York MILLENNIUM YCAS Installation Operation & Maintenance page 17

cage flows into the rotors at a point about 1.2x suction.
This assures that a required minimum differential of at
least 2.0 bar (30 PSID) exists between discharge and
1.2x suction, to force oil into rotor case, a minimum of
0.6 bar (10 PSID) is all that is required to assure pro-
tection of the compressor. Oil pressure is measured as
the difference between suction pressure and the pres-
sure of the oil entering the rotor case.
Maximum working pressure of the oil separator is 31
bar (450 PSIG). A relief valve is installed in the oil sepa-
rator piping. This will soon be incorporated into the oil
separator. Oil level should be above the midpoint of the
"lower" oil sight glass when the compressor is running.
Oil level should not be above the top of the "upper"
sight glass. Oil temperature control is provided through
liquid injection activated by the microprocessor, utilizing
a discharge temperature sensor, and a solenoid valve.
Oil Cooling
Oil cooling is provided by routing oil from the oil separa-
tor through several rows of the condenser coils and back
to the compressor.
Capacity Control
The compressors will start at the minimum load position
and provide a capacity control range from 10% - 100%
of the full unit load using a continuous function slide
valve. The microprocessor modulates the current signal
to a 3-way pressure regulating capacity control valve
which controls compressor capacity independent of sys-
tem pressures and balances the compressor capacity
with the cooling load.
The automatic spring return of the capacity control valve
to the minimum load position will ensure compressor
starting at minimum motor load.
Loading is accomplished by varying pressure through
the capacity control valve to move the slide valve against
the spring pressure to provide stable, smooth loading.
Power and Control Panel
All controls and motor starting equipment are factory
wired and function tested. The panel enclosures are de-
signed to IP55 and are manufactured from powder
painted galvanized steel.
YORK INTERNATIONAL
The Power and Control Panel are divided into power
sections for each compressor and associated fans, a
control section and an electrical options section. The
power and control sections have separate hinged,
latched, and gasket sealed doors equipped with wind
struts.
Each power compartment contains:
Compressor and fan starting contactors, fan motor ex-
ternal overloads, control circuit serving compressor ca-
pacity control, compressor and fan contactor coils and
compressor motor overloads.
The current transformers for the compressor motor over-
loads sense each phase, as an input to the microproces-
sor. This protects the compressor motors from damage
due to: low current input, high input current, unbalanced
current, single phasing, phase reversal, and compressor
locked rotor.
The control section contains:
ON/OFF switch, microcomputer keypad and display, mi-
croprocessor board, I/O expansion board, relay boards
and power supply board.
The options sections contain:
A control circuit transformer complete with service
switch providing 115/1Ø power to the unit control sys-
tem.
Electrical options as described in "Accessories and
Options".
Microprocessor Controls
The microprocessor has the following functions and
displays:
• A liquid crystal 40 character display with text pro-
vided on two lines and light emitting diode back-
lighting outdoor viewing.
• A color coded, 35 button, sealed keypad with sec-
tions for Display, Entry, Setpoints, Clock, Print, Pro-
gram and Unit ON/OFF.
The standard controls shall include: brine chiIling, ther-
mal storage, automatic pump down, run signal contacts,
demand load limit from external building automation sys-
tem input, remote reset liquid temperature reset input,
FORM 201.18-NM2
2
17