Emerson Liebert iCOM Manual De Usuario

Compressor Sequencing parameter (Service Menu, Options Setup) is intended to maintain equal run 

times between compressors. This setting has three selection possibilities:

• Always use Compressor 1 as lead compressor.
• Always use Compressor 2 as lead compressor.
• Auto:

• First priority: if the safety timings are acceptable for only one compressor, then it is the next 

to be started/stopped.

• If both compressors are Off: the one with fewer working hours is the next to start.
• If both compressors are in operation: the one that has been operating longer since the last 

start is the next to be stopped.

On water/glycol-cooled units with digital scroll compressors), pressure changes during each digital 

cycle during unloaded operation. This rapid pressure change would cause a conventional water 

regulating valve to open and close an excessive number of times.
Excessive valve cycling is avoided on units with digital scroll compressors) by monitoring a liquid line 

transducer and regulating heat exchanger fluid flow with a motorized ball valve (MBV). The control 

algorithm for the motorized ball valve uses an intelligent sampling rate and adjustable pressure 

threshold (S427 Ball Valve Setpoint Offset in Figure 169) to reduce the number of times the valve 

opens and closes. System reliability and performance is enhanced using a brass valve, linkage and 

actuator.
Each compressor has one motorized ball valve that is driven by the analog output of the Liebert iCOM 

based on discharge pressure. If there is a call for cooling, the compressor start is delayed by a 

30-second timer. During this delay, the motorized ball valve is set to 50% open to allow fluid flow 

through the unit condenser. The compressor will start after the 30-second timer elapses.
Motorized Ball Valve Manual Mode: (Service/Service, Figure 130) Manual operation can be 

selected to allow service personnel to control the motorized ball valve from the Liebert iCOM.
 When Auto BV Control is selected, the motorized ball valve functions as it would be during normal 

system operation.

When Manual BV Control is selected, the user must be careful in setting the MBV position because 

the ball valves will remain in the position set in the Service menu until the control is switched back to 

Auto or until a technician changes the valves to another manual position (the motorized ball valve in 

manual mode can be set in 1% increments from fully closed to fully open). Low or high discharge 

pressure may occur during this mode, depending on environmental conditions and the position of the 

motorized ball valve.
The motorized ball valve is driven by a 2-10VDC proportional control signal: the valve is closed at 

2VDC, 50% open at 6VDC and fully open at 10 VDC.

Once a compressor has stopped, the MBV control will continue to change the MBV position to 

maintain system pressures for a maximum time of 10 minutes by following the Auto BV control 

algorithm. When the 10-minute delay has expired or the discharge pressure is below its minimum 

threshold, the motorized ball valve will close until the next compressor activation.