Carrier 69NT40-541-306 Operation And Service
                                                                                                                                                          | |
Contents
| 
4–7 T-3544.3.10 Perishable Mode - DehumidificationThe dehumidification mode is provided to reduce the humidity levels inside the container. The mode is activatedwhen a humidity value is set at function code Cd33. The display module SUPPLY LED will flash ON and OFF everysecond to indicate that the dehumidification mode is active. Once the mode is active and the following conditionsare satisfied, the controller will activate the heat relay to begin dehumidification.1. The humidity sensor reading is above the set point.2. The supply air temperature is less than 0.25C above set point.3. The heater debounce timer (three minutes) has timed out.4. Heater termination thermostat (HTT) is closed.If the above conditions remain true for at least one hour, the evaporator fans will switch from high to low speedoperation. The evaporator fan speed will switch every hour thereafter as long as all conditions are met (see BulbMode section for different evaporator fan speed options). If any condition except for item (1) becomes false OR ifthe relative humidity sensed is 2% below the dehumidification set point, the high speed evaporator fans will beenergized.In the dehumidification mode, power is applied to the defrost and drain pan heaters. This added heat load causesthe controller to open the suction modulating valve to match the increased heat load while still holding the supplyair temperature very close to the set point.Opening the modulating valve reduces the temperature of the evaporator coil surface, which increases the rate atwhich water is condensed from the passing air. Removing water from the air reduces the relative humidity. Whenthe relative humidity sensed is 2% below the set point, the controller de-energizes the heat relay. The controller willcontinue to cycle heating to maintain relative humidity below the selected set point. If the mode is terminated by acondition other than the humidity sensor, e.g., an out-of-range or compressor shutdown condition, the heat relay isde-energized immediately.Two timers are activated in the dehumidification mode to prevent rapid cycling and consequent contactor wear.They are:• Heater debounce timer (three minutes)• Out-of-range timer (five minutes)The heater debounce timer is started whenever the heater contactor status is changed. The heat contactorremains energized (or de-energized) for at least three minutes even if the set point criteria is satisfied.The out-of-range timer is started to maintain heater operation during a temporary out-of-range condition. If the sup-ply air temperature remains outside of the user selected in-range setting for more than five minutes, the heaters willbe de-energized to allow the system to recover. The out-of-range timer starts as soon as the temperature exceedsthe in-range tolerance value set by function code Cd30.4.3.11 Perishable, Dehumidification - Bulb ModeBulb mode is an extension of the dehumidification mode, which allows changes to the evaporator fan speed and/ordefrost termination set points.Bulb mode is active when function code Cd35 is set to “Bulb”. Once the bulb mode is activated, the user may thenchange the dehumidification mode evaporator fan operation from the default (speed alternates from low to higheach hour) to constant low or constant high speed. This is done by toggling function code Cd36 from its default of“alt” to “Lo” or “Hi” as desired. If low speed evaporator fan operation is selected, the user has the additional capa-bility of selecting dehumidification set points from 60 to 95% (instead of the normal 65 to 95%).In addition, if bulb mode is active, function code Cd37 may be set to override the previous defrost termination ther-mostat settings (refer to Section 5.10.4) The temperature at which the defrost termination thermostat will be con-sidered “open” may be changed [in 0.1C (0.2F) increments] to any value between 25.6C (78F) and 4C(39.2F). The temperature at which the defrost termination thermostat is considered closed for interval timer startor demand defrost is 10C (50F) for “open” values from 25.6C down to a 10C setting. For “open” values lowerthan 10C, the “closed” values will decrease to the same value as the “open” setting. |
Related manuals for Carrier 69NT40-541-306
This manual is suitable for:
manualsdatabase
Your AI-powered manual search engine