mode and the heaters will be energized . The unit will transition back to the perishable idle mode when the temperature rises to 0.2_C (0.4_F) below the set point and the heaters will de-energize
3.3.7 Perishable Mode -- Economy
The economy mode is an extension of the conventional mode. The mode is activated when the setting of function code Cd34 is “ON”. Economy mode is provided for power saving purposes. Economy mode could be utilized in the transportation of temperature tolerant cargo or non-respiration items which do not require high airflow for removing respiration heat. There is no active display indicator that economy mode has been activated. To check for economy mode, perform a manual display of code Cd34.
In order to achieve economy mode, a perishable set point must be selected prior to activation. When economy mode is active, the evaporator fans will be controlled as follows:
At the start of each cooling or heating cycle, the evaporator fans will be run in high speed for three minutes. They will then be switched to low speed any time the supply air temperature is within ¦ 0.25_C (0.45_F) of the set point and the return air temperature is less than or equal to the supply air temperature + 3_C (5.4_F). The fans will continue to run in low speed for one hour. At the end of the hour, the evaporator fans will switch back to high speed and the cycle will be repeated. If bulb mode is active, the economy fan activity will be overwritten.
3.3.8 Perishable Mode -- Dehumidification
The dehumidification mode is provided to reduce the humidity levels inside the container. The mode is activated when a humidity value is set at at function code Cd33. The display module SUPPLY led will flash ON and OFF every second to indicate that the dehumidification mode is active. Once the Mode is active and the following conditions are satisfied, the controller will activate the heat relay to begin dehumidification.
1.The humidity sensor reading is above the set point.
2.The unit is in the perishable steady state mode and supply air temperature is less than 0.25_C above set point.
3.The heater debounce timer (three minutes) has timed out.
4.Heater termination thermostat (HTT) is closed.
If the above conditions are true the evaporator fans will switch from high to low speed operation. The evaporator fan speed will switch every hour thereafter as long as all conditions are met (see Bulb Mode section for different evaporator fan speed options). If any condition except for item (1) becomes false OR if the relative humidity sensed is 2% below the dehumidification set point, the high speed evaporator fans will be energized.
In the dehumidification mode power is applied to the defrost and drain pan heaters. This added heat load
causes the controller to open the suction modulating valve to match the increased heat load while still holding the supply air temperature very close to the set point.
Opening the modulating valve reduces the temperature of the evaporator coil surface, which increases the rate at which water is condensed from the passing air. Removing water from the air reduces the relative humidity. When the relative humidity sensed is 2% below the set point , the controller de-energizes the heat relay. The controller will continue to cycle heating to maintain relative humidity below the selected set point. If the mode is terminated by a condition other than the humidity sensor, e.g., an out-of-range or compressor shutdown condition, the heat relay is de-energized immediately.
Two timers are activated in the dehumidification mode to prevent rapid cycling and consequent contactor wear. They are:
1.Heater debounce timer (three minutes).
2.Out-of-range timer (five minutes).
The heater debounce timer is started whenever the heater contactor status is changed. The heat contactor remains energized (or de-energized) for at least three minutes even if the set point criteria are satisfied.
The out-of-range timer is started to maintain heater operation during a temporary out-of-range condition. If the supply air temperature remains outside of the user selected in-range setting for more than five minutes, the heaters will be de-energized to allow the system to recover. The out-of-range timer starts as soon as the temperature exceeds the in-range tolerance value set by function code Cd30.
3.3.9 Perishable, Dehumidification -- Bulb Mode
Bulb mode is an extension of the dehumidification mode which allows changes to the evaporator fan speed and/or defrost termination set points.
Bulb mode is active when configuration code Cd35 is set to “Bulb”. Once the bulb mode is activated, the user may then change the dehumidification mode evaporator fan operation from the default (speed alternates from low to high each 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, this gives the user the additional capability 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 thermostat settings. (Refer to paragraph 4.9.5.) The temperature at which the defrost termination thermostat will be considered “open” may be changed [in 0.1_C (0.2_F) increments] to any value between 25.6_C (78_F) and 4_C (39.2_F) . The temperature at which the defrost termination thermostat is considered closed for interval timer start or demand defrost is 10_C for “open” values from 25.6_C (78_F) down to a 10_C setting. For “open” values lower than 10_C, the “closed” values will decrease to the same value as the “open” setting. Bulb mode is terminated when:
