9 CONTROL OPERATION
The Liebert MC Premium Efficiency Control takes approximately 30 seconds to boot up once power is
applied to the condenser. The LED on the Premium Efficiency Control Board reads “888” while the board
is booting up. Once the control has booted up, the display shows “F00” and then the value for F00. With
the control operational, the condenser fan(s) turn in less than 5 seconds after receiving a signal from the
indoor unit that the compressor(s) are On. Consider using UPS equipment on both data center cooling
units and Liebert MC condensers to maintain uninterrupted cooling capability.
For the first 60 seconds of operation after the compressor turns on, the condenser fan(s) will run at a fixed
speed, set at the factory, based on ambient temperature: faster at higher temperatures, slower at lower
temperatures. After 60 seconds, the control adjusts the fan speed based on the liquid pressure
transducer. If the liquid pressure transducer fails, the condenser uses temperature sensors to control the
fan speed based on the liquid line temperature. The condenser fans continue to operate for
approximately 30 seconds after compressors turn Off.
The Liebert MC fans have various alarm conditions, such as loss of voltage and loss of control signal, that
will stop the condenser fans. Once the alarm condition is no longer present the Liebert MC fans will turn
on automatically if compressors are On.
9.1 Premium Efficiency Control Board and Interface
The Liebert MC Premium Efficiency Control board has a stacked board arrangement. There are three
seven-segment LED’s and four keys as human machine interface (see Figure 9.2 on page91).
NOTE: Indicator lights should be On to indicate signal is present. See Figure 9.1 on the next page, #1, 2
and 3.
Vertiv | Liebert® MC™ Installer/User Guide | 89
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