Section 3 - System Components Description; General; Compressor; Capacity Control - York R-134a Operation And Maintenance Manual

FORM 160.76-O1
ISSUE DATE: 05/22/2019

SECTION 3 - SYSTEM COMPONENTS DESCRIPTION

GENERAL

The YORK Model YK Centrifugal Liquid Chiller is
completely factory-packaged including evaporator,
condenser, compressor, motor, lubrication system, Op-
tiView™ Control Center, and all interconnecting unit
piping and wiring.

COMPRESSOR

The compressor is a single-stage centrifugal type pow-
ered by an open-drive electric motor.
The rotor assembly consists of a heat-treated alloy steel
drive shaft and impeller shaft with a cast aluminum,
fully shrouded impeller. The impeller is designed for
balanced thrust and is dynamically balanced and over-
speed tested. The inserted type journal and thrust bear-
ings are fabricated of aluminum alloy. Single helical
gears with crowned teeth are designed so that more
than one tooth is in contact at all times. Gears are inte-
grally assembled in the compressor rotor support and
are film lubricated. Each gear is individually mounted
in its own journal and thrust bearings.
The open-drive compressor shaft seal is a double bel-
lows cartridge style with ceramic internal and atmo-
spheric seal faces. The seal is oil-flooded at all times
and is pressure-lubricated during operation.

CAPACITY CONTROL

Pre-rotation vanes (PRV) modulate chiller capacity
from 100% to as low as 15% of design for normal air
conditioning applications. Operation is by an external,
electric PRV actuator which automatically controls the
vane position to maintain a constant leaving chilled liq-
uid temperature.

COMPRESSOR LUBRICATION SYSTEM

The chiller lubrication system consists of the oil pump,
oil filter, oil cooler and all interconnecting oil piping
and passages. There are main points within the com-
pressor which must be supplied with forced lubrication
as follows:
1. Compressor Drive Shaft (Low Speed)
a. Shaft seal.
b. Front and rear journal bearings – one on each
side of driving gear.
c. Low speed thrust bearing (forward and reverse).
JOHNSON CONTROLS
2. Compressor Driven Shaft (High Speed)
a. Forward and reverse high speed thrust
bearing.
b. Two journal bearings.
3. Speed Increasing Gears
a. Meshing surfaces of drive and pinion gear
teeth.
To provide the required amount of oil under the neces-
sary pressure to properly lubricate these parts, a motor
driven submersible oil pump is located in a remote oil
sump.
Upon pressing of the COMPRESSOR START switch
on the Control Center, the oil pump is immediately en-
ergized. After a 50 second pre-lube period, the com-
pressor motor will start. The oil pump will continue to
run during the entire operation of the compressor, and
for 150 seconds during compressor coastdown.
The submerged oil pump takes suction from the sur-
rounding oil and discharges it to the oil cooler where
heat is rejected. The oil flows from the oil cooler to
the oil filter. The oil leaves the filter and flows to the
emergency oil reservoir where it is distributed to the
compressor bearings. The oil lubricates the compressor
rotating components and is returned to the oil sump.
There is an emergency oil reservoir located at the high-
est point in the lubrication system internally in the com-
pressor. It provides an oil supply to the various bear-
ings and gears in the event of a system shutdown due
to power failure. The reservoir, located on the top of
the compressor, allows the oil to be distributed through
the passages by gravity flow, thus providing necessary
lubrication during the compressor coastdown.

OIL PUMP

For normal operation, the oil pump should operate at
all times during chiller operation.
On shutdown of the system for any reason, the oil
pump operates and continues to run for 150 seconds.
The system cannot restart during that time interval.
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