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Operation
13
Autorestart
When there is a loss of power to the cooling unit and power comes back, the unit will return to its pre-
vious operating status—on if it was on before the power off, off if it was off.
When power returns, the autorestart time—time-selectable: Single Unit Auto Restart (Service Menu,
Options Setup)—controls the start of the unit. The autorestart time runs in a loop, starting the next
unit each time when elapsed, starting with Unit # 1.
Loss of Power Alarm
A Loss of Power Alarm is activated when power is restored after an interruption. If acknowledged, the
alarm resets automatically after 30 minutes. This alarm can be set to different event types (Message,
Alarm or Warning) and can be disabled under menu item Loss of Power (Service Menu, Set Alarms).
Fan Alarm / Fan Protection Settings
The fan operation is protected by two digital devices: motor protection (optional) and a differential
pressure switch. The motor protection monitors for main fan overload and the differential pressure
switch ensures that the blower(s) are moving air. If either protection device triggers, an alarm will be
announced by a buzzer, alarm relay and event to monitoring after an adjustable time-delay (Main
Fan Overload and Loss Of Airflow in Service Menu, Set Alarms).
The time delay at the unit start is always five seconds shorter than the control delay (to avoid short
component starting when the fan is not working). During operation, the fan delay is fixed to
15 seconds.
There are two selection possibilities for both, Loss Of Airflow and Main Fan Overload:
• Shutdown—stops the unit (intended for DX models).
• Disable—stops the humidifier, electrical heaters and dehumidification; allows cooling and
free-cooling only (intended for chilled water models / external cooling).
3.1.2 Chilled Water Units with Variable Speed Motor
VSD Fan Speed (Auto or Manual VSD Fan Speed Control)
The parameter VSD Fan Speed (Service Menu, Setpoints) allows the cooling unit's fan motor speed to
be set for:
• Auto operation: when set to Auto, the speed of the VSD (variable speed drive) motor follows the
position of the chilled water valve based on predetermined logic for cooling and dehumidification
operation.
• Manual operation: when set to Manual, the speed of the VSD motor follows user input as set
either locally at the cooling unit's Liebert iCOM display (under VSD Setpoint in Service Menu,
Setpoints) or remotely using Modbus BMS signal with an optional Liebert IntelliSlot
®
485 card.
VSD Setpoint (VSD Fan Speed Setting)
If the VSD Fan Speed Control (Service Menu, Setpoints) is set for Manual, the VSD Fan Speed Set-
point (Service Menu, Setpoints) may be set for the desired speed of the variable speed motor.
Depending on the product control design, there may be an internal minimum speed, as defined by
that specific product operation, while the customer input may be set for 0-100%:
• Fan speed may be set locally at the unit using the Liebert iCOM display.
• Fan speed may be set remotely via a BMS signal (sent via Modbus using an optional Liebert Intel-
liSlot 485 card), which then transmits to the unit local control.
NOTE
Loss of power alarm will be activated only on units that had the fan on before power was lost.
NOTE
When the Main Fan Overload alarm is active, the Loss of Airflow alarm is masked out.