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out-of-range or compressor shutdown condition, the
heat relay is de-energized immediately.
The out-of-range timer is provided to allow the heaters
to remain energized during a temporary out-of-range
condition. If the control probe 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 function code Cd30.
Cooling capacity reduction by modulation is the same
as described for the conventional operating mode when
any of the above first four conditions (1. thru 4.) are
invalid.
With set points below - -10_C (+14_F), or - -5_C
(+23_F) optionally, heating and dehumidification are
locked out.
c. Operation in the economy mode
(Code 34 set to ON)
The economy mode selection determines the status of
the economy mode of operation. There are two values:
"ON" and "OFF." A code which represents the status of
this function is recorded in the DataCorder memory
whenever the value is changed.
Economy mode is a user selectable mode of operation
provided for power saving purposes. Economy mode
could be utilized in the transportation of temperature
tolerant cargo or non-respiration items which do not
require high airflow for removing respiration heat.
The economy mode is activated by selecting function
code Cd34 to the "ON" status. There is no active display
indicator that economy mode has been activated, and a
manual display of Cd34 is a way to be sure if the
economy mode is or is not active.
In order to achieve economy mode perishable operation,
a perishable set point must be selected PRIOR to
activating economy mode. When economy mode
perishable is active, the evaporator fans will be
controlled as follows: At the start of each cooling or
heating cycle, the high speed evaporator fans will be run
for three minutes. After that initial three minutes, the
evaporator fans will be switched to low speed any time
the supply air temperature is within ¦ 0.25_C (0.45_F)
of the set point and the return air temperature is less than
or equal to the supply air temperature + 3_C (5.4_F).
When the fans switch to low speed, they will run in low
speed for one hour. At the end of the hour, the
evaporator fans will switch back to high speed. The
evaporator fans will again run in high speed for three
T-268-07
minutes and the above mentioned cycle will be
repeated, just as it was from the start of the cooling or
heating cycle. If the unit is not equipped with dual speed
evaporator fans, then economy mode perishable will
perform exactly the same as the normal control mode.
d. Operation in bulb mode (Code 35 set to bulb and
Code 33 selected)
Bulb mode is an extension of the dehumidification
mode. Dehumidification must be enabled by selecting a
value (percentage of relative humidity) at function code
Cd33 before bulb mode function code Cd35 can be
initiated.
To initiate bulb mode, use the ARROW keys to scroll to
function code Cd35 and change from "Nor" to "bulb."
Once the bulb mode is activated, the user may then
change from the normal evaporator fan operation where
the fan speed alternates every hour between low or high
speed operation. This is done by toggling function code
Cd36 from its default of "alt" to "Lo" or "Hi"
respectively. If low speed evaporator fan operation is
selected, this gives the user 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, the user is given the
option to change the defrost termination sensor (DTS)
temperature, in which defrost is terminated from the
normal 25.6_C (78_F) temperature setting to 4_C
(39.2_F) in 0.1_C (0.2_F) increments. The temperature
set point that the DTS temperature must go below
before the defrost interval timer begins counting down
also changes from 0_C to 10_C as the desired DTS
termination temperature is raised.
Bulb mode is terminated when:
Code Cd35 is set to "Nor."
S
Code Cd33 for dehumidification is set to
S
"Off."
The user changes the set point to one
S
that is in the frozen range.
When bulb mode is disabled by any of the above means,
the evaporator fan operation for dehumidification
reverts to "alt" and the DTS termination setting resets to
the normal 25.6_C (78_F).
3-16
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