Continuous Temperature Control Operation

The controller regulates compressor operation based the return air sensor and setpoint temperatures to determine operating mode switch points. The controller operates the unit on:

• Cool mode

• Null mode

• Defrost mode

• Evaporator fans operate on low speed to continuously circulate air inside the container (except during defrost).

• Controller LED display shows the return air sensor temperature.

• Controller LCD display shows the setpoint.

Cool

• After initial start-up and pull-down to 1.0 C (1.8 F) below setpoint, the controller calls for the Cool mode whenever the return air temperature increases more than 1.0 C (1.8 F) above setpoint.

• Unit operates in Cool mode for a minimum of 6 minutes to prevent rapid cycling between Cool and Null.

• After initial pull-down to setpoint, the controller keeps the In-range LED ON as long as the return air temperature remains less than 1.5 C (2.7 F) above setpoint.

Null

• The controller calls for Null when the Return Air Temperature decreases more than 1.0 C (1.8 F) below setpoint.

• The controller de-energizes the compressor contactors and condenser fan contactor, stopping the both compressors and the condenser fan.

• Units remains in Null mode for a minimum of 6 minutes to prevent rapid cycling between Cool and Null.

• The evaporator fans continue to operate in low speed.

During the Cool or Null modes, the controller initiates the Defrost mode when the evaporator coil sensor temperature is below 18 C (65 F) and:

• Demand defrost function determines that defrost is required when the temperature difference between the return air sensor and setpoint increases to a preset value and a minimum of 6 hours of compressor ON (running) time have elapsed since the previous defrost.

• A manual defrost is initiated by pressing the Defrost special function key or by Refcon Remote Monitoring Modem (RMM).

  Note If unit operating conditions do not allow the unit to enter a defrost cycle, “Defrost Not Activated” appears on VGA display when the DEFROST key is pressed.

• A Timed Defrost always starts at 1 minute past the hour immediately following a defrost timer request for defrost. For example, if the defrost timer requests a defrost cycle at 7:35, the defrost cycle will start at 8:01. The datalogger will record a Defrost event for each log interval in which a Defrost cycle is pending or active (i.e. both the 8:00 and 9:00 data logs on 1 hour logging interval).

• On Frozen Loads, the initial time interval is 12 hours. Six (6) hours are added to the time interval each time a timed defrost interval occurs without a demand defrost in between. Maximum accumulated time interval is 36 hours. Time interval resets to 12 hours when setpoint is changed more than 5 C (9 F); or if the unit is turned OFF for 12 hours.

When the defrost mode is initiated:

• The controller de-energizes both the R-134a and R-23 compressor contactors, the condenser fan contactor and the evaporator fan contactors; stopping the compressors, condenser fan and evaporator fans.

• When the compressors stop, the controller turns ON the heater output, turning on the electric heaters.

The controller terminates the defrost mode when:

• Frozen mode: Evaporator coil sensor temperature reaches 18 C (65 F).

• Time/temperature function: If the evaporator coil sensor exceeds 8 C (47 F) for 15 minutes, the controller terminates defrost.

• Interval timer: Controller terminates defrost 90 minutes after initiation if the coil sensor temperature has not terminated defrost (120 minutes if power supply is less than 55H). Alarm code 20 will be generated if this occurs.

• When the controller terminates Defrost, the heater contactor is de-energized. The controller starts the condenser fan and the R-134a compressor. After 30 seconds, the controller starts the R-23 compressor and the evaporator fans to minimize heat energy release into the container.