R-134a Refrigerant
Due to environmental concerns, the use of ozone depleting
chlorofluorocarbons (CFCs) in air conditioning systems is
being gradually phased out.
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The R-12 refrigerant used in some systems contains CFCs
and is now being replaced by a hydrofluorocarbon (HFC)
refrigerant R-134a, which does not cause ozone depletion.
The refrigerant used in the 3CX air conditioning system
is R-134a.
Air conditioning systems using R-134a refrigerant are not
compatible with systems using R-12 refrigerant. No attempt
should be made to charge R-134a systems with R-12
refrigerant.
System Operation
To maintain optimum operator comfort in warm climates or
during seasons of high ambient temperature, the air
conditioning system delivers cool, dehumidified air into the
cab. Cooling is provided by passing the warm ambient air,
together with recirculated air, over an evaporator matrix in
the air conditioning unit.
The air conditioning system is a closed circuit through which
the refrigerant is circulated, its state changing from gas to
liquid and back to gas again, as it is forced through the
system.
The major components of the system are the compressor A,
condenser matrix B, receiver drier C, expansion valve D and
evaporator matrix E.
To operate the air conditioning, press switch F to switch the
system on. Press switch G to operate the 3-speed heater
fan. Rotate H to select the desired temperature. Control J
enables the operator to select either recirculating air or fresh
air from outside the machine. A combination of both is also
obtainable.
Air conditioning system power is generated from the engine,
via an electromagnetic clutch to the compressor. Three
switches, connected in series, are included in the clutch
supply line, all must be closed for the clutch and therefore
the air conditioning system to operate.
The compressor A draws in low pressure refrigerant gas
from the suction line (evaporator to compressor) and
increases refrigerant pressure through compression. This
process also increases the refrigerant temperature.
High pressure refrigerant is forced from the compressor to
the condenser B, which is mounted at the front of the
engine. Ambient air is drawn across the condenser by the
engine- driven cooling fan. In the condenser, the refrigerant
changes state to a high pressure, high temperature liquid
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but with a lower heat content.
The refrigerant passes through the receiver drier C, which
contains a desiccant to remove moisture from the system.
The receiver drier serves as a reservoir for refrigerant and
also includes a filter to remove foreign particles from the
system.
The high temperature, high pressure refrigerant is forced by
compressor action into the expansion valve D, which meters
the amount of refrigerant entering the evaporator. In the
expansion valve the refrigerant instantaneously expands to
become a low pressure, low temperature liquid.
