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After 225 seconds of operation with suction pressure
operating above the cut-out, a 30 second transient timer
prevents short term fluctuations in suction pressure due
to loading or fan cycling from causing shutdown. If
suction pressure drops below the cutout point after 225
seconds of operation, the transient timer is activated.
While the transient timer is active, suction pressure must
not drop below 10% of the cut-out initially programmed
and must be greater than:
C.O. = Programmed C.O. X ( Time + .1 )
This transient cutout value increases with time until after
30 seconds it equals the programmed cutout value. If the
suction pressure falls below the value as calculated by
the formula relative to time, the system will shut down
on a low suction pressure fault. If the suction pressure
rises above the programmed cutout value, the 30 second
timer will be reset.
If the Dip Switch on the microprocessor board is set for
"Water Cooling" (see page 142), the cutout is program-
mable between 44 - 70 PSIG (3-5 bar) for both R-22 and
R407C models. In this mode, settings of 44 PSIG (3 bar)
for R-22 and R407C are recommended. If the Switch is
set for "Brine Cooling" (glycol) the cutout is program-
mable between 5 - 70 PSIG (0.3 - 5 bar) for R-22 and
R407C models. In this mode, the cutout should typically
be set to the saturated refrigerant pressure equivalent to
18°F (10°C) below the temperature of the chilled liquid.
The sludge point of the glycol MUST be
at least 20°F (11°C) below the equivalent
cutout temperature. This programmable
value is password protected.
High Compressor Motor Current Cutout:
S Y S
#
H I G H
S Y S
#
H I G H
The High Motor Current Safety protects against ex-
cessively high motor current and shuts a system down
and locks it out after only a single occurrence of a rise
in average motor current above the cutout point. Motor
current is monitored using 3 Current Transformers (CTs)
per motor, one on each phase.
140
33.3
M T R
C U R R
M T R
C U R R
Average motor current is monitored after 7 seconds of
compressor operation. The system will be shut down if
average motor current exceeds 115% FLA.
FLA (full load amps) is approximately
1.2 x RLA (rated load amps). RLA is
specified on the motor / chiller name‑
plate and is typical current demand
under rated operating conditions in
a fully loaded system. When a system
is fully loaded, typical motor currents
may be at 60 ‑ 85% FLA depending on
operating conditions.
Low Motor Current Cutout / Motor Protector (Hi
Motor Winding Temp Cutout) / Mechanical High
Pressure Cutout / External Motor Overload:
S Y S
#
L O W
S Y S
#
L O W
The Low Motor Current Safety prevents a compressor
motor running with less current than would normally be
expected. This may result from loss of refrigerant, con-
tactor, or power problems as well as from a compressor
that is not pumping due to a mechanical malfunction.
Motor current is monitored using 3 Current Transformers
(CTs) per motor, one on each phase.
Average motor current is monitored after 3 seconds of
compressor operation. From this time the system will
be shut down if average motor current is less than 10%
of FLA.
Compressor Motor Protection Modules, External
Motor Overloads and Mechanical High Pressure
Cutouts are fitted to each system. All these devices
stop the compressor by removing power from its motor
contactor coils. This causes the CTs to obviously sense a
zero current draw by the compressor motor and causes a
Low Motor Current Fault to be displayed. These devices
operate as follows:
The Motor Protection Module protects against exces-
sive motor winding temperature by monitoring 3 or 6
sensors built into the motor windings. If the temperature
becomes excessive, the module will cause power to be
C U R R / M P / H P
C U R R / M P / H P
JOHNSON CONTROLS
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