Unit installation

66 ACZ / AGZ-BM IOMM ACZ/AGZ-3

Ice timer status (12 hours between starts)

Stage Up

For 2 compressors/circuit:

Control band = Evap Delta T x .3

For 3 compressors/circuit:

Control band = Evap Delta T x .2

[LWT Error > Startup_Delta_T_SP + 0.5(Control band)

AND Number Comps Running = 0

AND Ice Timer Expired]

THEN Stage_Up_Now = YES

ELSE IF

[LWT Error > 0

AND Number Comps Running > 0

AND Stage Up Timer Expired]

THEN Stage_Up_Now = YES

Stage Down

IF LWT Error < 0

THEN Stage_Down_Now = YES

Leaving Water Reset

The leaving water reset input uses a 4-20mA signal to reset the leaving water setpoint to a higher

value. The adjustment varies linearly from 0 degrees F to 10 degrees F, with a reset of 0 for a 4mA

signal and a reset of 10 for a 20mA signal.

At all times, the active leaving water setpoint is limited to a maximum of 60°F. The reset remains

proportional within the 10 degree band, but the setpoint will simply stop resetting when it reaches

the maximum.

Circuit Capacity Overrides – Limits of Operation

The following conditions override the automatic capacity control when the chiller is in COOL mode

or ICE mode. These overrides keep a circuit from entering a condition in which it is not designed to

run.

Low Evaporator Pressure

If a circuit is running, and the evaporator pressure drops below the Low Evaporator Pressure-Hold

setpoint, no more compressors will be allowed to start on that circuit. This limit is active until the

evaporator pressure reaches the hold setpoint plus 8 psi.

If a circuit is running with two or three compressors on, and the evaporator pressure drops below the

Low Evaporator Pressure-Unload setpoint, the circuit will begin reducing capacity. If two

compressors are running, one of the running compressors will be stopped. If three compressors are

running, then one compressor will be stopped initially. Ten seconds later, if the pressure has not