SECTION 50 -- CAB AIR CONDITIONING SYSTEM -- CHAPTER 1 27
603.54.471.00 -- 11 -- 2004
FUNCTION TESTING OF CAB AIR CONDITION-
ING SYSTEM (Op. 50 200 03)
With the pressure gauges connected to the system in
the manner described previously and the cocks
closed, proceed as follows:
1. Start the engine and bring it up to a speed of 1500
rpm.
2. Set the cab ventilation fan (1, fig. 9) to the maxi-
mum speed.
3. Turn knob (2, fig. 9) to switch on the air condition-
ing.
After about 15 minutes of operation, take the follow-
ing readings:
4. Pressure on suction side of compressor as indi-
cated by low pressure gauge.
5. Pressure on discharge side of compressor, as in-
dicated on high pressure gauge.
6. Ambient air temperature.
7. Ambient relative humidity.
8. Temperature of air leaving vents inside the cab.
The pressure values will depend on the external am-
bient conditions and the altitude.
The system is to be considered as functioning cor-
rectly if the pressure readings are within the value
ranges indicated on page 3, and the temperature
readings are within the value ranges indicated on
page 29.
9. Check also the temperature of the low and high
pressure sides of the system:
— the high pressure side, from the compressor dis-
charge to the expansion valve on the evaporator ,
should be uniformly hot to the touch;
— the low pressure side, from the evaporator outlet
to the suction side of the compressor, should be
uniformly cold to the touch. There should not be
excessive condensation on the suction pipe and
the low pressure pipe connector on the compres-
sor.
17
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10. Check that the compressor does not make un-
due noise; there should be an audible click when
the drive is engaged..
The sight glass on the receiver--drier can provide
useful information about system operation.
The four main possible conditions of the sight glass
are shown in figure 17.
A. Glass clear: indicates that the system is correctly
charged, or that there is no refrigerant in the system
( in the latter case the cooling action of the evaporator
would be absent). In some cases, the glass may be
clear when the system has been charged with an ex-
cessive quantity of refrigerant; in this case it would be
necessary to check the pressure readings.
B. Bubbles: the formation of vapour or foam
bubbles indicates that the system contains an insuffi-
cient quantity of refrigerant or the presence of air in
the system; bubbles may also be seen on switching
on the system and on disengagement of the electro-
magnetic clutch.
C. Threads of oil: indicates a lack of refrigerant and
that t he compressor oil is circulating the system.
D. Fluid appearance not uniform, streaky: indi-
cates that the drying agent in the filter has escaped,
as a result of the containment discs breaking, and is
circulating in the system.
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