Refrigerant Low - Low; Analog Inputs; High Limit Temperature; Freeze Temperature - Dometic SmartStart III Operation Manual

REFRIGERANT LOW – LOW SIDE PRESSURE LIMIT (Optional)
The PLC will immediately acknowledge an open circuit if the low pressure switch is tripped and de‐energize the compressor. It will
record and display low pressure fault on the alarm screen. If the PLC detects a low pressure fault during operation, a LP fault will be
displayed and recorded. The PLC will not allow the compressor relay to be re‐energized, until switch is in the closed position.
The fault must be manually acknowledged via the PLC and cleared prior to re‐enabling the system or stage.
ANALOG INPUTS
HIGH LIMIT TEMPERATURE SETPOINT
The high limit temperature sensor is continuously monitored whether in Cooling, Reverse Cycle or Electric Heat mode.
This sensor is used to detect a high temperature condition in the supply water from the chiller. If the chilled water temperature is sensed
to be greater or equal to 125°F (51.7°C), all enabled compressor relays will be de‐energized, turning off the compressor(s) if operating
in reverse cycle mode. If electric heat is being used, all enabled heater relays will be de‐energized, turning off the heating element(s).
As the temperature falls, the compressor or electric heat relay will re‐energize when the temperature reaches 110°F (43.3°C).
A high temperature fault will be recorded and displayed if the system exceeds the alarm set point. In a high temperature situation, PLC
will not allow the compressor or electric heat relay to be energized. The fault must be manually acknowledged on the active alarm
screen and cleared prior to re‐enabling the system or stage.
If a temperature sensor is bad or not connected, the PLC will display an alarm for that sensor.
FREEZE TEMPERATURE SETPOINT
The low limit temperature sensor is continuously monitored whether in Cooling, Reverse Cycle or Electric Heat mode.
This sensor is used to detect a freeze condition in the supply water of the chiller. If the chilled water temperature is sensed to be equal to
or less than 38°F (3.3°C), then the compressor relay will be de‐energized, shutting off the compressor. As the temperature rises, the
compressor relay will re‐energize when the temperature reaches 42°F (5.6°C).
A low temperature fault will be recorded and displayed if the system falls below the alarm set point. In a low temperature situation,
PLC will not allow the compressor or electric heat relay to be energized. The fault must be manually acknowledged on the active alarm
screen and cleared prior to re‐enabling the system or stage.
If a temperature sensor is bad or not connected, the PLC will display an alarm for that sensor.
Condenser Freeze Protection (Optional)
The system is equipped with a temperature sensor mounted to the condenser coil. This sensor is there to sense the coil temperature. In
heat mode if the coil temperature drops below 40 °F, the PLC controls will automatically lower the speed of the compressor to half the
speed that it was currently running. The display will indicate "Freeze Defrost" while performing this operation.
PRESSURE TRANSDUCERS
SUCTION Pressure
The suction pressure is continuously monitored by the PLC. If the suction pressure is below the alarm set point for longer than the
programmed time delay, a fault will occur. This low suction fault will be recorded and displayed on the alarm screen.
The fault must be manually acknowledged via the PLC and cleared prior to re‐enabling the system or stage.
DISCHARGE Pressure
The discharge pressure is continuously monitored by the PLC. If the discharge pressure is above the alarm set point for longer than the
programmed time, a fault will occur. This high pressure fault will be recorded and displayed on the alarm screen.
The fault must be manually acknowledged via the PLC and cleared prior to re‐enabling the system or stage.
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