Emerson Liebert DS Precision Cooling System 28-105kW User Manual

When the Liebert Air Economizer is not operating, the outside air damper is closed, the return air 

damper is open and the relief air vent fan is shut down. This permits air from the conditioned space to 

be drawn into the primary cooling unit, cooled and expelled into the conditioned space. The relief air 

vent is not required while the Liebert Air Economizer is not in service because no air volume is being 

brought into the conditioned space.

When a non-Liebert mixing box and damper motors are used, make sure that the following 

configurations are verified before a unit is placed into service.
• No power to Liebert unit means that there is no power applied to the Liebert Air Econo-

mizer damper motors. Without a spring return motor, the dampers will remain in the last 

position they were in when power was present. Spring return operation during a no-power 

condition should always be verified at startup.
• While the Liebert Air Economizer is not operating, which could be due to the outdoor air 

conditions, a manual lockout through the Liebert iCOM or a Unit Off state will result in 

2VDC being present on the associated indoor and outdoor analog outputs. The 2VDC signal 

must result in the outdoor damper being closed and return damper opened.
• During full Liebert Air Economizer operation, theLiebert iCOM will send 10VDC to the 

return and outdoor damper which must open the outdoor damper and close the return damper 

to its minimum position of 15%.

Risk of improper operation. Could cause frozen coils, resulting in degraded operation, water 

leaks, equipment damage and building damage.
Failure to verify that the indoor and outdoor damper operation is correct could result in the 

freezing of chilled water coils, condensation within the data center or a main fan overload.