Continuous Temperature Control Operation

The controller regulates the compressor, digital control valve, and electric heaters based on a Control Temperature Differential (Refer to Compressor Digital Control Valve for more detail). This means the unit operating mode can not be predicted based only on the setpoint and supply air temperature. At setpoints of -9.9 C (14.1 F) and above, the controller operates the unit on the following:

• Cool mode with Modulation.

• Controller energizes the vapor injection valve continuously when the cool capacity is 100 percent.

• Heat mode (electric heaters pulse on and off on a 60 second duty cycle).

• Defrost mode (electric heaters on, evaporator fans off).

Chill Load Control Sequence (Setpoints at -9.9 C [14.1 F] and Above) Open
		A	Cool with Modulation (control temperature differential is above setpoint)
		B	Heat (electric heaters pulse on and off on a 60 second duty cycle if the control temperature differential is below setpoint.)
		C	In-range (based on supply air temperature)
		1	Decreasing Temperature
		2	Setpoint
		3	Increasing Temperature

1Setpoint temperature and controlling mode setting determine the evaporator fan speed:

• Normal Operation: Chill Loads - High or low speed fans; Frozen Loads - Low speed fans or no fans.

2Vapor injection valve:

• Chill, Frozen, or Power Limit Mode: When the cool capacity is 100 percent.

• Compressor High Temperature Protection: When the compressor discharge temperature exceeds 138 C (280 F).

3Condenser fan pulses on and off on a 30 second duty cycle to maintain a minimum condenser temperature:

• Chill Loads: Controller maintains a minimum 30 C (86 F) condenser temperature.

• Frozen Loads: Controller maintains a minimum 20 C (68 F) condenser temperature.

4Digital Control valve modulates:

• Chill Loads - whenever the unit is in a Cooling mode; Power Limit - whenever the unit is in Power Limit mode.

• Dehumidification: When the Dehumidify mode is set to On, the supply air temperature must be In-range to energize the electric heaters.

  • When the humidity is two percent or more above humidity setpoint, the controller (energizes) the heaters.

5Controller energizes electric heaters for heat, defrost and dehumidification:

• Heat mode (compressor off): If supply air temperature is too low, heaters pulse on and off on a 60 second duty cycle.

• Defrost mode: Heaters are on until evaporator coil temperature increases to terminate defrost.

• Controller calls for the Cool mode whenever the Control Temperature Differential (based on supply air temperature) is above setpoint.

• Controller turns on the Compressor indicates when the compressor is operating.

• Controller opens and closes Digital Control valve to control the compressor load. The duty cycle of the Digital Control valve balances the unit cooling capacity against the actual load requirements.

• Controller turns the In-range LED solid when the supply air sensor temperature is within 1.5 C (2.7 F) of setpoint.

• Controller turns on the Heat indicator whenever the heaters are pulsed on and off.

• If the supply air temperature is too low and the Control Temperature Differential is below the setpoint, the controller stops the compressor. The fans (low speed) are kept on to determine if fan heat is sufficient to increase temperature to setpoint. If not, switch to high speed. If not sufficient heat - increase with pulsating on the heaters until setpoint is reached.

At setpoints of -10 C (14 F) and below, the controller locks out the Modulation and Heat modes. The controller regulates compressor operation based the return air sensor and setpoint temperatures. The controller operates the unit on:

• Cool mode.

• Null mode.

• Defrost mode (electric heaters on, evaporator fans off).

• Evaporator fans operate on low speed and continuously circulate air inside the container (except during Defrost and in Null mode).

• Controller display shows the return air sensor temperature.

• Controller display shows the setpoint temperature.

• Controller cycles a single-speed condenser fan on for 2 to 30 seconds every 30 seconds when the unit is on air-cooled condenser operation. The amount of on time depends on the condenser coil, ambient and compressor discharge temperatures.

• Power limit is active during initial start-up and pull-down when the unit is cooling at return air temperatures above -10 C (14 F).

Open
		A	Cool
		B	In-range
		C	Null
		1	Decreasing Temperature
		2	Setpoint
		3	Increasing Temperature

• After initial start-up and pull-down to 2.0 C (3.6 F) below setpoint, the controller calls for the Cool mode whenever:

  • Return air temperature increases more than 0.2 C (0.36 F) above setpoint.

  • Return air temperature is above setpoint and the compressor has been off for 30 minutes.

• Controller turns on the Compressor indicator when the compressor is operating.

• Compressor must operate for a minimum of 5 minutes after startup.

• After initial pull-down to setpoint, 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.

• The controller calls for Null when the return air temperature decreases more than 2.0 C (3.6 F) below setpoint.

• The controller stops the compressor and condenser fan and evaporator fan.

The evaporator coil sensor temperature must be below 18 C (65 F) to initiate a Demand Defrost or Manual Defrost. The evaporator coil sensor temperature must be below 4 C (39 F) to initiate a Timed Defrost.

• Demand Defrost function initiates Defrost immediately when:

  • Temperature difference between the return air sensor and defrost (evaporator coil) sensor is too large.

  • Temperature difference between the supply sensors and return air sensor is too large.

• Manual Defrost may be initiated immediately by pressing the DEFROST key or by REFCON Remote Monitoring Modem (RMM).

• 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 Chill Loads (setpoints at -9.9 C [14.1 F] and above), the conditions for this are:

  • Evaporator Coil Temperature must be below 4 C (41 F) to activate the defrost compressor hour timer.

  • There is an interval set for defrosting, however, the defrost timer is built intelligent - it detects whether or not there is ice building up on the coil.

  • If there is no ice building up on the coil, it extends the defrost interval, and if there is Ice building up earlier on the coil it reduces the defrost interval. The maximum interval is 48 hours.

• On Frozen Loads, the initial time interval is 8 hours. Two (2) hours are added to the time interval each timed defrost interval. Maximum accumulated time interval is 24 hours.

• Defrost timer resets if the unit is off more than 12 hours, setpoint is changed more than 5 C (8.9 F) or PTI (pretrip) test occurs.

When the Defrost mode is initiated:

• The controller stops the compressor, condenser fan and evaporator fans.

• When the compressor stops, the controller turns on the Defrost indicator, Heat indicator and energizes the solid state, turning on the electric heaters.

The controller terminates the Defrost mode when:

• Evaporator temperature:

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

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

• Interval timer: Controller terminates defrost after 90 minutes on 60 Hz power (120 on 50 Hz power). Alarm Code 20 will be generated if this occurs.

• Power off: Turning UNIT ON/OFF switch OFF terminates defrost.

When the defrost mode is terminated:

• The Heat and Defrost indicators turn off and the solid state is de-energized. The controller starts the compressor to pre-cool the evaporator coil. The condenser fan starts if required.

The controller pre-cools the evaporator coil to the supply air temperature (or for 3 minutes maximum) to minimize heat energy release into the container. The controller then starts the evaporator fans.