YORK INTERNATIONAL
4
60Hz) to achieve the 45 PSID target oil pressure. The
target oil pressure remains 45 PSID throughout the
pre-lube period and during the first 15 seconds of com-
pressor run. While the target pressure is in effect,
OIL PRESSURE=XX.XPSID;TARGET=XX.X PSID
is displayed when the OIL PRESSURE display key is
pressed. As with the previous fixed speed oil pump ap-
plication, the compressor is started 50 seconds after the
chiller start is initiated.
After the compressor has been running for 15 seconds,
the target oil pressure becomes the “Oil Pressure
Setpoint” (20 to 45 PSID) that has been programmed
by the Service Technician using procedure under “Pro-
gramming”. The Micro Board then applies a speed
command to the VSOP drive that changes the output
frequency of the VSOP drive as required to achieve
this oil pressure. The programmed Oil Pressure
Setpoint is the oil pressure for the remainder of “SYS-
TEM RUN” and through “SYSTEM COASTDOWN”.
While the programmed Oil Pressure Setpoint is in
effect,
OIL PRESSURE=XX.X PSID; SETP=XX.X PSID
is displayed when the OIL PRESSURE key is pressed.
During oil pump operation, the actual oil pressure and
the frequency of the VSOP drive, is commanded to be
running and can be monitored with the DISPLAY DATA
key. One of the scrolled messages is
OIL PUMP VSD=XXX HZ;PRS=XX.XPSID
MICROCOMPUTER CONTROL CENTER
OPERATION
The Microcomputer Control Center maintains desired
system oil pressure by controlling the speed of the oil
pump. The speed at which the oil pump runs is deter-
mined by the VSOP drive output frequency. The Micro
Board applies a speed command to the VSOP drive to
control the output frequency. The speed command is in
the form of a Pulse Width Modulation (PWM) signal as
explained later.
During the Pre-Lube period and the first 15 seconds of
compressor run, the software in the Micro Board oper-
ates the VSOP drive over a range of 25 Hz to 60 Hz to
maintain the oil pressure at 45 PSID. Thereafter, it op-
erates the VSOP drive over this range to maintain the
oil pressure to the programmed “Oil Pressure
Setpoint” (20 to 45 PSID).
As with the fixed speed oil pump application, 13 sec-
onds after a chiller start is initiated, the oil pump is turned
on by a run signal from Relay Board TB3-29 (ref. Fig.
1). TB3-29 energizes new Relay 3R (instead of the oil
pump contactor as was previously done in the fixed
speed oil pump application). The closing of 3R contacts
applies a GROUND connection from Power Supply
Board J5-1 to the RUN input of the VSOP drive. This
starts the oil pump. The Micro Board applies a speed
command from J10-2 (through the Refrigerant Level
Control Board) to the VSOP drive’s “PWM” input that
ramps the VSOP drive output frequency from 25Hz to
whatever frequency is required (up to a maximum of
VARIABLE SPEED OIL PUMP DRIVE OPERATION - MODEL D CHILLER
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