Carrier 23XL Spezifikationen PDF herunterladen (Seite 8)

• positions the slide valve for capacity control. The slide valve

is connected to a piston via a rod. The position of the pis-

ton, which rides in a cylinder, is determined by energizing

one of two solenoids which function to supply and equal-

ize oil pressure to and around the piston. This allows the

slide valve to unload and load.

• seals the gap between the male and female rotors. The oil

hydrodynamically seals this space to allow the refrigerant

vapor to be compressed. A speciﬁc ﬂow rate of oil is in-

jected into the compressor rotor housing at the point where

the compression process is initiated.

• cools the compressed refrigerant vapor. The oil that is in-

jected into the compressor for sealing also acts as a heat

sink by absorbing a portion of the heat from compression.

Thus, constant and cool compressor discharge gas tem-

perature, relative to an oil-less screw compressor, is

maintained.

Oil is charged into the system through a hand valve lo-

cated on the bottom of the oil sump (Frame 1 and 2 ma-

chines) or separator (Frame 4 machines). Sight glasses on

the oil sump (Frame 1 and 2 machines) and/or oil separator

(Frame 4 machines) permit oil level observation. When the

compressor is shut down, an oil level should be visible in

the oil sump (Frame 1 and 2 machines) or the lower oil

separator sight glass (Frame 4 machines). During operation,

the oil level should rise and be visible in the oil

separator sight glass (Frame 1 and 2 machines) or the upper

oil separator sight glass (Frame 4 machines). Approxi-

mately 4.2 gal. (15.9 L) of an oil and refrigerant mixture

accumulates in the sump of Frame 1 and 2 machines.

Approximately 10 gal (38 L) of oil accumulates in the sepa-

rator and 2 gal. (7.6 L) accumulates on the cooler of

Frame 4 machines.

Oil is driven from the oil separator through an oil ﬁlter to

remove foreign particles. The oil ﬁlter has a replaceable car-

tridge. The ﬁlter housing is capable of being valved off to

permit removal of the ﬁlter (see Maintenance sections, pages

63-68, for details). The oil then travels through a shutdown

solenoid and past a pressure transducer to three separate in-

lets on the compressor. The oil pressure measured by the trans-

ducer is used to determine the oil pressure differential and

pressure drop across the oil ﬁlter. The oil pressure differen-

tial is equal to the difference between the oil pressure trans-

ducer reading and the evaporator pressure transducer read-

ing. It is read directly from the Local Interface Device (LID)

default screen.

Part of the oil ﬂow to the compressor is directed to the

slide valve and is used for capacity control positioning. The

remaining oil ﬂow is divided between the rotors and bear-

ings. A speciﬁc quantity is sent to the rotors and injected at

the start of compression to seal the clearances between the

rotors. Another portion is sent to the bearings and used for

lubrication.

Oil leaves the compressor mixed with the compressed dis-

charge refrigerant vapor. The mixture then enters the oil sepa-

rator, where oil is removed from the refrigerant and collected

at the bottom to complete the cycle.

FRAME 1 AND 2 MACHINES — The oil and refrigerant

vapor mixture enters the oil separator through a nearly tan-

gential nozzle, giving a rotational ﬂow pattern. Oil is thrown

to the sides of the oil separator and runs down the walls to

a chamber in the bottom where it drains to the sump. A baffle

separates this chamber from the vortex ﬂow to prevent re-

entrainment. Gas ﬂows up through a vortex funnel to a re-

movable coalescing element where the rest of the oil collects.

This oil runs down the element surface to a scavenge line

which is piped to the ﬁrst closed lobe port.

FRAME 4 MACHINES — The oil and refrigerant vapor mix-

ture is directed against the rear wall of the oil separator as

it enters the side of the oil separator. This action causes the

bulk of the oil to drop from the refrigerant and collect at the

bottom of the oil separator. A mesh screen is provided near

the oil separator outlet to remove any additional oil which

may still be entrained in the refrigerant vapor.

The oil sump (Frame 1 and 2 machines) contains a level

switch, temperature sensor, 500-watt oil heater (Frame 1 and

2 machines), and oil ﬁlter. Oil temperature is measured and

displayed on the LID default screen. During shutdown, oil

temperature is maintained by the Product Integrated Control

(PIC). See Oil Sump Temperature Control section on

page 29.

NOTE: Frame 4 machines do not have an oil heater.

Operating oil pressure must be at least 20 psi (138 kPa)

for HCFC-22 [7 psi (48.3 kPa) for HFC-134a] and is

dependent upon system pressure differential (lift). The oil

pressure transducer is located downstream of the ﬁlter, so

the value displayed on the LID will be slightly less than the

lift value. Under normal full load conditions, oil pressure is

approximately 120 psi (827 kPa) [76 psi (517 kPa)]. If suf-

ﬁcient system differential pressure is not established or main-

tained, oil pressure will not be established (or will be lost)

and machine shutdown will result.

The compressor provides a pressure differential, but the

system pressure differential is constrained by the tempera-

tures of the chilled and tower water circuits. Cold tower wa-

ter, rapid tower water temperature swings, and high return

water temperature are among the factors which could con-

tribute to frequent low oil pressure alarms. To help ensure

that suitable oil pressure is established at start-up, sufficient

tower water control should exist. Increasing the machine ramp

loading rate will allow faster compressor load up. This will

quickly establish the refrigerant and, therefore, oil pressure

differential. Units equipped with poppet valves provide a mini-

mum pressure differential to ensure oil pressure at start-up.

See the Troubleshooting Guide section on page 68 for fur-

ther information.

Conversely, rapid loading of the compressor could cause

any refrigerant in the oil to ﬂash due to the sudden drop in

suction pressure. If the resulting oil foam is not pumped ef-

ﬁciently, oil pressure drops and poor lubrication results. There-

fore, the PIC control follows an internal oil pressure ramp

loading schedule during initial start-up.

If the start-up oil pressure falls below the values speciﬁed

in Table 1, the PIC control will shut down the machine.

Table 1 — Oil Pressure Ramp-Up Rate

TIME

(SEC)

MINIMUM START-UP OIL PRESSURE REQUIREMENT

HCFC-22 HFC-134a

psi kPa psi kPa

40 4 27.6 1.4 9.7

80 11 75.8 4 27.6

120 20 137.9 7 48.3

Oil Reclaim System — The oil reclaim system oper-

ates to return oil from the cooler back to the compressor.

FRAME 1 AND 2 MACHINES — The oil reclaim system

returns oil back to the compressor using discharge gas pres-

sure to power an ejector. The oil and refrigerant mixture is

vacuumed from the top of the cooler liquid refrigerant level

and discharged into the compressor suction port.

FRAME 4 MACHINES — Frame 4 machines do not re-

quire an oil reclaim system.

Oil Loss Prevention — The suction pan is located on

top of the cooler, where oil collects during low-load opera-

tion. The cooler is designed so that when oil drains into the

cooler from the compressor during low loads, it will be re-

entrained with the suction gas ﬂow.

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