Technical Specifications

Heat Rejection
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6.14.3 Extra-Low Voltage Control Wiring
Control interlock between the control enclosure and the indoor unit(s) or other source(s) is required.
Multiple indoor units may be connected in parallel if the controlled pumps will feed them all.
• Extra-low voltage, non-safety control wiring must be a minimum of 16 GA. (1.665 mm
2
) for up to
75 feet (22.9m), or not to exceed 1V drop in the control line.
• Install extra-low voltage control wiring (24V) from Terminals 70 & 71 on the wire raceway in the
compressor compartment of the indoor unit to Terminals 70 & 71 of the control enclosure.
• Extra-low voltage control wiring should also be installed between Terminals 24 and 50 from the
control enclosure to the indoor cooling unit’s common alarm or other alarm location for loss-of-
flow indication.
• Install extra-low voltage control wiring between the auxiliary terminals on the control panel to
Terminals 70 and 71 on the drycooler.
• The flow switch wiring should be connected to Terminals 77 and 74.
• Provide line voltage to power block(s) in control enclosure as shown in the electrical schematic.
• Install optional field-supplied disconnect if desired.
• Run three-phase line voltage from the control box to each individual pump motor.
6.14.4 Dual Pump Package Flow Switch
Mount the flow switch in a section of coolant supply/return piping where there is a straight run of at
least five (5) pipe diameters on each side of the flow switch.
• The switch should be mounted so the terminals or wire leads are easily accessible for wiring.
• Mount the flow switch in a standard 1" x 1" x 1" tee for one-inch pipe installation. Use a reducing
tee for larger sizes of pipe to keep the flow switch near the pipe and to provide adequate paddle
length in the flow stream.
• Screw the flow switch in position so the flat part of the paddle is at a right angle to the flow. The
arrow on the side of the case must point in the direction of the flow.
• The flow switch must be mounted in a horizontal pipeline.
6.14.5 Dual Pump Controls Sequence of Operation
On a call for cooling, the compressor contactor and/or the Econ-O-Coil relay in the Liebert unit is
energized. The relay and contactor are in the Liebert indoor evaporator section. Each compressor
contactor has a side switch wired in parallel with the Econ-O-Coil relay and is responsible for closure
of the low-voltage pump-control circuit.
This low-voltage circuit has a series of contactors, relays, selector switch and a flow switch. This
circuit controls the start of the pumps and provides contact closure to interlock the drycooler(s)
control circuit. Once the circuit is closed, 24V is passed to the pumps control circuit and the auxiliary
relays are energized, closing the drycooler(s) control circuit.
Pump P1 is factory-set to be the primary pump (Selector Switch 1-2). Voltage then passes through the
normally closed contacts of the R2 relay (standby pump relay), through the current overloads and to
the #1 pump contactor. At this point, the #1 pump and appropriate drycoolers are running.
When the pump establishes flow, it opens the system flow switch. The pump has approximately
10 seconds to establish full flow. If it does, the system will run in this state until the call for cooling is
satisfied and the circuit drops out. If this pump cannot establish flow or if it has been running and
fails, the flow switch will close and energize an adjustable relay, typically set for 10 seconds.
Once this relay times out, it energizes the R2 switch over relay. This relay will drop out the voltage to
the #1 pump contactor and energize the #2 pump contactor. Along with the R2 relay the AL relay
(alarm relay) will energize. This will provide a set of closed contacts for remote indication of the
switch-over situation.
Once the problem with the lead pump is repaired, the controls must be reset. To reset the control box,
turn Off the main power to the control box and then restore the main power to the control box. Pump
P1 then becomes the primary pump again.