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11.9.2 The evaporator sensor
The evaporator sensor is a temperature detector.
Role:
g
Sensing the evaporator temperature
g
Preventing the freeze of the evaporator by
stopping cold generation
The compressor generally disengages when the
detected temperature achieves -1°C, and re-enga-
gement occurs at 4°C
Location:
Option1: The sensor is located in the air stream
where the air leaves the evaporator
Option2: The sensor is plugged on the evaporator’s
fins and located in the coldest area
Compressor cycling process
When the air temperature is below or equal to the
target value Tmin (about -1°C), the surface of the
evaporator may freeze.
The sensor detects this temperature and sends it to
the control system, which switches off the compres-
sor.
Tmax
A/C start up and cool down
Compressor cycling phase
Evaporator freezing
Time
Evaporator
temperature
Tmin
ON
OFF
OFF
ON
This causes a drop in the production of cold by the
evaporator and a gradual rise in the temperature on
its surface.
The sensor then detects this increase in the tempe-
rature and authorises the compressor to restart when
the temperature reaches Tmax.
A/C loops fitted with variable-cylinder and external
control compressors do not need an evaporator
sensor. The thermal power is adjusted in order to:
g
Avoid freezing on the evaporator
g
Provide greater comfort
g
Improve the efficiency of the system
g
Reduce the vehicle fuel consumption
Evaporator temperature
Evaporator freezing
OFF
ON
OFF
ON
Tmin (°C)
Tmax (°C)
61
+CLIM
F16
+ACC.
+BAT.
Cooling fan
A/C pressure sensing
Coolant temperature sensor
Compressor control
Fan high speed
Fan low speed