62-61753-21
Switch On when CT-SP
is greater than or equal
to 0.2°C (0.36°F)
Switch Off when CT-SP
is less than -0.2°C
(0.36°F)
Between Cool & Heat or Heat & Cool
Switch On when CT-SP
is equal to or less than -
0.3°C (-0.54°F)
Switch Off when CT-SP
is greater than -0.2°C
(0.36°F)
When Null Mode is required and the system is operat-
ing in:
Engine/Start-Stop Operation, the engine & refriger-
ation system (compressor, condenser fans and
evaporator fans) will shut down if the remaining
Stop Parameters have been satisfied.
Standby/Start-Stop Operation, the refrigeration
system will shut down if the remaining Stop Param-
eters have been satisfied.
Engine/Continuous Operation, the compressor will
shut down while the engine and evaporator fans
will continue to operate. The condenser fan will op-
erate if engine cooling is required.
Standby Continuous Operation, the compressor
and condenser fans will shut down while the evapo-
rator fans will continue to operate.
4.5.3 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 descriptions of operation when cooling, with
flow diagrams, refer to section 2.14.
Pulldown
Pulldown will be entered:
following a Start-Up.
following a Setpoint change (requiring additional
cooling).
following an operational change (Start-Stop vs
Continuous or Engine Operation vs Standby Op-
eration).
following a defrost termination.
or when all other Stop Parameters have been met
except the refrigerated compartment Temperature
Stop Parameter.
Pulldown will end when one of the following occurs:
when in Engine Operation and the microprocessor
is calling for low speed.
when in Start-Stop and the refrigerated compart-
ment Temperature Stop Parameter has been satis-
fied while one or more of the other Stop Parame-
ters has not.
when in Continuous Operation, with a setpoint less
than 18.4°C (65.1°F) and the microprocessor has
calculated Control Temperature is in the required
range.
This range is calculated when Supply Temperature
(ST) is equal to or less than the Return Tempera-
ture (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.
CSMV Control
CSMV Control will be entered when additional cooling
is required and Pulldown is not allowed. In CSMV Con-
trol the valve will be modulated so as to balance com-
pressor capacity with the refrigeration load.
4.5.4 Heat Mode
When Heat Mode is required the system will operate
with the evaporator fans energized. Operation of the
heaters is determined in accordance with the calculat-
ed Controlling Temperature value (CT) and the differ-
ence between this value and Setpoint (SP) in accord-
ance with the following:
Switch On when CT-SP
is less than -0.3°C
(-0.54°F)
Switch Off when CT-SP
is greater than -0.2°C
(-0.36°F)
Switch On when CT-SP
is less than -0.2°C
(-0.36°F)
Switch Off when CT-SP
is greater than -1.8°C
(-3.24°F)
HTCON1 may also be activated when the unit is in
Continuous Operation Cooling to assist in balancing
unit capacity with the load. In all other operating states
and modes HTCON1 and HTCON2 will not be activat-
ed.
4.5.5 Null Mode
For descriptions of operation in the Null Mode, refer to
4.5.2.
4.5.6 Defrost Mode
Defrost is an independent cycle overriding cooling and
heating functions in order to de-ice the evaporator.
When the unit is in defrost, the DEFROST LED will be
on, the MessageCenter will display DEFROST CYCLE
STARTED for 5 seconds. The center of the Main Dis-
play will show "dF". Defrost will not be allowed until the
DDT is below 4.4°C (40.0°F).
1. Defrost Initiation And Start
Defrost can be initiated by pressing the MANUAL DE-
FROST key or automatically by the microprocessor.
Microprocessor initiation is based on coil condition or
expiration of the defrost timer.
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