Emerson Liebert DS Precision Cooling System 28-105kW Manuel D’Utilisation

When the fan control mode is placed into “Auto” and the supply air sensor is set to “Control,” the fan 

will modulate with the first stage of cooling.
Fan Ramps with Liebert Air Economizer when available and will be at 100% when the outdoor 

damper is at 100%. This will provide the most capacity from the Liebert Air Economizer and will help 

in holding off the mechanical cooling (2nd Stage). When the Liebert Air Economizer is not available, 

the fan will still ramp with the first stage of cooling but the first stage will be either a chilled water 

valve or compressor operation.
For other control modes, refer to the variable speed fan section of the Liebert iCOM manual. Those 

modes are not affected by the Liebert Air Economizer operation.

During startup, the Liebert Air Economizer airflow sensor will need to be calibrated. To calibrate 

follow the next steps.
1. Place a voltmeter on Terminals 24 and 50.
2. Locate the Liebert Air Economizer air flow sensor.
3. Turn the airflow sensor counterclockwise until the voltmeter indicates 0VAC.
4. Then turn the airflow sensor adjustment screw clockwise until the voltmeter indicates 24VAC.
5. When the voltmeter shows 24VAC, turn the screw counterclockwise one full turn.

Upon startup after a loss of power to the Liebert iCOM control board, the main fan will operate at 

100% for the first 5 minutes of operation. After running at 100% for 5 minutes, the standard fan 

control will be able to modulate the fan.?Does this apply in Manual Mode?

The Liebert Air Economizer can be disabled through a deactivation switch field-installed and wired to 

Terminals 24 and 51 in place of the factory-supplied jumper. Removing a factory-installed jumper will 

deactivate the unit’s function (see Figure 14). Deactivating the Liebert Air Economizer will transfer 

all cooling to the primary cooling unit.

The Liebert Air Economizer control uses an outdoor temperature humidity sensor to detect when 

outdoor conditions are within the operating range. The outdoor sensor can be monitored from the 

Service/Economizer data menu on page 2 of 3 (see Figure 12).

24

51

Liebert Air Economizer
Deactivation Switch
Terminals 24 and 51

Factory-Installed Jumper
Customer must remove jumper
and connect normally closed
contact to Terminals 24 and 51.
Open the contact to deactivate
the Liebert Air Economizer
functionality.
Main unit will continue to run without
the Liebert Air Economizer feature.

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