York YD A, Operating & Maintenance, Page: 29 / 52

JOHNSON CONTROLS
29
FORM 160.69-O2
ISSUE DATE: 9/30/2020
3
SECTION 3 – SYSTEM COMPONENTS DESCRIPTION
GENERAL
The YORK Model YD Centrifugal Liquid Chiller is
completely factory-packaged including evaporator,
condenser, 2 compressors, 2 motors, lubrication sys-
tem, OptiView™ Control Center, and all interconnect-
ing unit piping and wiring.
COMPRESSOR
Each compressor is a single-stage centrifugal type
powered 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
bellows cartridge style with ceramic internal and
atmospheric seal faces. The seal is oil-flooded at all
times and is pressure-lubricated during operation.
CAPACITY CONTROL
Pre-rotation vanes (PRV) in each compressor modu-
late chiller capacity from 100% to 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 leav-
ing chilled liquid temperature. Rugged airfoil shaped
cast manganese bronze vanes are precisely positioned
by solid vane linkages connected to the electric actua-
tor.
Both compressors are operated when needed to satisfy
the building load. At loads below 50%, a single com-
pressor is able to handle the load more efficiently.
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 motor-
compressor which must be supplied with forced lubri-
cation 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 re-
verse).
2.
Compressor Driven Shaft (High Speed)
a. Forward and reverse high speed thrust bear-
ing.
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 for each compressor is
located in a common 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.