Operating instructions

TM 11574A-OI
2-46
i. Temperature Control -- Frozen Mode.
With configuration variable CnF26 set to -10 C, the frozen mode of operation is active with
set points at or below +14 F (-10 C). With the variable set to +23 F (-5 C), the frozen mode is
active at or below +23 F (-5 C). When in the frozen mode, the controller maintains the return
air temperature at set point, the RETURN indicator light will be illuminated on the display
module, and the default reading on the display window will be the return air probe reading.
When the return air temperature enters the in-range temperature tolerance as selected at
function code Cd30, the in-range light will energize.
j. Frozen Mode -- Conventional.
Frozen range cargoes are not sensitive to minor temperature changes. The method of
temperature control employed in this range takes advantage of this fact to greatly improve the
energy efficiency of the unit. Temperature control in the frozen range is accomplished by
cycling the compressor on and off as the load demand requires. The unit will operate in the
conventional frozen mode when the controller set point is at or below the frozen range and
function code CD34 is set to “OFF.” If the return air temperature in the container drops 0.4 F
(0.2 C) below the set point, the compressor is cycled off. When the temperature is greater
than 0.4 F (0.2 C) above the set point and the three minute time delay has been met, the
compressor will restart. The unit will always operate at full capacity and the suction
modulation valve will open as allowed by current and pressure limiting.
NOTE
On start up of the unit, SMV will reset to a known open position. This is accomplished by
assuming the valve was fully open, driving it fully closed, resetting the percentage open
to zero, then opening to a known 21% staging position.
To prevent rapid cycling of the compressor, a three minute compressor off time must be satisfied
before the compressor will restart. Under a condition of rapidly changing return air temperature,
the time delay may allow the return air temperature to rise slightly above set point temperature
before the compressor can restart.
k. Frozen Mode -- Economy.
In order to activate economy frozen mode operation, a frozen set point temperature must be
selected. The economy mode is active when function code Cd34 is set to “ON.” When
economy mode frozen is active, the system will perform normal frozen mode operations
except that the entire refrigeration system, excluding the controller, will be turned off when
the control temperature is less than or equal to the set point 28.4 F (-2 C). After an off-cycle
period of 60minutes, the unit will turn on high speed evaporator fans for three minutes and
then check the control temperature. If the control temperature is greater than or equal to the
set point 32.6 F (0.2 C), the unit will restart the refrigeration system and continue to cool until
the previously mentioned off-cycle temperature criteria are met. If the control temperature is
less than the set point 32.6 F (0.2 C), the unit will turn off the evaporator fans and restart
another 60 minute off-cycle.