
FORM 160.81-O1 (1020)
ISSUE DATE 10/05/2020
13
JOHNSON CONTROLS
SECTION 1 - DESCRIPTION OF SYSTEM AND FUNDAMENTALS OF OPERATION
1
After the first 3 minutes of System Run and for the
remainder of System Run, if the Differential Discharge
Oil Pressure decreases to following threshold for 2
continuous seconds, a safety shutdown is performed
and “Oil – Low Differential Discharge Oil Pressure”
is displayed: [(evap press/10) +20] PSID with soft-
ware version C.OPT.05.09.303 and later or less than
[(evap pressure/10) +15] PSID with software version
C.OPT.05.08.303 and earlier.
After the first 3 minutes and for the remainder of Sys-
tem Run, the Minimum Load Control feature prevents
the slide valve from unloading to a point that will not
allow sufficient oil transfer to the Oil Separator. The
slide valve position at which insufficient oil transfer
occurs is based on compressor motor current. The op-
erating point at which the low separator oil level oc-
curs, can be found by manually unloading the slide
valve while observing the system conditions. Once
established, the minimum allowed slide valve posi-
tion is that which will maintain the compressor motor
current above the programmed Minimum Load FLA
(15% to 70%) setpoint. When the slide valve unloads
to the point the motor current decreases to the setpoint
value, no more unload pulses will be applied. If it un-
loads to the point where the motor current is less than
the setpoint, a 1 second load pulse is applied every 3
seconds until the motor current is more than or equal
to the Minimum Load FLA setpoint value. While the
slide valve unloading is being inhibited, “MINIMUM
LOAD – LOAD LIMIT” is displayed on the System
Details Line of the Display.
Later in 2007, new production chillers are equipped
with an oil level sensor in the Oil Separator. The Low
Separator Oil LED on the OIL SEPERATOR screen
indicates the oil level status. With sufficient level, it is
extinguished. With insufficient level, it is illuminated.
After the chiller has been running for at least 3 minutes,
if the level sensor opens for 30 continuous seconds,
a safety shutdown is performed and “Oil Separator –
Low Level” is displayed. The chiller can be restarted
after the COMPRESSOR switch is placed in the Stop-
Reset (O) position and sufficient oil has been added to
allow the Sensor to see sufficient level and provide a
closed circuit to the Microboard.
After the chiller has been running for more than 3 min-
utes, the slide valve is loaded and unloaded to control
the Leaving Chilled Liquid Temperature to the Leav-
ing Chilled Liquid Temperature setpoint (as explained
later, there is no unloading in Ice Storage mode). The
SENSITIVITY
setpoints can be adjusted by a Service
ant Level Control feature is enabled. If the Refriger-
ant Level Control feature is disabled, the duration is 30
seconds. If the Refrigerant Level Control is enabled,
the duration is programmable over the range of 30 to
300 seconds with the
Valve Preset Time
setpoint. The
Variable Orifice must be positioned to the 75% closed
position prior to starting the compressor motor. Since
it is in the fully open position while the chiller is shut-
down, the valve is driven to the 75% closed position
during the “Start Sequence Initiated” period. Due to
variances in Orifice actuator timing and valve position
requirements for the different chiller/compressor com-
binations, the “Start Sequence Initiated” period dura-
tion must be adjusted to allow the Orifice to reach the
75% closed position prior to starting the compressor
motor. “Start Sequence Initiated” is displayed on the
Display System Status Line along with a countdown
timer indicating time remaining while the period is in
effect.
During the first 15 seconds of the “Start Sequence
Initiated” period, early vintage chillers performed the
pressure transducer auto-zeroing. Beginning with soft-
ware versions C.OPT.05.09.303 (and later), the auto-
zeroing feature is no longer used. If applicable, refer to
description of this feature, as used in previous software
versions, in OptiView Control Center Service Instruc-
tions (Form 160.81-M1).
The Chilled Liquid Flow Switch position is checked
5 seconds before the end of the “Start Sequence Initi-
ated” period. If not closed, a cycling shutdown is per-
formed.
At the completion of the start sequence, the Oil Sup-
ply Solenoid Valve is energized (opened), “SYSTEM
RUN” is displayed and the start signal is applied to the
compressor motor starter.
When the Condenser
Pump Delay
setpoint (0 to 90
seconds) [software version C.MLM.05.06.xxx (and
later) or C.OPT.05.06.xxx (and later)] has elapsed,
condenser pump contacts TB2-150/151 close to start
the condenser pump.
During the first 2 minutes of System Run, a HOLD
output is applied to the slide valve. During the third
minute, if the oil pressure is less than or equal to
((1.1 x evaporator pressure) + 15 PSID), a load out-
put is applied to the slide valve until the oil pressure
is more than or equal to ((1.1 x evaporator pressure)
+ 18 PSID). Also during the first 3 minutes of “Sys-
tem Run”, the Variable Orifice position is maintained
at the 75% closed position and controlled thereafter as
described below.