IOMM AGZ-3 AGZ 035A through 065A 59
Manual Operation
Manual operating modes are available to simplify setup and troubleshooting of the unit. Any of the
following manual modes can 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 AGZ Scroll chiller has two (2) refrigerant circuits and each circuit has two (2) scroll
compressors. 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 with the lowest number of starts in the other refrigerant circuit. Stage 3 of cooling will
start the next compressor with the lowest number of starts regardless of refrigerant circuit. Stage 4
will start the last compressor.
If a compressor is not available for starting due to an equipment equipment protection control, the
number of cooling stages will be decreased and always equal to the number of available compressors
for operation. At all times 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 start the other 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.
On a stage down (4 compressors operating), the compressor with the most run hours will be stopped.
The next stage down will be the compressor on the other refrigerant circuit with the most run hours.
The next stage down will be the compressor with the most run hours.
Head Pressure Control
There are two 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 (230 psig 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 290 psig (R-
22 setpoint) and remain on until minimum lift pressure regains control.
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