70 AGR 055A through 100A IOMM AGR
Manual Operation
Manual operating modes are available to simplify setup and troubleshooting of the unit. Any of the
following manual modes may be selected from the Control Mode Menu.
Note: These manual settings are intended to aid in troubleshooting and should not be
considered to be normal operating modes. The equipment should not be left unattended
during manual operation as the automatic staging controls are disabled. The chiller will
remain in the manual mode until Automatic operation is selected or a problem alarm occurs
which will change back to the “Automatic mode”.
• ManualOff: Manual unit off.
• Auto1Off2: Automatic Circ#1, Circ#2 off.
• Auto2Off1: Automatic Circ#2, Circ#1 off.
• ManualStaging: Manual Staging, Circ#1 & 2.
Compressor Staging
The AGR Reciprocating chiller has two refrigerant circuits and each circuit has one reciprocating
compressor. When in the Automatic mode and stage 1 of cooling is required, the compressor with
the lowest number of starts will be the first compressor to start. Stage 2 of cooling will start the
compressor in the other refrigerant circuit. Stages 3 through 6 will cause the compressors to load all
cyclinders.
If a compressor is not available for starting due to a safety, the number of cooling stages will be
decreased. In normal operation the second stage of cooling will have a compressor from each
refrigerant circuit operating. The exception to this is when “LOW AMBIENT” is selected and the
outside air temperature is below the low ambient setting. The staging logic will be modified to start
the compressor with the lowest starts and stage 2 will load the compressor on that refrigerant circuit.
Both compressors on one refrigerant circuit will operate at low ambient to improve head pressure
control. If additional cooling is required, the next refrigerant circuit will be started.
Head Pressure Control
There are two or three condenser fans per refrigerant circuit. These fans are cycled on and off
according to the circuit’s condenser pressure. Fan #1 of circuit will start when a compressor in the
circuit has started and the condenser pressure exceeds fan on setpoint (230psig R-22). This fan will
not cycle off until the circuit is stopped. The second fan will cycle on and off to maintain minimum
lift pressure. If the condenser pressure increases rapidly, the second fan will be turned on at 290psig
(R-22 setpoint) and remain on until minimum lift pressure regains control. The third fan will
operate based on the minimum lift pressure control.
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