SECTION 50 -- CAB AIR CONDITIONING SYSTEM -- CHAPTER 1 17
603.54.471.00 -- 11 -- 2004
12
Thermostatic expansion valve
Serves to reduce the pressure of the refrigerant as it
enters the evaporator so that it can change state and
thus remove heat from the surrounding air .
The expansion valve performs two basic functions:
— metering: the calibrated orifice (6, fig. 12) in the
valve body creates a dif ference in the pressure of
the refrigerant at the inlet (4) (liquid state) and the
outlet (7) (mixed liquid/vapour); the calibrated
orifice (6) also serves to atomise the refrigerant
to facilitate subsequent evaporation;
— modulation: inside the valve body a thermostatic
sensor controls the valve aperture so that the
right quantity of refrigerant enters the evaporator
to ensure complete evaporation.
If the thermostatic sensor (2, fig. 12) detects an in-
crease in the cab temperature, the flow of refrigerant
is increased.
A drop in the temperature or an increase in the com-
pressor capacity (due to an increase in the engine
speed) will cause a reduction in the flow of refrigerant
into the evaporator .
The expansion valve is installed on the evaporator in-
let fitting (7), and as the internal refrigerant flow con-
trol system is completely automatic, it requires no
special maintenance.
To perform functional testing, with the system is fully
charged, check that the system operating pressures
are those indicated on page 3.
Expansion valve block.
1. From evaporator outlet.
2. Thermostatic sensor.
3. To compressor suction inlet.
4. From receiver--drier.
5. Spring.
6. Calibrated orifice and ball.
7. To evaporator inlet.
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2
3
4
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7
Note -- In case of malfunction, replace the valve.
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