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avoiding liquid slugging at the compressors and ensuring

operating stability.

5.15 - Motor cooling valve control

The temperature of the motor windings is controlled to a set-

point of 82°C. This is achieved by cycling of the motor cooling

valves to allow the liquid refrigerant to flow across the motor

windings, if necessary. On units equipped with economizers

with plate heat exchangers, a thermostatic valve controls the

necessary refrigerant flow entering this heat exchanger and

continuously flowing over 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.

5.16 - 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 8 fan stages, of which

one per circuit is a variable speed fan, depending on their

configuration and wiring.

5.17 - 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.

5.18 - 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 item 5 of the information menu.

• 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, description of the control contacts.

• With a network command when the unit is in CCN opera-

ting type (CCn).

5.19 - 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

protection 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 protec-

tion function. An alarm is activated, if the high pressure is

still too high.

5.20 - High current load shedding function

This function does not require an additional board. It prevents

high current breaks on each compressor by the following

means:

• Preventing any capacity increase on the compressor once

the high current value has reached an initial threshold

• Shedding one or more capacity stages once a second

protection 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.

5.21 - 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 prelubrica-

tion 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.

5.22 - Master/slave assembly

Two PRO-DIALOG Plus units can be linked to produce a master/

slave assembly. The two machines are interconnected over the

CCN bus. All parameters required for the master/slave function

must be configured through the Service configuration menu.

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Carrier 30HX PRO Especificaciones Pagina 30

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