jcb JS300 Service Manual page 376

Air Conditioning System Operation
To maintain optimum operator comfort in warm climates or
during seasons of high ambient temperature, the air
conditioning system re-circulates, clean, dehumidified air
into the cab. Cooling is provided by passing the re-
circulated air, over an evaporator coil 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
E, condenser B, receiver drier D, expansion valve L and
A.K Fig 1. ( T
evaporator matrix
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 E, 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.
K Fig 1. ( T
B-4).
High pressure refrigerant is forced from the compressor to
the condenser B, which is mounted on the radiator on the
side 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 but with a lower heat
K Fig 1. ( T
content. B-4).
The refrigerant passes through the receiver drier D, which
contains a desiccant to remove moisture from the system.
K Fig 1. ( T
B-4).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 L, which
meters the amount of refrigerant entering the evaporator.
In the expansion valve the refrigerant instantaneously
expands to become a low pressure, low temperature
K Fig 1. ( T
liquid. B-4).
The refrigerant is drawn through the evaporator matrix A,
by the suction of the compressor. The temperature of
B-7
B-4).
9813/5100-1
Section B - Body and Framework
Heater/Air Conditioning SYSTEM
refrigerant is now considerably below that of the air being
drawn across the evaporator matrix by the blowers. Heat
is transferred from the ambient and re-circulated air to the
refrigerant, causing the low pressure liquid to vaporise and
become a low pressure gas. Moisture in the air condenses
on the evaporator matrix and is drained away via
K Fig 1. ( T
condensate. B-4).
Cool de-humidified air is emitted through air vents into the
cab.
The low temperature, low pressure, high heat content
refrigerant gas, is now drawn by suction back to the
compressor, where the cycle is completed.
Operation Overview
B-7