Carrier 69NT40-541-306 Operation And Service
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T-354 4–8Bulb mode is terminated when:1. Bulb mode code Cd35 is set to “Nor”.2. Dehumidification code Cd33 is set to "Off".3. The user changes the set point to one that is in the frozen range.When bulb mode is disabled by any of the above, the evaporator fan operation for dehumidification reverts to "alt"and the DTS termination setting resets to the value determined by controller configuration variable CnF41.4.3.12 Temperature Control - Frozen ModeWith configuration variable CnF26 set to -10C, the frozen mode of operation is active with set points at or below -10C (+14F). With the variable set to -5C, the frozen mode is active at or below -5C (+23F).When in the frozen mode, the controller maintains the return air temperature at set point, the RETURN indicatorlight will be illuminated on the display module, and the default reading on the display window will be the return airprobe reading.When the return air temperature enters the in-range temperature tolerance as selected at function code Cd30, thein-range light will energize.4.3.13 Frozen Mode - ConventionalFrozen range cargoes are not sensitive to minor temperature changes. The method of temperature controlemployed in this range takes advantage of this fact to greatly improve the energy efficiency of the unit. Tempera-ture 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 rangeand function code CD34 is set to "OFF."If the return air temperature in the container drops 0.2C (0.4F) below the set point, the compressor is cycled off.When the temperature is greater than 0.2C (0.4F) above the set point and the three minute time delay has beenmet, the compressor will restart. The unit will always operate at full capacity and the suction modulation valve willopen as allowed by current and pressure limiting.NOTEOn start up of the unit, SMV will reset to a known open position. This is accomplished by assuming thevalve was fully open, driving it fully closed, resetting the percentage open to zero, then opening to aknown 21% staging position.To prevent rapid cycling of the compressor, a three minute compressor off time must be satisfied before the com-pressor will restart. Under a condition of rapidly changing return air temperature, the time delay may allow thereturn air temperature to rise slightly above set point temperature before the compressor can restart.4.3.14 Frozen Mode - EconomyIn order to activate economy frozen mode operation, a frozen set point temperature must be selected. The economymode is active when function code Cd34 is set to “ON”. When economy mode frozen is active, the system will per-form normal frozen mode operations except that the entire refrigeration system, excluding the controller, will beturned off when the control temperature is less than or equal to the set point -2C. After an off-cycle period of 60 min-utes, the unit will turn on high speed evaporator fans for three minutes and then check the control temperature. If thecontrol temperature is greater than or equal to the set point +0.2C, the unit will restart the refrigeration system andcontinue to cool until the previously mentioned off-cycle temperature criteria are met. If the control temperature is lessthan the set point +0.2C, the unit will turn off the evaporator fans and restart another 60 minute off-cycle.4.4 CONTROLLER ALARMSAlarm display is an independent controller software function. If an operating parameter is outside of expectedrange or a component does not return the correct signals back to the controller, an alarm is generated. A listing ofthe alarms is provided in Table 4–6.The alarm philosophy balances the protection of the refrigeration unit and that of the refrigerated cargo. The actiontaken when an error is detected always considers the survival of the cargo. Rechecks are made to confirm that anerror actually exists. |
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