Condenser Pump Control; Condenser Freeze Prevention; Tower Fan Relay Low And High; Auto. Restart After Power Failure - Carrier AquaEdge 23XRV Start-Up, Operation And Maintenance Instructions Manual

Troubleshooting Guide, Checking Display Messages, page 97.
After the alarm has been reset the PIC III controls will incre-
ment the Starts in 12 Hours counter by one upon restart. If the
limit of 8 starts in a 12-hour period occurs Prestart Alert 100
must be manually reset at the local chiller control panel
(ICVC).
Condenser Pump Control —
tor the condenser pressure (CONDENSER PRESSURE) and
may turn on the condenser pump if the condenser pressure
becomes too high while the compressor is shut down. The
condenser pressure override (COND PRESS OVERRIDE)
parameter is used to determine this pressure point. COND
PRESS OVERRIDE is found in the SETUP1 display screen,
which is accessed from the EQUIPMENT SERVICE table.
The default value is 145 psig (543 kPa).
If the CONDENSER PRESSURE is greater than or equal to
the COND PRESS OVERRIDE, the condenser pump will ener-
gize to try to decrease the pressure and Alert 151 will be gener-
ated. The pump will turn off when the condenser pressure is
less than the COND PRESS OVERRIDE threshold.
Condenser Freeze Prevention —
rithm helps prevent condenser tube freeze-up by energizing the
condenser pump relay through terminals 3 and 4 of the hazard-
ous voltage terminal strip (TB2) in the control center. The
PIC III module controls the pump and, by starting it, helps to
prevent the liquid in the condenser from freezing. The PIC III
module can perform this function whenever the chiller is not
running except when it is either actively in pumpdown or in
pumpdown/lockout with the freeze prevention disabled.
When the CONDENSER REFRIG TEMP is less than or
equal to the CONDENSER FREEZE POINT, the CONDENS-
ER LIQUID PUMP is energized until the CONDENSER
REFRIG TEMP is greater than the CONDENSER FREEZE
POINT plus 5º F (2.7º C) and the ENTERING CONDENSER
LIQUID TEMPERATURE is greater than or equal to the
CONDENSER FREEZE POINT. An alarm (244) is generated
if the chiller is in PUMPDOWN mode and the pump is ener-
gized. An alert (154) is generated if the chiller is not in PUMP-
DOWN mode and the pump is energized. If the chiller is in
RECYCLE SHUTDOWN mode, the mode will transition to a
non-recycle shutdown.
Tower Fan Relay Low and High —
er liquid temperature can cause the chiller to shut down if it
causes the condenser refrigerant temperature to be too low. The
tower fan relays, located on terminals 5-8 on the hazardous
voltage terminal strip (TB2) in the control center, are controlled
by the PIC III module to energize and de-energize as the pres-
sure differential between cooler and condenser vessels chang-
es. This prevents excessively low condenser liquid tempera-
tures. The tower fan relay can only accomplish this if the relay
has been added to the cooling tower temperature controller.
The tower fan relay low is turned on whenever the condens-
er liquid pump is running, flow is verified, the difference
between cooler and condenser pressure is more than 30 psid
(207 kPad), and the ENTERING CONDENSER LIQUID
temperature is greater than 65 F (18.3 C).
The tower fan relay low is turned off when the CONDENS-
ER LIQUID PUMP is deenergized, when CONDENSER
LIQUID FLOW indication is lost, or under the following
conditions:
1. CALC EVAP SAT TEMP is less than EVAP SAT
OVERRIDE TEMP.
2. The difference between the CONDENSER PRESSURE
and EVAPORATOR PRESSURE is less than 25 psi
(172 kPa).
The tower fan relay high is turned on whenever the
condenser liquid pump is running, flow is verified and the
The chiller will moni-
This control algo-
Low condens-
53
difference between cooler and condenser pressure is more than
35 psid (241.3 kPa) for ENTERING COND LIQUID
temperature greater than the TOWER FAN HIGH SETPOINT
(SETPOINT menu, default 75 F [24 C]).
The tower fan relay high is turned off when the condenser
pump is off, flow is stopped, or the CALC EVAP SAT TEMP is
less than the EVAP SAT OVERRIDE TEMP and ENTERING
CONDENSER LIQUID is less than 70 F (21.1 C), The tower
fan relay high is also turned off when the difference between
CONDENSER PRESSURE and EVAPORATOR PRESSURE is
less than 28 psid (193 kPa), and ENTERING CONDENSER
LIQUID temperature is less than TOWER FAN HIGH SET-
POINT minus 3° F (1.6° C).
The TOWER FAN RELAY LOW and HIGH parameters are
accessed from the STARTUP screen.
IMPORTANT: A field-supplied liquid temperature control
system for condenser liquid should be installed. The system
should maintain the leaving condenser liquid temperature at
a temperature that is 20º F (11º C) above the leaving chilled
liquid temperature.
CAUTION
The tower fan relay control is not a substitute for a con-
denser liquid temperature control. When used with a liquid
temperature control system, the tower fan relay control can
be used to help prevent low condenser liquid temperatures
that may damage equipment.
Auto. Restart After Power Failure —
may be enabled or disabled and may be viewed or modified on
the OPTIONS screen, which is accessed from the SERVICE
table. If the AUTO. RESTART option is enabled, the chiller will
start up automatically after a power failure has occurred (after a
single cycle dropout; low, high, or loss of voltage; and the
power is within ±10% of normal). The 15 and 3-minute inhibit
timers are ignored during this type of start-up.
When power is restored after the power failure, a power
failure restart will be enabled and the control allowed to
AUTORESTART the chiller, starting with the chilled liquid
pump(s), if start-up conditions are met.
If power to the ICVC module has been off for more than
3 hours or the timeclock has been set for the first time, the
compressor will start with the slowest temperature-based ramp
load rate possible in order to minimize oil foaming.
Fast Power Source Transfers —
cal system is being prepared to transfer power from utility
power to generator power or from generator power back to util-
ity power, and the power transfer is an open transition type, and
time to transfer is less than 5 seconds, the chiller should be
stopped before the transfer occurs and restarted after the trans-
fer has been completed. If the chiller is not stopped before the
transfer occurs, alarms on the chiller can occur that must be
manually reset, such as a circuit breaker trip. To accomplish
shutdown and restart automatically, a set of dry contacts should
be opened 30 to 60 seconds before the transfer occurs, then
closed after the transfer is complete to restart the chiller. The
contacts must be wired to the to the Remote START/STOP
contact in the starter or VFD (see the field wiring diagrams,
pages 130-144) and the Remote Start contact configuration
must be enabled. If power transfers take 5 seconds or longer,
the chiller Auto Restart after Power Failure feature (if enabled)
will automatically restart the chiller.
Liquid/Brine Temperature Reset —
chilled liquid or brine setpoint temperature reset are available
and can be viewed or modified on the TEMP_CTL screen,
which is accessed from the EQUIPMENT SERVICE table.
This option
When the electri-
Three types of