the blower motor to the areas selected by the controls.

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 pushing the temperature control to cold, which automatically closes the heated coolant access to the heater matrix. Mixtures of cooled, fresh, and ambient air can be selected to give the required interior environmental conditions.

Trinary pressure switch

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

1. Refrigerant pressure drops below 2.0 bar (29.5₂ lbf/in ) (due to possible leakage), the compressor electro-mechanical clutch is disengaged. When pressure rises above 2.0 bar (29.5₂ lbf/in ) the compressor clutch is engaged.
2. Refrigerant pressure rises above 32 bar (455₂ lbf/in ) (due to possible blockage), even with maximum cooling fan operation, compressor electro-mechanical clutch is disengaged.
3. Refrigerant pressure exceeds 15 bar (220₂ lbf/in ), the cooling fan speed is increased by the Engine Control Module switching the cooling fan relays to provide 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.

The cooling fans are controlled by low and high temperature switches mounted in the top of the radiator. The cooling fans operate at slow speed providing the coolant temperature is normal. If the coolant temperature exceeds 114° C , the cooling fans will operate at high speed.

Blower control

The blower can be operated at any one of five 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 required button on the heater control panel. In recirculation position, air is drawn into the heater from the vehicle by closing the exterior air inlet and opening the interior air 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

Air from the blower unit is passed through the evaporator into the heater blend unit to be heated, if required. It is then directed into the vehicle interior according to the position of the flaps selected on the heater control unit. 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.