Carrier 17/19EX - Manual (Page 89)

CONDENSER FREEZE POINT , then the CONDENSER WATER PUMP shall be energized
until the CONDENSER REFRIG TEMP is greater than the CONDENSER FREEZE POINT plus
5° F (2.7° C). An alarm will be generated if the machine is in PUMPDOWN mode and the pump
is energized. An alert will be generated if the machine is not in PUMPDOWN mode and the
pump is energized. If in recycle shutdown, the mode shall transition to a non-recycle shutdown.
Tower-Fan Relay
This control can be used to assist the condenser water temperature control system (field
supplied). Low condenser water temperature 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 pressure 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 running, flow is verified, and the difference between cooler
and condenser pressure is more than 30 psid (207 kPad) or entering 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 refrigerant temperature is less than the
override temperature, or the differential pressure is less than 28 psid (193 kPad) and entering
condensing water is less than 80 F (27 C).