
The Premium Efficiency Control board on a Liebert MC with a dual refrigeration circuit adjusts the speed
of fans on each circuit to match each circuit’s head pressure conditions. On a Liebert MC with multiple
fans and a single refrigeration circuit, the premium control adjusts the fans to the same speed to maintain
head pressure. The control system provides refrigerant head pressure control for outdoor ambient
temperatures as low as -30°F (-35°C), provided that the total design range (from minimum to maximum) is
125°F (70°C) or less. For traditional DX applications, Liebert Lee-Temp™kits are required only when the
design temperature ranges exceed 125°F (70°C) for standard match-ups and 115°F (65°C) for Liebert
Quiet-Line™match-ups.
Anti-Freezing Operation
The EC fans must be operated periodically in cold weather to reduce the possibility of lockup due to ice
and snow accumulation. During periods of inactivity and outdoor temperatures below 35°F (1.6°C), the EC
fans will spin for at least 30 seconds every 15 minutes at 60% of the maximum fan speed.
Fan Reversal for Cleaning
The Liebert iCOM®can be used to run the Premium EC fans in reverse to clear loose debris from the coil
between scheduled coil cleanings. The fan reversal may be done manually or automatically based on a
user-programmed schedule. Automatic fan reversal interval occurs when the indoor unit is Off (BMS Off,
U2U network standby or Remote Shut Down [RSD]).
Low-Noise Feature
The low-noise feature allows setting the condenser fans to operate at a specified speed to reduce
operating noise at certain times. Special match-ups of premium condensers are available for applications
needing to meet stringent sound regulations. Lower sound levels are achieved by oversizing the
condenser, which decreases the maximum airflow and sound level produced by the condenser. This
feature requires special setup of the indoor unit. One or more Liebert Lee-Temp receivers are required.
The premium control has gain schedules that will override the user-defined low-noise schedule to prevent
a high-pressure condition from occurring.
1.3 Liebert Lee-Temp™Refrigerant Control
The Liebert Lee-Temp head pressure control system utilizes head pressure control valve(s), extra
refrigerant and insulated refrigerant receiver(s) with heater pads to assist system starting. The Liebert
Lee-Temp control system also maintains proper operating head pressures in outdoor temperatures below
the rating point of the Liebert MC control type. The system works by flooding the condenser coil with
liquid refrigerant to a level that balances the system condensing requirements with the condenser coil
surface available to reject the system heat. During the summer, the system requires the entire condenser
coil surface for heat rejection and most of the refrigerant is stored in the receiver. In the winter, the same
amount of heat can be rejected by only a fraction of the coil surface. As head pressure begins to fall, the
control valve restricts the flow of liquid refrigerant from the condenser. This extra liquid refrigerant
reduces the effective condenser surface area available for heat transfer. The head pressure control valve
also bypasses hot gas into the receiver to warm the liquid and maintain liquid pressure for proper
operation of the expansion valve. Liebert Lee-Temp kit is optional for condensers and is field-installed.
Condenser control boards are factory-configured for Liebert Lee-Temp if they are ordered with Liebert
Lee-Temp receivers. They can be field-configured if a Liebert Lee-Temp system is added later.
Vertiv | Liebert® MC™ Installer/User Guide | 12