Shutdown Sequence; Automatic Soft Stop Amps Threshold; Chilled Water Recycle Mode; Safety Shutdown - Carrier 19XR Start-Up, Operation And Maintenance Instructions Manual

Shutdown Sequence —
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, COM-
PRESSOR DEENERGIZED'' is displayed, and the com-
pressor ontime and service ontime stop. The guide vanes are
then brought to the closed position. The oil pump relay and
the chilled water/brine pump relay shut down 60 seconds
after the compressor stops. The condenser water pump shuts
down at the same time if the ENTERING CONDENSER
WATER temperature is greater than or equal to 115 F
(46.1 C) and the CONDENSER REFRIG TEMP is greater
than the CONDENSER FREEZE POINT plus 5 F (−15.0 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% af-
ter shutdown, or the starter contacts remain energized, the
oil pump and chilled water pump remain energized and
the alarm is displayed.
• The condenser pump shuts down when the CONDENSER
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
3° F (−1.6° C).
• If the chiller shuts down due to low refrigerant tempera-
ture, the chilled water pump continues to run until the LEAV-
ING CHILLED WATER temperature is greater than the
CONTROL POINT temperature, plus 5° F (3° C).
Automatic Soft Stop Amps Threshold —
stop amps threshold feature closes the guide vanes 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 guide vanes close to a
preset amperage percent until the guide vane is less than
4% open or 4 minutes have passed. The compressor then
shuts off.
If the chiller enters an alarm state or if the compres-
sor 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
INCREASE or DECREASE softkey to set the SOFT
STOP 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,
COMPRESSOR UNLOADING'' displays on the CVC.
The soft stop amps threshold function can be terminated
and the compressor motor deenergized immediately by de-
pressing the STOP button twice.
Chiller shutdown begins if
The soft
Chilled Water Recycle Mode —
off and wait until the load increases to restart when
the compressor is running in a lightly loaded condition. This
cycling is normal and is known as recycle. A recycle shut-
down is initiated when any of the following conditions
are true:
• the chiller is in LCW control, the difference between the
LEAVING CHILLED WATER temperature and ENTER-
ING CHILLED WATER temperature is less than the
RECYCLE SHUTDOWN DELTA T (found in the
SETUP1 table) and the LEAVING CHILLED WATER tem-
perature is below the CONTROL POINT, −5 F (−15.0 C)
the CONTROL POINT has not increased in the last 5 min-
utes and ICE BUILD is not active.
• the ECW CONTROL OPTION is enabled, the difference
between the ENTERING CHILLED WATER temperature
and the LEAVING CHILLED WATER temperature is less
than the RECYCLE SHUTDOWN DELTA T (found in the
SETUP1 table), and the ENTERING CHILLED WATER
temperature is below the CONTROL POINT −5 F
(−15.0 C) and the CONTROL POINT has not increased in
the last 5 minutes.
• the LEAVING CHILLED WATER temperature is within
3° F (2° C) of the EVAP REFRIG TRIPPOINT.
When the chiller is in RECYCLE mode, the chilled water
pump relay remains energized so the chilled water temper-
ature can be monitored for increasing load. The recycle
control uses RECYCLE RESTART DELTA T to check when
the compressor should be restarted. This is an operator-
configured function which defaults to 5° F (3° C). This value
can be viewed or modified on the SETUP1 table. The com-
pressor will restart when the chiller is:
• in LCW CONTROL and the LEAVING CHILLED
WATER temperature is greater than the CONTROL POINT
plus the RECYCLE RESTART DELTA T.
• in ECW CONTROL and the ENTERING CHILLED
WATER temperature is greater than the CONTROL POINT
plus the RECYCLE RESTART DELTA T.
Once these conditions are met, the compressor initiates a
start-up with a normal start-up sequence.
An alert condition may be generated if 5 or more recycle
start-ups occur in less than 4 hours. Excessive recycling can
reduce chiller life; therefore, compressor recycling due to
extremely low loads should be reduced.
To reduce compressor recycling, use the time schedule to
shut the chiller down during known low load operation
period, or increase the chiller load by running the fan sys-
tems. If the hot gas bypass is installed, adjust the values to
ensure that hot gas is energized during light load condi-
tions. Increase the RECYCLE RESTART DELTA T on the
SETUP1 table to lengthen the time between restarts.
The chiller should not be operated below design mini-
mum load without a hot gas bypass installed.
Safety Shutdown —
a manual shutdown with the exception that, during a safety
shutdown, the CVC displays the reason for the shutdown,
the alarm light blinks continuously, and the spare alarm con-
tacts are energized.
After a safety shutdown, the RESET softkey must be
pressed to clear the alarm. If the alarm condition is still present,
the alarm light continues to blink. Once the alarm is cleared,
the operator must press the CCN or LOCAL softkeys to
restart the chiller.
45
The chiller may cycle
A safety shutdown is identical to