Unit Description
23
speed windings is energized and the evaporator
fans run at approximately 1800 rpm. This keeps
the evaporator air flow consistent regardless of the
engine speed. In certain cases when the engine is
running in low speed, the evaporator fan contactor
connected to the low speed windings is energized
and the evaporator fans run at approximately 1180
rpm.
Figure 4: Front View Showing Evaporator Fans
Through Access Panel
Refrigeration Cluster
Most of the refrigeration system components are
located in the refrigeration cluster on the lower
curbside of the unit. This allows good access from
the front and side for maintenance, diagnosis, and
repair.
Figure 5: Front View of Refrigeration Cluster
Thermo King X430L Reciprocating
Compressor
The unit is equipped with a Thermo King X430L
reciprocating compressor with 30.0 cu. in.
(492 cm
3
) displacement.
Electronic Throttling Valve
The Electronic Throttling Valve (ETV) is a
variable position valve operated by a stepper
motor. The ETV is located in the suction line
between the accumulator and the suction
vibrasorber. Discharge and suction pressure
transducers supply pressure information to the
microprocessor control system. The
microprocessor controls the electronic throttling
valve directly. The ETV replaces the mechanical
throttling valve used in other units.
The ETV system provides enhanced control of the
refrigeration system as follows:
Suction Pressure Control:
The suction pressure
control algorithm is the primary control used to
obtain maximum capacity. This allows the
refrigeration system to fully utilize the power
capabilities of the engine under varying
conditions.
Discharge Pressure Protection:
This protection
algorithm provides an additional measure of
protection against high discharge pressures and
possible compressor damage. It will prevent
shutdowns in high ambient temperatures by
allowing continued operation of the unit at a
temporarily reduced refrigeration capacity.
Engine Coolant Temperature Protection:
This
protection algorithm protects the engine from high
coolant temperature shutdowns and possible
engine damage. It will reduce the load on the
engine by temporarily reducing refrigeration
capacity. This lowers the engine temperature
while still allowing continued unit operation.
Modulation Control:
Modulation control provides
precise control of the temperature in the cargo
area. As the return air temperature begins to
approach the setpoint, the microprocessor begins
to close the ETV to reduce the capacity. The
microprocessor closes the ETV more as the return
air temperature gets closer to the setpoint. When
the return air temperature is near setpoint, the
ETV may close to its limit and the hot gas bypass
ARA1974
