Carrier 19XL - Manual (Page 88)

Condenser Freeze Prevention
This control algorithm helps prevent condenser tube freeze-up by energizing 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 ENTERING CONDENSER WATER temperature is less than or equal to the
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
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