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When in the frozen mode the controller maintains the
return air temperature at set point, the RETURN
indicator light will be illuminated on the display module
and the default reading on the display window will be the
return air probe reading.
When the return air temperature enters the in-range
temperature tolerance as selected at function code
Cd30, the in-range light will energize.
3.3.13 Frozen Mode - - Conventional
Frozen range cargos are 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
accomplished by cycling the compressor on and off as
the load demand requires. The unit will operate in the
conventional frozen mode when the controller set point
is at or below the frozen range and function code CD34
is set to "OFF"
If the return air temperature in the container drops 0.2_C
(0.4_F) below the set point, 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 suction
modulation valve will open as allowed by current and
pressure limiting.
On start up of the unit, SMV will reset to a known
open position. This is accomplished by assum-
ing the valve was fully open, driving it fully
closed, resetting the percentage open to zero,
then opening to a known 21% staging position.
To prevent rapid cycling of the compressor, 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 above set
point temperature before the compressor can restart.
3.3.14 Frozen Mode - - Economy
In order to activate economy frozen mode operation, a
frozen set point temperature must be selected. The
economy mode is active when function code Cd34 is set
to "ON". 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.
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.
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3.4 CONTROLLER ALARMS
Alarm display is an independent controller software
function. If an operating parameter is outside of
expected range or a components does not return the
correct signals back to the controller an alarm is
generated. A listing of the alarms is provided in
Table 3-6, page 3-18.
The alarm philosophy balances the protection of the
refrigeration unit and that of the refrigerated cargo. The
action taken when an error is detected always considers
the survival of the cargo. Rechecks are made to confirm
that an error actually exists.
Some alarms requiring compressor shutdown have
time delays before and after to try to keep the
compressor on line. An example is alarm code "LO",
range
is
(low main voltage), when a voltage drop of over 25%
occurs, an indication is given on the display, but the unit
will continue to run.
An alarm is indicated by flashing an alarm code on the
display panel, and for some alarms, by the alarm light
illuminating.
When an Alarm Occurs:
a. The red alarm light will illuminate for "20 series"
alarms, and alarm code number AL55.
b. If a detectable problem is found to exist, its alarm
code will be alternately displayed with the set point on
the left display.
c. The user should scroll through the alarm list to deter-
mine what alarms exist or have existed. Alarms must
be diagnosed and corrected before the Alarm List can
be cleared.
To Display Alarm Codes :
a. While in the Default Display mode, press the ALARM
LIST key. This accesses the Alarm List Display Mode,
which displays any alarms archived in the Alarm
Queue.
b. The alarm queue stores up to 16 alarms in the se-
quence in which they occurred. The user may scroll
through the list by depressing an ARROW key.
c. The left display will show "AL##," where ## is the
alarm number sequentially in the queue.
d. The right display will show the actual alarm code.
"AA##" will display for an active alarm, where "##" is
the alarm code. Or "IA##" will display for an inactive
alarm, See Table 3-6, page 3-18,
e. "END" is displayed to indicate the end of the alarm list
if any alarms are active.
f. "CLEAr" is displayed if all alarms are inactive. The
alarm queue may than be cleared by pressing the EN-
TER key. The alarm list will clear and " -- -- -- -- -- " will
be displayed.
3.5. UNIT PRE-TRIP DIAGNOSTICS
Pre--Trip Diagnostics is an independent controller
function which will suspend normal refrigeration
controller activities and provide preprogrammed test
routines. The test routines include Auto Mode testing,
which automatically preforms a pre programmed
sequenced of tests, or Manual Mode testing, which
3-6
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