Perishable, Dehumidification − Bulb Mode; Perishable Economy; Perishable Mode Cooling − Sequence Of Operation; Figure 4.6 Perishable Mode Cooling - Carrier 69NT40-541-505 Operation And Service Manual

Two timers are activated during dehumidification to
prevent rapid cycling and consequent contactor wear:
1. Heater debounce timer (three minutes) − The
heater debounce timer is started whenever the
heater contactor status is changed. The heat
contactor remains energized (or de-energized)
for at least three minutes even if the set point
criteria is satisfied.
2. Out-of-range timer (five minutes) − The out-of-
range timer is started to maintain heater opera-
tion during a temporary out-of-range condition. If
supply air temperature remains outside of the
user selected in-range setting for more than five
minutes, the heaters will be de-energized to
allow the system to recover. The out-of-range
timer starts as soon as the temperature exceeds
the in-range tolerance value set by Cd30.
4.3.7 Perishable, Dehumidification − Bulb Mode
Bulb mode is an extension of dehumidification which
allows changes to the evaporator fan speed and/or
defrost termination set points.
Bulb mode is active when Cd35 is set to "Bulb." Once
bulb mode is activated, the user may then change the
dehumidification mode evaporator fan operation from
the default (speed alternates from low to high each
hour) to constant low or constant high speed. This is
done by toggling Cd36 from its default of "alt" to "Lo" or
"Hi" as desired. If low speed evaporator fan operation
is selected, the user has the 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, Cd37 may be set to
override the previous defrost termination thermostat
(DTT) settings. The temperature at which the DTT will
be considered "open" may be changed [in 0.1°C
(0.2°F) increments] to any value between 25.6°C
(78°F) and 4°C (39.2°F). The temperature at which the
DTT is considered closed for interval timer start or
demand defrost is 10°C (50°F) for "open" values from
25.6°C (78°F) down to a 10°C (50°F) 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 CnF41.
4.3.8

Perishable Economy

Economy fan mode is an extension of the Perishable
Mode, and is provided for power saving purposes.
Economy fan mode is activated when Cd34 (also used
for Frozen Economy Mode) is set to "ON." Economy
fan mode is used in the transportation of temperature-
T-368
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tolerant cargo or non-respiration items which do not
require high airflow for removing respiration heat.
There is no active display that indicates that economy
fan mode has been initiated. To check for economy fan
mode, perform a manual display of Cd34.
In order to achieve economy mode, a perishable set
point must be selected prior to activation. When econ-
omy mode is active, the evaporator fans will be con-
trolled as follows:
At the start of each cooling or heating cycle, the evapo-
rator fans will run in high speed for three minutes.
After the initial three minutes, they will then be switched
to low speed any time supply air temperature is within
+/-0.25°C (0.45°F) of set point and return air tempera-
ture is less than or equal to supply air temperature
+3°C (5.4°F).
The fans will continue to run in low speed for one hour.
At the end of the hour, the evaporator fans will switch
back to high speed and the cycle will be repeated.
4.3.9 Perishable Mode Cooling − Sequence of
Operation
In Standard Perishable Mode, the evapora-
tor motors run in high speed. In Economy
Fan Mode, fan speed is varied.
In low temperature ambients, the condenser
fan will be cycled by the controller to main-
tain proper condensing pressure.
a. With supply air temperature above set point and
decreasing, the unit will cooling with the con-
denser fan motor (CF), compressor motor (CH),
evaporator fan motors (EF) energized, and the
white COOL light illuminated (see

Figure 4.6 Perishable Mode Cooling

ENERGIZED
DE ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER
NOTE: HIGH SPEED EVAPORATOR FAN SHOWN. FOR LOW SPEED
CONTACT TE IS DE-ENERGIZED AND CONTACT TV IS ENERGIZED
4–6
NOTE
NOTE
Figure 4.6).
CONTROL TRANSFORMER
SIGNAL TO
CONTROLLER