Air Conditioning Control System
Air Conditioning Control System
The air conditioning control system comprises relays, thermostat, 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 supplied. 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 controls 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.
Dual pressure switch
This switch, located in the high pressure line between the receiver drier and the expansion valve, monitors refrigerant pressure and by means of the relay module controls the following system functions:
1. Refrigerant pressure drops below 2.0 bar, 29 lbf/Sq in (due to possible leakage), the compressor's electro-mechanical clutch is dis-engaged.
When pressure rises above 2.0 bar, 29 lbf/Sq in the compressor's clutch is re-engaged.
2. Refrigerant pressure rises above 32 bar, 455 lbf/Sq in (due to possible blockage), even with cooling fan operation, the compressor's electro-mechanical clutch is dis-engaged.
When the pressure drops below 26 bar, 375 lbf/Sq in the compressor clutch is re-engaged.
Condenser cooling fans
The condenser cooling fans operate automatically whenever the air conditioning system is switched on.
Fan timer unit
The thermostatically controlled timer will continue to operate the cooling fans after the air conditioning or ignition is switched off. When the system temperature is excessive, the fans will operate for 10 minutes to reduce condenser and underbonnet temperature.
Blower control
The blower can be operated at any one of four speeds by sliding the blower switch to the required position. When the blower is switched off the air conditioning system will not operate.
The fresh air/recirculation flaps can move between two positions. One position covers the outside air inlet, leaving open an inlet from the inside of the vehicle clear, when recirculated air is required. In the other position they will cover the inlet from the inside of the vehicle 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 designated by the air distribution control. Heater flaps control the amount of air flowing through the heater matrix. These flaps are controlled individually by the driver's and passenger's temperature controls.
When the temperature control is in the cold position, a micro switch actuates a vacuum control to close the coolant valve on the engine. As the temperature control is moved away from cold, the coolant valve is opened allowing heated engine coolant to flow through the heater matrix. The temperature of the heated air flow into the vehicle interior is controlled by the blend flaps.
The distribution control moves the flaps which control the direction of the air flow into the interior of the vehicle.