Chiller Shutdown Sequence; Control Points - Carrier AquaEdge 23XRV Controls Operation And Troubleshooting

START-UP
After a successful pre-start check, the chilled water pump relay is
energized. Condenser pump relay is turned on 5 seconds after the
evaporator pump relay.
Five seconds later, the control monitors the chilled water and con-
denser water flow devices to confirm water flow.
After water flow is verified, the water temperature is compared to
Setpoint +Recycle Shutdown Offset. If the temperature is less than
or equal to this value, the control turns off the condenser pump re-
lay and goes into RECYCLE mode.
If the RECYCLE condition is not satisfied, the start-up sequence
continues. Oil pump and, if applicable, main EXV initiate start se-
quence and a start signal will be given to the oil pump relay.
The oil pump and a oil pressure of 18 psid followed by 20s of pre-
lube will have to be achieved for the compressor to start
The Ramp loading feature in General Configuration controls
the rate at which the compressor loads up. Ramp loading can
be controlled either by temperature, amp, or kilowatts and the
desired ramp rate per minute for either can be configured. This
can prevent the compressor to load up too fast while the chilled
liquid loop is brought down to the set point.

Chiller Shutdown Sequence

Chiller shutdown begins if any of the following occurs:
• Local Stop Unit button is pressed.
• A RECYCLE condition is present. (See "RECYCLE CON-
TROL" on page 18.)
• The time schedule has gone into unoccupied mode as de-
fined in the Schedule Menu for either Local or Dual Stpt
Schedule (for AutoStart).
• The chiller protective limit has been reached and chiller is
in alarm.
• The start/stop status (CHIL_S_S) is overridden to stop
from the network when in AutoStart mode.
• If a loss of communication between the PIC6 and the VFD
occurs the run permissive relay will energize to start a
shutdown sequence.
NOTE: If any safety stop command is active the chiller will per-
form a hard shutdown and trip the Safety Stop alarm. Safety stop
can be triggered from the local Home Screen E-stop icon (red Stop
Button) or Network E-Stop point. The unit will not restart until the
Safety Stop command and alarm are cleared.
When a stop signal occurs, the controls set Target VFD Speed to 0.
This will cause the compressor to reduce speed to the point where
line amps equal the configured Soft Stop Threshold (Configura-
tion, Service Configuration = default 50%). At that point, or one
minute after the stop signal occurs (whichever is earlier), the VFD
is set to Stop. When the VFD is set to Stop, the compressor is
turned off.
When the compressor shut down is verified, the oil pump is turned
off and VFD STOP is complete. The pumps are deactivated at
least 30 seconds after the compressor is Off (for recycle shut down
the evaporator pump will remain on).
If the shutdown is due to low evaporator refrigerant temperature,
the chilled liquid pump continues to run until the leaving chilled
liquid temperature is high enough in an effort to prevent freeze-up.
When a non-recycle, non-alarm shutdown is called for, the soft
stop feature unloads the compressor by reducing speed to the point
where load amps equal the Soft Stop Threshold at which point the
compressor is turned off. If the chiller enters an alarm state or if
the compressor enters a RECYCLE mode, the compressor deener-
gizes immediately.
COMPRESSOR STOPPING
If a hard stop is requested, such as any E-stop command, the sys-
tem will remove the compressor request immediately and turn off
all running compressors. Otherwise, the system will ramp com-
pressor down.
OIL PUMP AND EXV (AS APPLICABLE) STOPPING
Once compressor is stopped, circuit performs oil and EXV stop-
ping. The following actions will be executed:
• Initialize Oil Pump stop sequence
• Initialize Oil Heater, Oil Vaporizer Heater, and Oil Re-
claim Valve stop sequence
• Initialize EXV stop sequence
CONDENSER PUMP STOPPING
Once all the above have stopped, the circuit executes. Once con-
denser pump is stopped at least 30 seconds after the circuit, stop-
ping is done.
EVAPORATOR PUMP STOPPING
The evaporator pump must then remain active anytime compres-
sor operation is possible, or there is an active Evaporator freeze
Alarm/Alert.
When chiller is shutting down, the Evaporator Pump is deactivat-
ed at least 30 seconds after the Compressor is off.

Control Points

SET POINT
The set point can be configured at the Setpoint menu, user access
level). The set point is determined by Cooling LCW Setpoint, but
can be configured for entering water temperature control by en-
abling the EWT Control Option in which it is controlled by the
Cooling ECW Setpoint value. See Fig. 34. The 23XRV chiller is
not suited for Ice Build.
Fig. 34 — Setpoint Menu, User Access Level
RECYCLE CONTROL
The chiller may cycle off and wait until the load increases to re-
start when the compressor is running in a lightly loaded condition.
This normal cycling is known as "recycle."
In cooling mode, a recycle shutdown is initiated when the follow-
ing conditions are true:
• Leaving chilled water temperature (or entering chilled wa-
ter temperature, if the EWT CONTROL OPTION is en-
abled) is more than 5°F [2.8°C]) below the CONTROL
POINT.
• Leaving chilled water temperature (or entering chilled wa-
ter temperature) is below the CONTROL POINT, and the
chilled water temperature difference is less than the Recy-
cle Shutdown Offset (default 5°F (2.8°C).
NOTE: Recycle shutdown will not occur if the CONTROL
POINT has been changed by more than 1°F (0.56°C) within the
previous 5 minutes of operation.
When the chiller is in RECYCLE mode, the chilled water
pump relay remains energized so the chilled water temperature
18