LR3/Disco 3
AMBIENT AIR TEMPERATURE SENSOR
The ambient temperature sensor is a Negative Temperature Coefficient (NTC) thermistor that provides the ATCM with an
input of external air temperature. The sensor is attached to a bracket on the rear of the bumper beam, on the vehicle
center-line.
REFRIGERANT PRESSURE SENSOR
The refrigerant pressure sensor provides the ATCM 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 ATCM 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 ATCM uses the signal from the refrigerant pressure sensor to protect the refrigerant system from extremes of
pressure and to calculate A/C compressor load on the engine. The ATCM also transmits the A/C compressor load value
to the Engine Control Module (ECM), via the medium speed CAN bus, instrument pack and high speed CAN bus, for use
in controlling the speed of the engine cooling fan.
To protect the system from extremes of pressure, the ATCM sets the A/C compressor to the minimum flow position if the
pressure:
Decreases to 1.9 ± 0.2 bar (27.5 ± 3 lbf/in
2
): the ATCM loads the A/C compressor again when the pressure
increases to 2.8 ± 0.2 bar (40.5 ± 3 lbf/in
2
).
Increases to 33 ± 1 bar (479 ± 14.5 lbf/in
2
): the ATCM loads the A/C compressor again when the pressure
decreases to 23.5 ± 1 bar (341 ± 14.5 lbf/in
2
).
EVAPORATOR TEMPERATURE SENSOR
