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Condenser Freeze Prevention —
gorithm helps prevent condenser tube freeze-up by energiz-
ing the condenser pump relay. If the pump is controlled by
the PIC, starting the pump will help prevent the water in the
condenser from freezing. Condenser freeze prevention can
occur whenever the machine is not running except when it
is either actively in pumpdown or in Pumpdown Lockout
with the freeze prevention disabled (refer to Control Test table,
Pumpdown/Terminate Lockout tables).
When the CONDENSER REFRIG TEMP is less than or
equal to the CONDENSER FREEZE POINT, or the EN-
TERING CONDENSER WATER temperature is less than or
equal to the CONDENSER FREEZE POINT, then the CON-
DENSER WATER PUMP shall be energized until the CON-
DENSER REFRIG TEMP is greater than the CONDENSER
FREEZE POINT plus 5° F (2.7° C). An alarm will be gen-
erated if the machine is in PUMPDOWN mode and CON-
DENSER FREEZE is active. An alert will be generated if
the machine is not in PUMPDOWN mode and CONDENSER
FREEZE is active.
Tower-Fan Relay —
ture can cause the chiller to shut down on low refrigerant
temperature. The tower fan relay, located in the starter, is
controlled by the PIC to energize and deenergize as the pres-
sure differential between cooler and condenser vessels changes
in order to prevent low condenser water temperature and to
maximize machine efficiency. The tower-fan relay can only
accomplish this if the relay has been added to the cooling
tower temperature controller. The TOWER FAN RELAY is
turned on whenever the CONDENSER WATER PUMP is run-
ning, flow is verified, and the difference between cooler and
condenser pressure is more than 30 psid (207 kPad) or en-
tering condenser water temperature is greater than 85 F
(29 C). The TOWER FAN RELAY is deenergized when the
condenser pump is off, flow is lost, the evaporator refriger-
ant temperature is less than the override temperature, or the
differential pressure is less than 28 psid (193 kPad) and en-
tering condensing water is less than 80 F (27 C).
IMPORTANT: A field-supplied water temperature con-
trol system for condenser water should be installed.
The system should maintain the leaving condenser wa-
ter temperature at a temperature that is 20° F (11° C)
above the leaving chilled water temperature.
The tower fan relay control is not a substitute for a con-
denser water temperature control. When used with a Wa-
ter Temperature Control system, the tower fan relay control
can be used to help prevent low condenser water tem-
peratures and associated problems.
Auto. Restart After Power Failure —
may be enabled or disabled, and may be viewed/modified in
the Config table of Equipment Configuration. If enabled, the
chiller will start up automatically after a single cycle drop-
out, low, high, or loss of voltage has occurred, and the power
is within ±10% of normal. The 15- and 1-minute inhibit tim-
ers are ignored during this type of start-up.
When power is restored after the power failure, and if the
compressor had been running, the oil pump will be ener-
gized for one minute prior to the evaporator pump energiz-
ing. Auto restart will then continue like a normal start-up.
This control al-
Low condenser water tempera-
This option
Water/Brine Reset —
brine reset are available and can be viewed or modified on
the Equipment Configuration table Config selection.
The LID default screen status message indicates when the
chilled water reset is active. The Control Point temperature
on the Status01 table indicates the machine's current reset
temperature.
To activate a reset type, input all configuration informa-
tion for that reset type in the Config table. Then input the
reset type number in the SELECT/ENABLE RESET TYPE
input line.
1. Reset Type 1 (Requires optional 8-input module) — Au-
tomatic chilled water temperature reset based on a 4 to
20 mA input signal. This type permits up to ±30° F
(±16° C) of automatic reset to the chilled water or brine
temperature set point, based on the input from a 4 to
20 mA signal. This signal is hardwired into the number
one 8-input module.
If the 4-20 mA signal is externally powered from the 8-input
module, the signal is wired to terminals J1-5(+) and
J1-6(–). If the signal is to be internally powered by the
8-input module (for example, when using variable resis-
tance), the signal is wired to J1-7(+) and J1-6(–). The PIC
must now be configured on the Service2 table to ensure
that the appropriate power source is identified.
2. Reset Type 2 (Requires optional 8-input module) — Au-
tomatic chilled water temperature reset based on a
remote temperature sensor input. This type permits
±30° F (±16° C) of automatic reset to the set point based
on a temperature sensor wired to the number one 8-input
module (see wiring diagrams or certified drawings).
The temperature sensor must be wired to terminal J1-19
and J1-20.
To configure Reset Type 2, enter the temperature of the
remote sensor at the point where no temperature reset will
occur. Next, enter the temperature at which the full amount
of reset will occur. Then, enter the maximum amount of
reset required to operate the machine. Reset Type 2 can
now be activated.
3. Reset Type 3 — Automatic chilled water temperature re-
set based on cooler temperature difference. This type of
reset will add ±30° F (±16° C) based on the temperature
difference between entering and leaving chilled water tem-
perature. This is the only type of reset available without
the need of the number one 8-input module. No wiring is
required for this type as it already uses the cooler water
sensors.
To configure Reset Type 3, enter the chilled water tem-
perature difference (the difference between entering and
leaving chilled water) at which no temperature reset oc-
curs. This chilled water temperature difference is usually
the full design load temperature difference. The differ-
ence in chilled water temperature at which the full amount
of reset will occur is now entered on the next input line.
Next, the amount of reset is entered. Reset Type 3 can
now be activated.
28
Three types of chilled water or
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