Dunham-Bush ACXi 165-5SP-LN, Installation, Operation And Maintenance Manual

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3.0 OPERATION
8. Turn control circuit power switch on, and all
individual compressor circuit switches. Press
computer keyboard reset key (RST).
Compressors should start after start-up clock
times out and will come on in sequence to
satisfy the existing load.
3.9 SAFETY RELIEF VALVES
Each pressure vessel is protected by a safety
relief valve as required by ASME Code. Each
compressor is protected by a relief valve which is
vented to atmosphere. Never install any kind of
shut-off valve in a safety relief vent line.
3.10
REFRIGERATION CYCLE
-MULTIPLE
COMPRESSOR
ACXi
Following is the normal sequence of operation
for a unit installed in a typical air conditioning
system. Refer to Figure 3.2, the typical piping
schematic for multiple compressor ACXi unit.
Each vertical screw compressor discharges hot,
high pressure gas into a hot gas manifold and is
then split and routed into the left-hand and right-
hand side, condenser where it condenses,
rejecting heat to the outdoor air drawn through
the coil by fans. The liquid refrigerant from the
condenser is drain out from bottom of the
condenser coil through liquid stop valve into a
liquid subcooler.
The refrigerant flows through the liquid
subcooler, dropping its temperature causing it to
flash. Liquid is cooled from the liquid subcooler,
drains to liquid line filters drier and sight glass,
liquid solenoid before through DX evaporator
main expansion valve which is at an intermediate
pressure between condenser and evaporator.
Refrigerant flows into the DX evaporator, where
it boils, cooling the water flowing outside
evaporator tubes. Vapor from the boiling
refrigerant flows up the suction pipes through
shut-off valves, suction check valves and suction
filters (inside compressor) into compressors
where it is compressed and starts the cycle again.
Vapor flows from the top of the liquid subcooler
into the compressors at the vapor injection ports,
which feed it into the compressors part way
through the compression process. Check valve
will prevent backflow at shutdown.
3.11 FAN CYCLING
On start-up, all fan will remain off (some units
may have base fans which run together with
compressor). As the head pressure builds up,
next fan stage will start. Subsequently fan stage
will start if the head pressure continues to rise.
Refer wiring circuit diagram for number of fan
stage.
3.12 LIQUID INJECTION
Each compressor is fitted with a liquid
injection system designed to feed refrigerant
liquid into the compressor to provide
additional motor cooling as required. The
liquid injection control TXV will modulate to
hold the compressor discharge gas temperature
below 170ºF, the maximum discharge
operating temperature of these compressors.
3.13 HYDRAULIC CAPACITY
CONTROL SYSTEM
Each compressor has a hydraulic control system
to supply the proper force necessary to actuate
the capacity control slide valve, thereby
regulating compressor loading for maximum unit
capacity. It is composed of a normally closed
solenoid valve (A), a normally open solenoid
valve (B), an internal pressure regulating valve.
With valves A and B both energized (A open, B
closed) during normal compressor operation,
high pressure oil is directed to the slide valve.
This pressure acts on the surface of the slide
valve piston creating a force which is sufficient
to overcome the opposing spring force and to
move the valve in the direction of increasing
capacity.
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