3-17
T-294-01
3.1.7.2 Frozen Range Below --10
_
_
_
_
C (+14
_
_
_
_
F), or
--5
_
_
_
_
C (+23
_
_
_
_
F) Optionally
For set points
below
--10
_
C (+14
_
F), or --5
_
C (+23
_
F)
optionally, the Controller maintains RETURN air at the
set point temperature using the following modes of
operation:
a. Operation in the conventional mode
(Code 33 OFF)
The return air probe is used for control and is so
indicated by the LED on the display board.
The Frozen temperature range is not sensitive to minor
temperature changes. The method of temperature
control employed in this range takes advantage of this
fact to greatly improve the energy efficiency of the unit.
Temperature control in the Frozen range
at or below
--10
_
C (+14
_
F),
or --5
_
C (+23
_
F) optionally, is
accomplished by cycling the compressor on and off as
the load demand requires.
If the return air temperature in the container drops 0.2
_
C
(0.4
_
F) below the set point temperature, the compressor
is cycled off. When the temperature is greater than
0.2
_
C (0.4
_
F) above the set point and the three minute
time delay has been met, the compressor will restart.
The unit will always operate at full capacity, and the
stepper motor suction modulation valve (SMV) will
open to 100%, or as allowed by current and pressure
limiting.
NOTE
On start up of the unit, SMV will reset to a
known open position. This is accomplished by
assuming the valve was fully open, driving it
fully closed, resetting the percentage open to
zero, then opening to a known 21% staging
position. This makes the unit ready to start and
normal operation will begin.
To prevent on/off cycling of the compressor from
occurring, a three minute compressor off time must be
satisfied before the compressor will restart. Under a
condition of rapidly changing return air temperature,
the time delay may allow the return air temperature to
rise slightly more than 0.2
_
C (0.4
_
F) above the set
point temperature before the compressor can restart.
b. Operation in the economy mode (Code 34 OFF)
The economy mode is deactivated by setting function
code Cd34 to the “OFF” status. Economy mode has no
active display indicator to show that it is enabled, so a
manual display of function code Cd34 must be
performed to enable the user to see its current status. A
second way to deactivate economy mode is to change
the set point. Once economy mode is deactivated, the
system will return to normal control mode operations.
In order to achieve economy mode frozen operation, a
frozen set point temperature must be selected PRIOR to
activating economy mode. When economy mode frozen
is active, the system will perform normal frozen mode
operations except that the entire refrigeration system,
excluding the Controller, will be turned off when the
control temperature is less than or equal to the set point --
2
_
C, (i.e., the set point is set at --11
_
C and the operator
subtracts --2
_
C, the result will equal --13
_
C). After an
off-cycle period of 60 minutes, the unit will turn on high
speed evaporator fans for three minutes, and then check
the control temperature. If the control temperature is
greater than or equal to the set point + 0.2
_
C., the unit
will restart the refrigeration system and continue to cool
until the previously mentioned off-cycle temperature
criteria are met. If the control temperature is less than
the set point + 0.2
_
C, the unit will turn off the
evaporator fans and restart another 60 minute off-cycle.
c. Operation in the bulb mode (Code 35 OFF)
The unit will not run in bulb mode if a frozen range set
point is selected. As described in section 3.1.7.1.d., if a
frozen set point is selected, dehumidification is
deactivated and the temperature above which DTS must
go during defrost resets to 25.6
_
C (78
_
F).
3.2 PRE-TRIP DIAGNOSTICS
CAUTION
Pre-trip inspection should not be performed
with critical temperature cargoes in the
container.
NOTE
When Pre-Trip is initiated, dehumidification
and bulb mode will be deactivated. At the
completion of Pre-Trip, dehumidification and
bulb mode must be turned back on again.
Pre-trip Diagnostics is an independent mode which will
suspend the normal Control Mode activities when
initiated by the user. With pre-trip diagnostics, either all
the pre-trip tests can be executed in a defined sequence
(Auto Mode), or one of the pre-trip tests can be selected
to be executed (Manual Mode), based on the sequence
of key selections made.
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