Shunt Trip

The shunt trip funct ion of the PIC is a safe ty trip. The shunt t rip is wired from an o utput on the
SMM to the motor circuit breaker. If the PIC tries to shut down the compressor through normal
shutdown procedure but is unsuccessful for 30 s ec o nds, the shunt trip ou tp ut is energized and
causes the circuit brea ker to trip off. If groun d fa ult protection has be en ap plied to the starter ,
the ground fault trip wi ll al so energize the shunt tri p to trip the circuit br ea ker.
Default Screen Fr eez e
Whenever an alarm occurs, the LID default screen will freeze displaying the condition of the
machine at the time of alarm . Knowledge of the ope r at ing state of the chiller at the time an
alarm occurs is useful when troubleshooting. Current mach ine information can be viewe d on the
Status tables. Once all existing alarms are cleared (by pressing the RESET softkey), the default
LID will return normal op eration.
Motor Cooling Control
Motor temperature is re duc e d by refrigerant enter i ng the motor shell an d ev ap orating. The
refrigerant is regula ted by the motor cool ing relay. This re lay will energize wh en the compressor
is running and motor tempe rature is above 125 F (51 .7 C). The relay will clos e when motor
temperature is below 100 F (37.8 C). Note that there i s always a mi nimum flow of refrigerant
when the compressor is ope rating for motor coo lin g; the relay only contr ol s additional
refrigerant to the motor.