Refrigerant Pressure Sensor / Switch: Description and Operation

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.