AIR CONDITIONING (Description): DESCRIPTION AND OPERATION (page 13 of 13)

AIR CONDITIONING

DESCRIPTION AND OPERATION

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Dual pressure switch
The dual pressure switch protects the refrigerant system from extremes of pressure. The normally closed switch is 
installed in the top of the receiver drier. If minimum or maximum pressure limits are exceeded the switch contacts 
open, causing the compressor clutch to be disengaged. The minimum pressure limit protects the compressor, by 
preventing operation of the system unless there is a minimum refrigerant pressure (and thus refrigerant and 
lubricating oil) in the system. The maximum pressure limit keeps the refrigerant system within a safe operating 
pressure.

Dual pressure switch nominal operating pressures

Evaporator temperature sensor
The evaporator temperature sensor is an encapsulated thermistor that provides the ATC ECU with an input of the 
evaporator air outlet temperature. The evaporator temperature sensor is installed in a clip which locates in the 
evaporator matrix in the heater assembly. The ATC ECU uses the input to prevent the formation of ice on the 
evaporator.

In-car temperature sensor
The in-car temperature sensor is an encapsulated thermistor that provides the ATC ECU with an input of cabin air 
temperature. The sensor is integrated into the inlet of an electric fan, which is installed behind a grille in the fascia 
outboard of the steering column. The fan runs continuously, while the ignition is on, to draw air through the grille and 
across the sensor.

Sunlight sensor
The sunlight sensor consists of two diodes that provide the ATC ECU with inputs of light intensity, one as sensed 
coming from the left of the vehicle and one as sensed coming from the right. The inputs are used as a measure of the 
solar heating effect on vehicle occupants. The sensor is installed in the centre of the fascia upper surface.

Heater coolant temperature sensor
The heater coolant temperature sensor is an encapsulated thermistor that provides the ATC ECU with an input related 
to heater matrix coolant temperature. The sensor is installed in the casing of the heater assembly and presses against 
the end tank of the heater matrix.

Ambient temperature sensor
The ambient temperature sensor is an encapsulated thermistor that provides the ATC ECU with an input of external 
air temperature. The sensor is attached to the cooling fan mounting bracket in front of the condenser.

Limit

Opening pressure, bar (lbf.in

2

)

Closing pressure, bar (lbf.in

2

)

Minimum

2.0 (29.0), pressure decreasing

2.3 (33.4), pressure increasing

Maximum

32 (464), pressure increasing

26 (377), pressure decreasing