Carrier PrimeLINE 69NT40-561-200, Operation And Service Manual

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4–19 T-362
4.3 Modes of Operation
General operation sequences for cooling, heating and defrost are described in the following paragraphs.
Operational software responds to various inputs. These inputs come from the temperature sensors and pressure
transducers, the temperature setpoint, the settings of the configuration variables and the function code
assignments. The action taken by the operational software changes as the input values change. Overall interaction
of the inputs is described as a “mode” of operation. The modes of operation include perishable (chill) mode and
frozen mode. Descriptions of the controller interaction and modes of operation are provided in the following sub
paragraphs.
4.3.1 Start Up - Compressor Phase Sequence
At start up, the controller logic checks for proper phase sequencing and compressor rotation. If incorrect
sequencing is causing the compressor and three-phase evaporator fan motors to rotate in the wrong direction, the
controller will energize or de-energize relay TCP as required. Relay TCP will switch its contacts, energizing or de-
energizing relays PA and PB. Relay PA is wired to energize the circuits on L1, L2 and L3. Relay PB is wired to
energize the circuits on L3, L2, and L1, thus providing reverse rotation.
4.3.2 Start Up - Compressor Bump Start
At start up, the controller logic will initiate a compressor bump start procedure to clear liquid refrigerant from the
compressor. If suction and discharge pressures have equalized, the compressor will perform three compressor
bump starts. A compressor bump start may also occur after a defrost cycle has been completed.
During bump start, the EEV will close. Relays TS, TQ, TN, TE, and TV will be de-energized (opened). The result of
this action will close the ESV and shut all fans off. The compressor will start for 1 second, then pause for five
seconds. This sequence will be repeated two more times. After the final bump start, the unit will pre-position the
EEV to the correct starting position, pause and then start up.
4.3.3 Perishable Mode Temperature Control
In Perishable mode, the controller maintains the supply air temperature at setpoint, the SUPPLY indicator light is
illuminated and the default reading on the display window is the supply temperature sensor reading.
When the supply air temperature enters the in-range temperature tolerance (Cd30), the green IN-RANGE light will
energize. When CnF26 (Heat Lockout Temperature) is set to -10°C, Perishable mode is active with setpoints above
-10°C (+14°F). When CnF26 is set to -5°C, Perishable mode is active with setpoints above -5°C (+23°F).
4.3.4 Perishable Pulldown
When the system is in Perishable Pulldown mode, the highest priority is given to bringing the container down to
setpoint. When cooling from a temperature that is more than 2.5°C (4.5°F) above setpoint, the system will be in
Perishable Pulldown mode in economized operation. However, pressure and current limit functions may restrict the
valve if either exceeds the preset value.
4.3.5 Perishable Steady State
In Perishable Steady State mode, the control temperature is maintained near a setpoint that is above the heat
lockout temperature. Once setpoint is reached, the unit will transition to Perishable Steady State mode. This results
in unloaded operation by cycling the DUV to limit capacity and maintain steady temperature control.
The unit is capable of maintaining supply air temperature to /- 0.2°C (+/- 0.36°F) of setpoint. Supply air
temperature is controlled by positioning of the electronic expansion valve (EEV), cycling of the digital unloader
valve (DUV), cycling of the compressor, and cycling of the heaters.
4.3.6 Perishable Idle, Air Circulation
When it is unnecessary to run the compressor to maintain control temperature, the system enters Perishable Idle
mode. If the controller has determined that cooling is not required or the controller logic determines suction
pressure is at the low pressure limit, the unit will transition to Perishable Idle mode. During Perishable Idle mode,
the compressor is turned off, but the evaporator fans continue to run to circulate air throughout the container. If
temperature rises +0.2°C (0.4°F) above setpoint, the unit will transition back to Perishable Steady State mode.