Service manual

T -318
3-- 6
additional capability of selecting dehumidification set
points from 60 to 95% (instead of the normal 65 to 95%).
In addition, if bulb mode is active, function code Cd37
may be set to override the previous defrost termination
thermostat settings (refer to paragraph 4.10.4) The
temperature at which the defrost termination thermostat
will be considered “open” may be changed [in 0.1
degrees C (0.2 degrees F) increments] to any value
between 25.6 C (78 F) and 4 C (39.2 F). The
temperature at which the defrost termination thermostat
is considered closed for interval timer start or demand
defrost is 10 C (50 F) for “open” values from 25.6 C down
to a 10 C setting. For “open” values lower than 10 C, the
“closed” values will decrease to the same value as the
“open” setting.
Bulb mode is terminated when:
1. Bulb mode code Cd35 is set to “Nor.”
2. Dehumidification code Cd33 is set to “Off.”
3. The user changes the set point to one
that is in the frozen range.
When bulb mode is disabled by any of the above, the
evaporator fan operation for dehumidification reverts to
“alt” and the DTS termination setting resets to the value
determined by controller configuration variable CnF41.
3.3.12 Temperature Control -- Frozen Mode
With configuration variable CnF26 set to -10 C, the
frozen mode of operation is active with set points at or
below -10 C (+14 F). With the variable set to -5 C, the
frozen mode is active at or below -5 C (+23 F).
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 cargoes 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 control in the frozen range is
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
degrees C (0.4 degrees F) below the set point, the
compressor is cycled off. When the temperature is
greater than 0.2 degrees C (0.4 degrees 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.
NOTE
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 refrigerat ion system, excluding
the controller , will be turned off when the control
temperature is less than or equal to the set point
-2 degrees 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 degrees C, the unit will restart the
refrigeration syst em 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 degrees C, the unit will turn off the evaporator fans
and restart another 60 minute of f-cycle.
3.4 CONTROLLER ALARMS
Alarm display is an independent controller software
function. If an operating parameter is outside of
expected range or a component 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,”
(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.
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.