L322 Range Rover System Description and Operation
AIR CONDITIONING
DESCRIPTION AND OPERATION
82-25
Sensors
Both the low and the high line systems incorporate:
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An in-car temperature sensor
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A refrigerant pressure sensor
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An evaporator temperature sensor
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A heater matrix temperature sensor.
The high line system also incorporates:
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A second heater matrix temperature sensor
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A sunlight sensor
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A pollution sensor.
In-car Temperature Sensor
The in-car temperature sensor is an encapsulated Negative Temperature Coefficient (NTC) thermistor that provides
the ATC ECU with an input of passenger compartment air temperature. The in-car temperature sensor is installed
behind a grille in the ATC ECU control panel. An electric fan in the ATC ECU runs continuously, while the ignition is
on, to draw air through the grille and across the in-car temperature sensor.
The ATC ECU uses the signal from the in-car temperature sensor for control of the coolant temperature valve(s),
blower speed and air distribution.
The signal voltage from the in-car temperature sensor is between 0 and 5 V. The ATC ECU monitors the signal voltage
and defaults to a temperature of 20
°
C (68
°
F) if it goes out of the range 0.573 – 4.882 V:
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If the signal voltage is less than 0.573 V, the ATC ECU assumes there is a short circuit to ground
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If the signal voltage is more than 4.882 V, the ATC ECU assumes there is an open circuit or a short circuit to
battery.
Refrigerant Pressure Sensor
The refrigerant pressure sensor provides the ATC ECU with a pressure input from the high pressure side of the
refrigerant system. The refrigerant pressure sensor is located in the refrigerant line between the condenser and the
thermostatic expansion valve.
The ATC ECU supplies a 5 V reference voltage to the refrigerant pressure sensor and receives a return signal voltage,
between 0 and 5 V, related to system pressure.
The ATC ECU uses the signal from the refrigerant pressure sensor to protect the system from extremes of pressure
and to calculate compressor load on the engine for idle speed control. The ATC ECU also transfers the pressure value
to the Engine Control Module (ECM), via the K bus, instrument pack and CAN bus, for use in controlling the speed of
the engine cooling fan.
To protect the system from extremes of pressure, the ATC ECU disengages the compressor clutch if the pressure:
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Decreases to 1.9
±
0.2 bar (27.5
±
3 lbf/in
2
): the ATC ECU engages the compressor clutch again when pressure
increases to 2.8
±
0.2 bar (40.5
±
3 lbf/in
2
)
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Increases to 33
±
1 bar (479
±
14.5 lbf/in
2
): the ATC ECU engages the compressor clutch again when pressure
decreases to 23.5
±
1 bar (341
±
14.5 lbf/in
2
).
Evaporator Temperature Sensor
The evaporator temperature sensor is a NTC thermistor that provides the ATC ECU with a temperature signal from
the air outlet side of the evaporator. The evaporator temperature sensor is installed in the RH side of the heater
assembly casing, and extends into the core of the evaporator.
The ATC ECU uses the input from the evaporator temperature sensor to control the engagement and disengagement
of the compressor clutch, to prevent the formation of ice on the evaporator.
The signal voltage from the evaporator temperature sensor is between 0 and 5 V. The ATC ECU monitors the signal
voltage and defaults to a temperature of 0
°
C (32
°
F) if it goes out of the range 0.157 – 4.784 V:
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If the signal voltage is less than 0.157 V, the ATC ECU assumes there is a short circuit to ground
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If the signal voltage is more than 4.784 V, the ATC ECU assumes there is an open circuit or a short circuit to
battery.
