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5.12 - Motor cooling valve control
The temperature of the motor windings is controlled to a
setpoint of 85°C. This is achieved by cycling of the motor
cooling valves to allow the refrigerant to flow across the motor
windings, if necessary. For units with economizer, instanta-
neous vapour leaves the high side of the economizer and
continuously flows across the motor windings. All refrigerant
used for motor cooling returns to the rotors through an orifice
situated mid-way along the compression cycle and is
compressed to the discharge pressure.
5.13 - Head pressure control on air-cooled units
• The saturated condensing temperature is controlled by
reference to a fixed setpoint (user-definable in the Setpoints
menu). This temperature is maintained by cycling fans on
and off, as well as by varying the speed of a fan.
NOTE: Certain units can have up to 4 fan stages and a vari-
able speed fan per circuit, depending on their configuration
and wiring.
5.14 - Head pressure control on water-cooled units
• The saturated condensing temperature is controlled by
reference to a user-definable fixed setpoint. This temperature
is maintained by using the valve to control the flow of water
in each condenser circuit.
5.15 - Head pressure setpoint selection
There are two head pressure setpoints available: the first is
called “head pressure setpoint” and the second “reclaim
setpoint”. These setpoints only have an effect when the control
system is controlling head pressure: air or water-cooled units
operating in cooling mode (only when they are fitted with
condenser water valves).
The active setpoint can be selected in one of the following
ways:
• With the operating type selector button: selections L-C1 and
L-C2 activate the head pressure setpoint. Selections LC1r
and LC2r activate the reclaim setpoint (see section 4.2.2,
description of the operating modes).
• With a volt-free selection contact connected to the customer
terminal block when the unit is in Remote operating type
(rEM). See section 3.4.4, description of the control contacts.
• With a network command when the unit is in CCN operating
type (CCn).
5.16 - High pressure load shedding function
This function does not require an additional board. It prevents
high pressure breaks on a circuit by the following means:
• Preventing any capacity increase on the circuit once the high
pressure value has reached an initial threshold.
• Shedding one or more capacity stages once a second protect-
ion threshold has been reached.
In the event of capacity stages being shed, no capacity increase
will be authorised on the circuit concerned for a period of 5
minutes.
NOTE: The last capacity stage cannot be shed by this protect-
ion function. An alarm is activated, if the high pressure is still
too high.
5.17 - Start-up procedure - prelubrication
This procedure describes the necessary procedures to ensure the
lubrication of the compressor before start-up.
The control follows the sequence below:
For the lead compressor (the first compressor in the circuit to
start):
1. Start the oil pump and measure the initial oil pressure.
2. Wait approximately 30 seconds.
3. Verify the oil solenoid valve tightness, i.e.: if oil pressure
increases and the solenoid valve is not open, the oil
solenoid valve failure alarm is activated and prelubri-
cation is stopped. The procedure is aborted.
4. If not, the oil solenoid valve is activated.
5. Wait approximately 15 seconds.
6. If oil pressure increases, prelubrication is assured and the
compressor can start.
7. If not, a further prelubrication cycle is started. Return to
point 1.
NOTE: After three cycles, the low oil pressure alarm at pre
start-up is acctivated, and prelubrication is also stopped.
For the lag compressor (one compressor in the circuit is already
in operation).
1. Activate the oil solenoid valve.
2. Wait approximately 15 seconds.
3. If oil pressure increases, prelubrication is assured and the
compressor can now start.
4. If not, the low oil pressure at start-up alarm is activated
and the prelubrication is also stopped.
5.18 - Master/slave assembly
5.18.1 - General
Two PRO-DIALOG Plus units can be linked to produce a
master/slave assembly. This feature is only authorised in
cooling mode. The two machines are interconnected over the
CCN bus. To operate as master/slave, both units must have
their chilled water temperature probes located on the common
evaporator entering and leaving line. In addition interlock
control of the cooler water flow and a freeze protection switch
is imperative on each unit.
The master/slave link only operates when both units are in
CCN operating mode. The master/slave assembly will be
inactive in the following cases:
• If either of the chillers is in Local or Remote mode, or in
heating mode.
• A demand limit command is sent to the slave unit.
• One of the following CCN variables is forced on the slave
unit: start unit, demand limit or control point.
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