Unit installation

IOMM ACZ/AGZ-3 ACZ / AGZ-BM 67
risen above the unload setpoint, another compressor will be stopped. The last compressor on a
circuit will not stop due to the unload condition.
High Condenser Pressure
If the discharge pressure rises above the High Condenser Pressure Unload setpoint, and more than
one compressor on the circuit is running, the circuit will stage down. One compressor will
shutdown as soon as the pressure rises above the unload setpoint, and if two remain running, then
one more will shut down 10 seconds later, if the pressure is still above the unload setpoint. No stage
up will be allowed on the circuit until the condenser pressure drops to the unload setpoint, less 100
psi, and the outdoor ambient temperature drops 5 degrees F.
Low Ambient Lockout
If the OAT drops below the low ambient lockout setpoint, then all running circuits will do a normal
stop. Once the lockout has been triggered, no compressors will start until the OAT rises to the
lockout setpoint plus 5 degrees F.
High Ambient Limit
On units not configured with multi-point power connections, the maximum load amps could be
exceeded at high ambient temperatures. If all circuit 1 compressors are running or all but one
compressor on circuit 1, power connection is single point, and the OAT is greater than 116°F, circuit
2 is limited to running all but one compressor. The circuit 2 status will indicate if this is the case.
This action will allow the unit to operate at higher temperatures than 116°F.
Unit Capacity Overrides
The following conditions override the automatic capacity control when the chiller is in COOL mode
only.
Demand Limit
The maximum unit capacity 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 maximum unit capacity
stage is determined as shown in the following graphs:
Maximum LWT Rate
The maximum rate at which the leaving water
temperature can drop is limited at all times by the
Maximum Rate setpoint. If the rate exceeds this
setpoint, no more compressors will be started until
the pulldown rate is less than the setpoint.
1
2
3
4
0.0 25.0 50.0 100.075.0
Max
Stage
3
4
5
6
0 16.7 66.7 83.350.0
Limit Signal (%)
Max
Stage
33.3 100.0
2
1
0
Limit Signal (%)
Limit Signal vs. Max Stage
(with 4 compressors)
Limit Signal vs. Max Stage
(with 6 compressors)