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Min Suct Press
The Minimum Suction Pressure setpoint
serves two purposes. When the condensing unit
is operating in Refrigeration mode using the
Temperature strategy, the Minimum Suction
Pressure is the suction pressure at which the
compressor will be shut off regardless of the
case circuit temperature. This setpoint is neces-
sary as a safety feature since the CUB is control-
ling by temperature instead of by suction
pressure.
If you enabled the Pump Down delay feature
for this CUB, the Minimum Suction Pressure
also acts as the termination setpoint for the pump
down delay. The Pump Down delay period will
end when the suction pressure falls below this
setpoint.
7.3.2.1.
Temperature Differential (TD)
TD setpoint
The temperature differential setpoint is the
minimum allowable difference between the
refrigerant drop leg temperature and the ambient
(plenum) temperature. When the TD (i.e., drop
leg temp + drop leg offset - plenum temp) begins
to climb above this setpoint, fans will be cycled
ON to bring down the drop leg temperature (thus
lowering the TD measurement).
TD deadband
The temperature differential deadband is a
range of values around the TD Setpoint within
which the value of the TD calculation is accept-
able. When the TD rises above the setpoint plus
1/2 the deadband value, fans will begin cycling
ON. When the TD falls below the setpoint minus
1/2 the deadband value, fans will cycle OFF.
Drop Leg Max
The Drop Leg Max setpoint is the maximum
allowable value of the drop leg temperature. If
the drop leg temperature rises above this set-
point, the CUB will cycle condenser fans ON
regardless of the value of the TD.
30 • MultiFlex CUB-II and CUB-TD I&O Guide
Drop Leg Min
The Drop Leg Min setpoint is the minimum
allowable value of the drop leg temperature. If
the drop leg temperature falls below this set-
point, the CUB will cycle condenser fans OFF
regardless of the value of the TD.
Cond Fan On Dly
If using TD control, the CUB cycles fans ON
when the TD is above the setpoint at the rate set
in the Cond Fan On Dly field. In other words, if
this field is set to 30 seconds, then the CUB-II
will stage each fan ON in 30-second intervals
until all fans are ON or until the TD falls back
below the setpoint.
Cond Fan Of Dly
If using TD control, the CUB cycles fans
OFF when the TD is below the setpoint at the
rate set in the Cond Fan Of Dly field. In other
words, if this field is set to 30 seconds, then the
CUB will stage each fan OFF in 30-second inter-
vals until all fans are OFF or until the TD rises
back above the setpoint.
7.3.2.2.
Traditional Strategy
Fan 1 Cut In
Fan 1 Cut In sets the activation setpoint for
condenser fan #1. When the discharge pressure
rises above the Cut In setpoint, the fan will turn
ON.
Fan 1 Cut Out
Fan 1 Cut Out sets the deactivation setpoint
for condenser fan #1. When the discharge pres-
sure falls below the Cut Out setpoint, the fan will
turn OFF.
Fan 1 Minimum ON Time
The Fan 1 Minimum ON time is the smallest
amount of time condenser fan #1 must remain
ON after being activated.
Fan 2 Cut In
Fan 2 Cut In sets the activation setpoint for
condenser fan #2. When the discharge pressure
rises above the Cut In setpoint, the fan will turn
ON.
026-1705 Rev 7 06-APR-2010
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