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EN
Passport I/O Digital Controls Operation
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To provide heat when the required water
temperature is not available, install the optional
electric heater, and program parameter P-19.
See “Programming the Passport Control” on
page 16.
7 .1 .3 Air and Water Temperature
Differential (CW Systems Only)
The electric heater and the chilled-water heat can affect
the CW system.
The optional electric heater overlaps with the chilled-
water heat by 22 °F (12° C). The heater turns on
when required and remains on until the chilled-water
temperature exceeds the ambient air temperature by
22 °F (12° C) or until the room temperature is satisfied.
During very cold conditions, the electric heat overlaps
the chilled-water heat to supplement heating.
Water Temperature
Differential in °F
Default is 15 °F (-9 °C)
Valve
Electric
Heater
22 °F (-6 °C)
Open
Off
15 °F (-9 °C)
Open
On
7 to 15 °F (-14 to 9 °C)
Hysteresis
On
7 °F (-14 °C)
Close
On
7 to 0 °F (-14 to -18 °C)
Close
On
0 °F (-18 °C)
Close
Off
0 to -7 °F (-18 to -22 °C)
Close
Off
-7 °F (-22 °C)
Close
Off
-7 to -15 °F (-22 to -26 °C)
Hysteresis
Off
-15 °F (-26 °C)
Open
Off
7 .1 .4 Reversing-Valve Operation
(DX Systems Only)
The position of the reversing valve determines COOL
mode or HEAT mode. The reversing valve automatically
toggles between HEAT and COOL in these situations:
• When the system runs in either the HEAT mode or
COOL mode and the opposite cycle is needed to
maintain the temperature, the reversing valve toggles
to the opposite position to initiate the opposite cycle
and reduce the starting surge of the compressor.
• When a cooling or heating cycle initiates after the
system has been OFF for less than 75 seconds
(5 minutes for Passport control displays with firmware
B30 or newer).
• When interrupting a cycle by pressing the
Power
button on the display or changing the set point using
the display panel.
To reduce reversing-valve noise, the default limits
unnecessary valve toggling. Program the minimum
compressor staging delay (parameter P-4) to 75 seconds
or greater (5 minutes for Passport control displays with
firmware B30 or newer), to eliminate valve toggling. See
“Programming the Passport Control” on page 16.
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When the system is powered up, a power-on-reset
always initiates a valve toggle.
7 .1 .5 De-icing Cycle (DX Systems Only)
DX systems have a de-icing cycle option to prevent ice
buildup on the evaporator coil during extended periods
of cooling operation. Installation variables, such as
grille sizes, length of ducting, insulation, and ambient
temperatures, determine the runtime required to achieve
the set point.
Factors that substantially increase the runtime include
operating the system with hatches and doors open
and programming an unrealistic set point (for example,
65 °F/18 °C). Such situations can cause the evaporator to
form ice on warm humid days.
Based on your software version and parameter settings,
de-icing occurs in one of two ways:
• For software version A21 and newer: by monitoring
the room air temperature in 10-minute intervals during
a cooling cycle. Depending on the parameter value
and the change in room temperature during these
monitoring intervals, the Passport control initiates
short compressor shutdown periods combined with
a one-speed increase in the fan speed and a periodic
HEAT mode cycle with the fan turned off.
• For software version A13 and older: by switching the
reversing valve into HEAT mode while the system
is cooling. The valve remains energized for the
programmed cycle time.
For additional details on parameter settings, see
“Selecting a Parameter” on page 17.
