Carrier 69NT40-541-500 Operation And Service Manual
Also see for 69NT40-541-300: Operation and service
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Contents
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4–11 T-363After an off-cycle period of 60 minutes, the unit will turn on high speed evaporator fans for three minutes and thencheck the control temperature. If the control temperature is greater than or equal to the frozen set point +0.2°C(0.36°F), the unit will restart the refrigeration system and continue to cool until the previously mentioned off-cycletemperature criteria are met. If the control temperature is less than the frozen set point +0.2°C (0.36°F), the unit willturn off the evaporator fans and restart another 60 minute off-cycle.4.3.16 Frozen Mode Cooling - Sequence of OperationNOTES1. In the Frozen Mode the evaporator motors run in low speed.2. In low temperature ambients, the condenser fan will be cycled by the controller to maintain propercondensing pressure, refer to Section 4.4.4.a. When the return air temperature is above set point and decreasing, the unit will be cooling with the con-denser fan motor (CF), compressor motor (CH), evaporator fan motors (ES) energized and the white COOLlight illuminated (see Figure 4.9).b. When the return air temperature decreases to a predetermined tolerance above set point, the greenINRANGE light is illuminated.c. When the return air temperature decreases to 0.2°C (0.36°F) below set point, contacts TC and TN are openedto de-energize the compressor and condenser fan motors. The white COOL light is also de-energized.d. The evaporator fan motors continue to run in low speed to circulate air throughout the container.e. The green IN-RANGE light remains illuminated as long as the return air is within tolerance of set point.f. When the return air temperature increases to 0.2°C (0.36°F) above set point and the three minute off time haselapsed, relays TC and TN are energized to restart the compressor and condenser fan motors. The white COOL lightis also illuminated.Figure 4.9 Frozen Mode4.3.17 DefrostDefrost is initiated to remove ice buildup from the evaporator coil which can obstruct air flow and reduce the coolingcapacity of the unit. The defrost cycle may consist of up to three distinct operations depending upon the reason forthe defrost or model number configuration. The first is de-icing of the coil, the second is defrost due to a probecheck cycle and the third is a snap freeze process based on the unit model configuration.Defrosting the coil consists of removing power to the cooling components (compressor, evaporator fans, andcondenser fan), closing the SMV, and turning on the heaters, which are located below the evaporator coil.During normal operation, de-icing will continue until temperatures indicate that the ice on the coil has beenremoved, proper air flow has been restored, and the unit is ready to control temperature efficiently.CONTROL TRANSFORMERPOWER TOCONTROLLERSIGNAL TOCONTROLLERSIGNAL TOCONTROLLERENERGIZEDDE-ENERGIZEDFOR FULL DIAGRAM ANDLEGEND, SEE SECTION 7 |
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