DCE80-100E
Technical Handbook
Air conditioning unit
Description
13
P.Group 10
TDCE01
04GB
Compressor
The air conditioning system is driven by the compressor. This
performs as a pump, drawing cold, low-pressure gas from the
evaporator, compressing it and thereby raising its temperature,
and discharging it at high pressure to the condenser.
The compressor is driven by V-belts directly from the diesel en-
gine. Switching between operation and idling is controlled by an
electro-magnetic clutch which, in turn, is controlled by a thermo-
stat whose sensor is located between the fins of the evaporator
coil. The thermostat switches off the compressor at low tempera-
tures, to prevent icing of the evaporator.
Condenser
The function of the condenser is to convert the hot high-pressure
gas from the compressor into liquid form. The tubes and fins of
the condenser coil absorb heat, which is then removed by the air
delivered by the fan.
The temperature of the refrigerant in the condenser varies from
about +50°C to +70°C. The pressure varies between 12 and 20
bar, depending on the ambient temperature and the flow of air
through the condenser. When the refrigerant is condensed into
liquid form, it is transferred under pressure to the liquid receiver/
filter dryer.
Liquid receiver with filter-dryer
The function of the liquid receiver with integrated filter dryer is to
collect the liquid coolant, bind the moisture, and to filter and re-
move impurities. The receiver, which is located in the condenser
housing, also serves as the expansion vessel in the refrigeration
circuit.
After flowing through the dryer in the bottom of the liquid receiver,
the refrigerant flows through a riser tube. A sight glass enables
the operator to check that the liquid flows without the presence of
any bubbles, and that the system is filled with a sufficient amount
of refrigerant.
Expansion valve
The expansion valve throttles the flow and passes an optimised
quantity of refrigerant that the evaporator is capable of evaporat-
ing.
The expansion valve is also the part of the circuit which separates
the high- pressure side from the low-pressure side. The refriger-
ant flows to the expansion valve under high pressure and leaves
it under low pressure.
The amount of refrigerant which passes the evaporator varies,
depending on the thermal load. The valve operates from ’fully
open’ to ’fully closed’ and in-between searches for a point to give
optimum evaporation.
Evaporator
The heat necessary for evaporating the refrigerant is extracted
from the cab air which is circulated by a fan through the evapora-
tor coil. The cab air is thus cooled, and is distributed and returned
to the cab.
In the evaporator, the refrigerant reverts to the gaseous state and
returns to the compressor suction, thereby completing the cycle.
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