Carrier 23XL Dokumentacja Pobierz pdf (Strona 11)

In addition, the PIC Controls minimize oil loss to the cooler

once the rotor inlet temperature sensor detects hot oil drain-

ing down the suction pipe.

If the rotor inlet temperature increases 4 F (2.2 C) on Frame

1 and 2 machines or 8 F (4.4 C) on Frame 4 machines above

the leaving chilled water temperature, the slide valve is pro-

portionately moved in the load direction to increase suction

gas velocity. If the leaving chilled water temperature is then

brought 5 F (2.8 C) below the control point temperature, the

PIC will bring the machine into the recycle mode.

Slide Valve Principle — Oil ﬂow to the slide piston is

controlled by two solenoid valves. Each solenoid is operated

by load and unload signals from the PIC control.

To unload the compressor, the unload solenoid valve is

energized and the load solenoid valve is deenergized. This

conducts high pressure oil to the cylinder, retracting the op-

erator shaft, and modulating the slide valve toward the open

position. See Fig. 6. The slide valve opening vents com-

pressed gas back to the suction port on the compressor, re-

tarding the start of the compression process.

To load the compressor, the unload solenoid valve is deen-

ergized and the load solenoid valve is energized. This bleeds

oil from the cylinder to the suction pressure area within the

compressor housing. Forces resulting from the discharge-to-

suction pressure differential are then allowed to push the slide

valve toward the closed (fully loaded) position. See Fig. 7.

When the slide valve is closed, the compressor pumps the

maximum gas ﬂow.

Extension and retraction of the operator shaft position

the slide valve along the bottom of the rotors. The valve po-

sition controls the gas ﬂow rate delivered by the

compressor.

STARTING EQUIPMENT

The 23XL requires a motor starter to operate the hermetic

compressor motor and various auxiliary equipment. The starter

serves as the main ﬁeld wiring interface for the contractor.

Two types of unit mounted starters are available from Car-

rier Corporation: solid-state and wye-delta. See Carrier Speci-

ﬁcation Z-375 for speciﬁc starter requirements. All starters

must meet these speciﬁcations in order to properly start and

satisfy mechanical safety requirements. Starters may also be

supplied as separate, free-standing units.

Inside the power panel are 3 separate circuit breakers. Cir-

cuit breaker CB1 is the compressor motor circuit breaker.

The disconnect switch on the starter front cover is connected

to this breaker.

The main circuit breaker (CB1) on the front of the starter

disconnects the main motor current only. Power is still

energized for the other circuits. Another circuit breaker

inside the starter must be turned off to disconnect power

to PIC controls and oil heater (Frame 1 and 2

machines).

Circuit breaker CB2 supplies power to the control and oil

heater power (Frame 1 and 2 machines) supply circuit breaker

and portions of the starter controls.

All starters are shipped with a Carrier control module called

the Starter Management Module (SMM). This module con-

trols and monitors all aspects of the starter. See the Controls

section on page 13 for additional SMM information. All starter

replacement parts are supplied by the starter

manufacturer.

Unit Mounted Solid-State Starter (Optional) —

The 23XL may be equipped with a solid-state, reduced-

voltage starter (Fig. 5, 8A, 8B, and 9). This starter provides

on-off control of the compressor motor as its primary func-

tion. Using this type of starter reduces the peak starting torque,

reduces the motor inrush current, and decreases mechanical

shock. This is summed up by the phrase ‘‘soft starting.’’

Two varieties of solid-state starters are available as 23XL

options (Carrier supplied and installed). When a solid-state

starter is purchased with the 23XL, either a Benshaw, Inc. or

a Cutler-Hammert solid-state starter will be shipped with

the unit. See Fig. 8A and 8B. The manufacturer’s name will

be located inside the starter access door. See Fig. 9.

Fig. 5 — Screw Compressor Principle

Fig. 6 — Slide Valve Position at Unload

Fig. 7 — Slide Valve Position at Full Load

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