Unit installation

100 ACZ / AGZ-BM IOMM ACZ/AGZ-3
Evaporator Fan Interlock
The Evap Fan can be cycled by the controller. If the unit is enabled and at least one circuit is able to
run, the controller sends a signal to start the fan (wired from terminals #33 and #35 on TB1). If air-
flow is sensed from an air flow switch or auxiliary contact (wired to terminals #44 and #61 on TB1)
for a settable time interval (10 second default value), the unit will be ready to start at a call for
cooling. On DX air handlers, this output and input do not have to be used, in which case a jumper is
required across terminals #44 and #61.
If a water chiller is used as the low side with the condensing unit, the flow switch interlock is
mandatory to help avoid an evaporator freeze-up resulting from no flow. Starting and stopping the
pump from the MicroTech II control is not mandatory.
Pumpdown
When a circuit reaches a condition where it needs to shut down normally, a pumpdown 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.
Condenser Fan Control
VFD
Condenser pressure trim control is accomplished using an optional low ambient fan VFD to control
the speed of the first fan on each circuit. This VFD control uses a proportional integral function to
drive the saturated condenser temperature to a target value by changing the fan speed. The target
value is normally the same as the saturated condenser temperature target setpoint.
The fan VFD always starts when the saturated condenser temperature rises higher than the target.
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 resetting the VFD target to the saturated condenser
temperature at the time of the stage up. The higher target causes the VFD logic to decrease fan
speed. Then, every five 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 reaches 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:
Table 58, Fan Staging
4 and 6 Fan Units 8 Fan Units
Stage Fans On Cir 1 Fans On Cir 2 Stage Fans On Cir 1 Fans On Cir 2
1 1 2 2 1,3 2,4
2 1,3 2,4 3 1,5,7 2,6,8
3 1,3,5 2,4,6 4 1,3,5,7 2,4,6,8