OMM 1008-1
27
MANUAL. Of the following limits, the one creating the lowest amp limit is in effect. The resulting present
limit value for compressor current is stored in the Active Demand Limit variable.
Low Evaporator Pressure
If the evaporator pressure drops below the Low Evaporator Pressure – Inhibit setpoint, the unit will inhibit
capacity increase. If the evaporator pressure drops below the Low Evaporator Pressure - Unload setpoint, the
unit will begin capacity decrease.
High Discharge Temperature - Load
If the discharge temperature rises above the High Discharge Temperature - Load setpoint and the motor
current is < 50% RLA, the unit will begin capacity increase.
Soft Load
Soft Loading is a configurable function used at compressor startup to limit the maximum current draw on the
compressor in a ramp-up type manner. It is only active on the first compressor to start. The setpoints that
control this function are:
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Soft Load – (ON/OFF)
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Begin Amp Limit – (%RLA)
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Maximum Amps – (%RLA)
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Soft Load Ramp – (seconds)
The active soft load limit value (in % RLA) increases linearly from the Begin Amp Limit setpoint to the
Maximum Amps setpoint over the amount of time specified by the Soft Load Ramp setpoint. If the amp draw
rises above the currently active soft load limit value, the unit will inhibit capacity increases. If the amp draw
rises to 5% or more above this value, the unit will begin capacity decrease.
Maximum LWT Rate
The maximum rate at which the leaving water temperature can drop (chiller mode = COOL) is limited at all
times by the Maximum Rate setpoint. If the rate exceeds this setpoint, capacity increases is inhibited.
Demand Limit
The maximum amp draw of the compressor can be limited by a 4 to 20 mA signal on the Demand Limit
analog input. This function is only enabled if the Demand Limit setpoint is set to ON. The amp limit
decreases linearly from the Maximum Amp Limit setpoint (at 4 mA) to the Minimum Amp Limit setpoint (at
20mA). If the amp draw rises above the limit value, the unit will inhibit capacity increases. If the amp draw
rises to 5% or more above this value, the unit will begin capacity decrease.
Network Limit
The maximum amp draw of the compressor can be limited by a value sent through a BAS network connection
and stored in the Network Limit variable. If the amp draw rises above the limit value, the unit will inhibit
capacity increases. If the amp draw rises to 5% or more above this value, the unit will begin capacity
decrease.
Minimum Amp Limit
The minimum amp draw of the compressor can be limited by the Minimum Amps setpoint. If the amp draw
drops below the limit value, the unit will inhibit capacity decrease.
Maximum Amp Limit
The maximum amp draw of the compressor is always limited by the Maximum Amps setpoint. This limit has
priority over all other functions including manual capacity control. If the amp draw rises above the limit
value, the unit will inhibit capacity increases. If the amp draw rises to 5% or more above this value, the unit
will begin capacity decrease.
