48
If the water/brine temperature is high enough, the start-up
sequence continues and checks the slide valve unload timer. If
the unload timer has expired, the PIC II then confirms the cor-
rect refrigerant type by comparing the cooler and condenser
refrigerant temperature to the leaving water temperature for
each vessel. If the refrigerant and leaving water temperatures
are within 15 F (8 C) for each respective vessel, compressor
start relay (1CR) energizes to start the compressor.
Compressor ontime and service ontime timers start, and the
compressor starts in 12 hours counter and the number of starts
over a 12-hour period counter advance by one.
Failure to verify any of the requirements up to this point will
result in the PIC II aborting the start and displaying the applica-
ble pre-start mode of failure on the CVC default screen. A pre-
start failure does not advance the starts in 12 hours counter.
Any failure after the 1CR relay has energized results in a safety
shutdown, advances the starts in the12 hours counter by one,
and displays the applicable shutdown status on the CVC
display.
Shutdown Sequence —
Chiller shutdown begins if
any of the following occurs:
• the STOP button is pressed for at least one second (the
alarm light blinks once to confirm the stop command)
• a recycle condition is present (see Chilled Water Recycle
Mode section)
• the time schedule has gone into unoccupied mode
• the chiller protective limit has been reached and chiller
is in alarm
• the start/stop status is overridden to stop from the CCN
network or the CVC
When a stop signal occurs, the shutdown sequence first
stops the compressor by deactivating the start relay (1CR).
A status message of “SHUTDOWN IN PROGRESS,
COMPRESSOR DEENERGIZED” is displayed, and the com-
pressor ontime and service ontime stop.
The slide valve unload timer is activated for 2 minutes to
move the slide valve to an open position. When the slide valve
unload timer expires, compressor start relay (1CR) is deener-
gized. The cooler water pump is shut down 30 seconds later.
The condenser pump is also shut down if the
ENTERING
CONDENSER WATER
temperature is greater than or equal to
115 F (46.1) and the
CONDENSER REFRIG TEMP
is greater
than the
CONDENSER FREEZE POINT
plus 5 F (3 C). The
stop-to-start timer now begins to count down. If the start-to-
start timer value is still greater than the value of the start-to-
stop timer, then this time displays on the CVC.
Certain conditions that occur during shutdown can change
this sequence.
• If the
AVERAGE LINE CURRENT
is greater than 15%
after shutdown, or the starter contacts remain energized,
the chilled water pump remains energized and the alarm
is displayed.
• The condenser pump shuts down when the
CON-
DENSER PRESSURE
is less than the
CONDENSER
PRESSURE OVERRIDE
threshold minus 3.5 psi (24.1
kPa) and the
CONDENSER REFRIG TEMP
is less than
or equal to the
ENTERING CONDENSER WATER
temperature plus 3º F (1.6º C).
• If the chiller shuts down due to low refrigerant tempera-
ture, the chilled water pump continues to run until
the
LEAVING CHILLED WATER
temperature is greater
than the
CONTROL POINT
temperature, plus 5º F
(3º C).
Automatic Soft Stop Amps Threshold —
The soft stop amps threshold feature closes the slide valve of
the compressor automatically if a non-recycle, non-alarm stop
signal occurs before the compressor motor is deenergized.
If the STOP button is pressed, the slide valve unloads to a
preset amperage percent, or the slide valve timer expires. The
compressor then shuts off.
If the chiller enters an alarm state or if the compressor enters
a RECYCLE mode, the compressor deenergizes immediately.
To activate the soft stop amps threshold feature, scroll to the
bottom of OPTIONS screen on the CVC. Use the
or softkey to set the SOFTSTOP AMPS
THRESHOLD parameter to the percent of amps at which the
motor will shut down. The default setting is 100% amps (no
soft stop). The range is 40 to 100%.
When the soft stop amps threshold feature is being applied,
a status message, “SHUTDOWN IN PROGRESS, COM-
PRESSOR UNLOADING” displays on the CVC.
INCREASE
A—START INITIATED: Pre-start checks are made; evaporator pump
started
B—Condenser water pump started (5 seconds after A)
C—Water flows verified (30 seconds to 5 minutes maximum)
D—Chilled water temperature checked against control point; tower fan
control enabled; slide valve decrease timer checked to verify slide
valve position
E—Refrigerant type verified (up to 3 minutes after D).
F—Compressor motor starts; phase reversal conditions monitored; com-
pressor ontime and service ontime start; 15-minute inhibit timer starts
(10 seconds after E)
G—Shutdown initiated: Compressor motor stops; compressor ontime and
service ontime stop; 3-minute inhibit timer starts on PSIO Software
Version 8 and 12 and 1-minute inhibit timer on PSIO Software Version
13 and higher; slide valve decrease activated for 1 minute
H—Evaporator pump deenergized (30 seconds after G); condenser
pump and tower fan control may continue to operate if condenser
pressure is high; evaporator pump may continue if in RECYCLE
mode
I—Slide valve decrease timer expires (3 minutes after G)
O/A — Restart permitted (both inhibit timers expired) (minimum of 15 min-
utes after F; minimum of 1 minute after G)
Fig. 29 — Control Sequence
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