62-11785 4–6
4.6.3 Cool/Heat/Null Mode Switching Logic
When not in Pulldown and in Continuous Run Mode, operation in cool, heat and null modes is determined in accor-
dance with the calculated Controlling Temperature value (CT), the difference between this value and Setpoint (SP)
and the FUEL SAVER (ECO) MODE Functional Parameter setting in accordance with:
When Null Mode is required and the system is operating in Standby Continuous Operation, the compressor and
condenser fans will shut down while the evaporator fan continues to operate.
In Continuous Run, when difference between ambient and setpoint is <10°C, the COMPRESSOR
RESTART OFFSET configuration value will be used for the switch point to turn cool on (instead of
0.2°C). If ambient and setpoint are more than 10°C then the switch point remains 0.2°C.
4.6.4 Cool Mode
When Cool Mode is required the system will operate in Pulldown or CSMV Control. Pulldown operation will include
periods of time in Economized Mode and Standard Mode. CSMV control will occur in Standard Mode. For descrip-
tions of operation when cooling, with flow diagrams, refer to Section 2.12.
Pulldown:
Pulldown will be entered:
• following a Start-Up
• following a Setpoint change (requiring additional cooling)
• following a defrost termination
• or when all other Stop Parameters have been met except compartment Temperature Stop Parameter
Pulldown will end when one of the following occurs:
• In Start-Stop and the compartment Temperature Stop Parameter has been satisfied while one or more of the
other Stop Parameters has not
• In Continuous Operation - perishable and temperature is in required range. This range is calculated when Supply
Temperature (ST) is equal to or less than Return Temperature (RT). The calculation is:
Off Value = ST - RT/2
When the Control Temperature is within a range of ± the Off Value of set point, Pulldown Mode ends.
• If in Continuous Operation - Perishable, and the High Speed Pulldown Configuration is ON: when the tem-
perature is equal to setpoint.
• when active probe is within the control temperature which allows the unit to shut off.
CSMV Control:
CSMV Control will be entered when additional cooling is required and Pulldown is not allowed. In CSMV Control
the valve will be modulated so as to balance compressor capacity with the refrigeration load.
Control Temperature with Fuel Saver OFF
COOL MODE
Switch On when CT-SP is greater than or equal to 0.36°F
(0.2°C)
Switch Off when CT-SP is less than -0.36°F (-0.2°C)
NULL MODE
Between Cool & Heat or Heat & Cool
HEAT MODE
Switch On when CT-SP is equal to or less than -0.54°F
(-0.3°C)
Switch Off when CT-SP is greater than 0.36°F (0.2°C)
Control Temperature with Fuel Saver ON
COOL MODE
Switch On when CT-SP is greater than or equal to the
S/S OVERRIDE Functional parameter.
Switch Off when CT-SP is less than -0.32°F (-0.0°C)
NULL MODE
Between Cool & Heat or Heat & Cool
HEAT MODE
Switch On when CT-SP is equal to or less than -1.44°F
(-0.8°C)
Switch Off when CT-SP is greater than 1.26°F (0.7°C)
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