York YD A, Operating & Maintenance, Page: 32 / 52

JOHNSON CONTROLS
32
FORM 160.69-O2
ISSUE DATE: 9/30/2020
SECTION 3 – SYSTEM COMPONENTS DESCRIPTION
OIL HEATER
During long idle periods, the oil in the compressor oil
reservoir tends to absorb as much refrigerant as it can
hold, depending upon the temperature of the oil and
the pressure in the reservoir. As the oil temperature is
lowered, the amount of refrigerant absorbed will be
increased. If the quantity of refrigerant in the oil be-
comes excessive, violent oil foaming will result as the
pressure within the system is lowered on starting. This
foaming is caused by refrigerant boiling out of the oil
as the pressure is lowered. If this foam reaches the oil
pump suction, the bearing oil pressure will fluctuate
with possible temporary loss of lubrication, causing the
oil pressure safety cutout to actuate and stop the sys-
tem. See “Control Center” Form 160.69-O1 .
MOTOR DRIVELINE
The compressor motor is an open-drip-proof, squir-
rel cage, induction type constructed to YORK design
specifications. 60 hertz motors operate at 3570 rpm. 50
hertz motors operate at 2975 rpm.
The open motor is provided with a D-flange, cast iron
adapter mounted to the compressor and supported by a
motor support.
Motor drive shaft is directly connected to the compres-
sor shaft with a flexible disc coupling. This coupling
has all metal construction with no wearing parts to as-
sure long life, and no lubrication requirements to pro-
vide low maintenance.
For units utilizing remote Electro-Mechanical starters,
a terminal box is provided for field connected conduit.
Motor terminals are brought through the motor cas-
ing into the terminal box. Jumpers are furnished for
three-lead type of starting. Motor terminal lugs are not
furnished. Overload/overcurrent transformers are fur-
nished with all units.
HEAT EXCHANGERS
Evaporator and condenser shells are fabricated from
rolled carbon steel plates with fusion welded seams.
Heat exchanger tubes are internally enhanced type.
The evaporator is a shell and tube, flooded type heat
exchanger. A distributor trough provides uniform dis-
tribution of refrigerant over the entire shell length.
Stainless steel mesh eliminators or suction baffles are
located above the tube bundle to prevent liquid refrig-
erant carryover into the compressor. A 2" liquid level
sight glass is located on the side of the shell to aid in
determining proper refrigerant charge. The evaporator
shell contains dual refrigerant relief valves.
The condenser is a shell and tube type, with a discharge
gas baffle to prevent direct high velocity impingement
on the tubes. A separate subcooler is located in the con-
denser to enhance performance. Dual refrigerant relief
valves are located on condenser shells with optional
isolation refrigerant isolation valves.
The removable compact water boxes are fabricated of
steel. The design working pressure is 150 PSIG (1034
kPa) and the boxes are tested at 225 PSIG (1551 kPa).
Integral steel water baffles provide the required pass
arrangements. Stub-out water nozzle connections with
Victaulic grooves are welded to the water boxes. These
nozzle connections are suitable for Victaulic couplings,
welding or flanges, and are capped for shipment.
Plugged 3/4" drain and vent connections are provided
in each water box.
REFRIGERANT FLOW CONTROL
Refrigerant flow to the evaporator is controlled by a
variable orifice.
A level sensor senses the refrigerant level in the con-
denser and outputs an analog voltage to the Microboard
that represents this level (0% = empty; 100% = full).
Under program control, the Microboard modulates a
variable orifice to control the condenser refrigerant
level to a programmed setpoint. Other setpoints affect
the control sensitivity and response. These setpoints
must be entered at chiller commissioning by a qualified
service technician. Only a qualified service technician
may modify these settings.
While the chiller is shut down, the orifice will be in the
fully open position causing the sensed level to be ap-
proximately 0%. When the chiller is started, after the
vane motor end switch (VMS) opens when entering
SYSTEM RUN
, if actual level is less than the level
setpoint, a linearly increasing ramp is applied to the
level setpoint. This ramp causes the setpoint to go from
the initial refrigerant level (approximately 0%) to the
programmed setpoint over a period of 15 minutes.
If the actual level is greater than the setpoint when the
VMS opens, there is no pulldown period, it immedi-
ately begins to control to the programmed setpoint.