User manual

Operation
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3.1.4 Compressor Sequencing on Two-Compressor Units
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.
3.1.5 Motorized Ball Valve in Water-Cooled Units
On water/glycol-cooled units, discharge pressure is controlled by a motorized ball valve (MBV).
During unloaded operation, pressure changes during each digital cycle could cause a pressure-
controlled water regulating valve to open and close an excessive number of times. The motorized ball
valve is designed to maintain a consistent peak discharge pressure.
The control algorithm for the motorized ball valve uses an intelligent sampling rate and adjustable
pressure thresholds to reduce the number of times the valve opens and closes. The valve assembly
consists of the 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) 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.
3.1.6 MBV Operation After Compressor is Turned Off
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.
NOTE
The Auto setting attempts to maintain equal run times between compressors.
NOTE
Compressor operation will be delayed 30 seconds to allow the motorized ball valve to position
itself for initial startup.