Product manual

IOMM ACR/AGR-1 71
Low Ambient Start
If the “LOW AMBIENT” option was selected and the out side air temperature is below 50°F, the low
ambient start logic will replace the normal starting logic. The compressor with the lowest starts on the
lead circuit will start when the liquid line solenoid valve is energized. The LPCutIn will be ignored and
the refrigerant freeze protect set point will be ignored for 180 seconds to allow time for the refrigerant
pressure to build. After the 180 second time and the evaporator pressure is below the freeze stat set
point, the circuit will shut down and the alarm “LoEvapPressure” will be indicated.
The chilled water freeze alarm set point is enforced during low ambient starts and will shut down the
chiller if a water freeze conditions is detected. During the low ambient start period, the evaporator
pressure is monitored and if the evap pressure drops to 2 psi for more than 20 seconds, the chiller will
shut off and a “LoEvap Pressure” alarm will be generated. This protects the compressor from
operating in a vacuum during start-up.
Pumpdown
As the system chilled water requirements diminish, the controller will stage down the compressors.
As the system load continues to drop, the liquid line solenoid valve will be de-energized and the
refrigerant circuit will go through a one time pump down sequence. As the evaporator pressure falls
below the LPCutOut set point, the compressor and condenser fan will stop. The evaporator pump
output relay will remain energized and the unit status will indicate “Waiting For Load”.