Unit installation

68 ACZ / AGZ-BM IOMM ACZ/AGZ-3
Pumpdown
When a circuit reaches a condition where it needs to shut down normally, a pumpdown cycle will be
performed. All but the lowest numbered running compressor will shut off. During pumpdown, the
hot gas bypass and liquid line valves are closed, while a compressor continues to run. The
pumpdown is complete when the evaporator pressure is less than the low evaporator pressure unload
setpoint, less 15 psi, or the circuit has been in the pumpdown state for 60 seconds.
Standard Condenser Fan Control
Stage Up Compensation
In order to create a smoother transition when another fan is staged on, the VFD compensates by
slowing down initially. This is accomplished by adding the new fan stage up deadband to the VFD
target. The higher target causes the VFD logic to decrease fan speed. Then, every 10 seconds, 0.5
degree F is subtracted from the VFD target until it is equal to the saturated condenser temperature
target setpoint. This will allow the VFD to slowly bring the saturated condenser temperature back
down.
Fantrol
Condenser Fans Staging is based on condenser pressure as selected by Fan Stage On & Off
setpoints. Fans 1, 3, 5, and 7 are for circuit 1, and fans 2, 4, 6, and 8 are for circuit 2. Fans 1 and 2
start with the first compressor on the respective circuit when the ambient temperature is greater than
75°F. Below 75°F, these fans start when the condenser pressure gets up to the stage on setpoint. The
compressor must be running in order to run any fans.
Fan Stages
There are 2, 3, or 4 fans available per circuit. On 8 fan units, fans 5/7 and 6/8 are controlled by one
contactor for each pair, using virtual stages to allow a difference of only one fan between stages.
See the tables below:
4 and 6 Fan Units
Stage (3-Fan) Fans On Cir. 1 Fans On Cir. 2
1 1 2
2 1,3 2,4
3 1,3,5 2,4,6
8 Fan Units
Stage (2&4-Fan) Fans On Cir 1 Fans On Cir. 2
1 1 2
2 1,3 2,4
3 1,5,7 2,6,8
4 1,3,5,7 2,4,6,8
Normal Operation - Staging Up
At startup, the first fan will start when the saturated condenser temperature rises above the target.
After this, the stage up deadbands apply.
When the saturated condenser temperature is above the Target + the active deadband, a Stage Up
error is accumulated.