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JOHNSON CONTROLS
122
SECTION 7 - OPERATION
FORM 201.28-NM1.1
ISSUE DATE: 1/31/2018
The HPCO is wired in series with the VSD Run
Signal and will only be checked by the Chiller
Control Board when the system is running. The
mechanical cutout opens at 23.2 barg ± 0.55 barg (337
PSIG ± 8 PSIG) and closes at 17.4 barg ± 0.69 barg
(252 PSIG ± 10 PSIG). The Status display fault mes-
sage for this system is shown below:
SYS X YYYYYYYY HPCO FAULT
The X indicates the system and YYYYYYY indicates
the system is in a “FAULT” condition and will restart
when the 120 second anti-recycle timer times out or
“LOCKOUT” and will not restart until the operator
clears the fault using the keypad.
Low Suction Pressure Cutout (Software) Fault
The programmable Low Suction Pressure Cutout is
a secondary back-up for the flow switch and protects
against operation with low refrigerant charge, which
helps protect the chiller from an evaporator freeze-up,
should the system attempt to run with a low refrigerant
charge. The Status display fault message for this cut-
out is shown below:
SYS X YYYYYYYY LOW SUCTION PRESSURE
The X indicates the system and YYYYYYY indicates
the system is in a “FAULT” condition and will restart
when the 120 second anti-recycle timer times out or
“LOCKOUT” and will not restart until the operator
clears the fault using the keypad. Typically, the cutout
will be set at 1.65 barg (24 PSIG) for chilled water ap-
plications.
The cutout is ignored for the first 30 seconds of system
run time. During the next 3 minutes of run time the
cutout point is linearly ramped from 10% of the cutout
value up to the programmed cutout point. If at any time
during the first 3 minutes of operation the suction pres-
sure falls below the ramped cutout point, the system
will shut down with a controlled ramped shutdown.
The cutout pressure during operating periods of 30 sec-
onds to 210 seconds is ramped and can be calculated by
the following:
After the first 3 minutes and 30 seconds of run time, if
the suction pressure falls below the cutout as a result
of a transient in the system, a transient timer is set at
30 seconds and a linearly ramped cutout is set start-
ing at 10% of the programmed cutout. If over the next
30 seconds, the suction pressure does not stay above
the ramped cutout, which ramps between 10% of the
cutout and the programmed cutout over the 30 second
period, the system will fault on low suction pressure.
Low Motor Current Cutout Fault
The Motor Current Cutout shuts the system down with
a controlled ramped shutdown when the microprocessor
detects the absence of motor current (less than 10% FLA),
usually indicating that a compressor is not running. This
safety is ignored for the first 10 seconds of operation.
The status display fault message for this safety is
shown below:
SYS X YYYYYYYY LOW MOTOR CURRENT
The X indicates the system and YYYYYYY indicates
the system is in a “FAULT” condition and will restart
when the 120 second anti-recycle timer times out or
“LOCKOUT” and will not restart until the operator
clears the fault using the keypad.
High Differential Oil Pressure Cutout Fault
The High Differential Oil Pressure Cutout protects the
compressor from low oil flow and insufficient lubrica-
tion, possibly from a dirty oil filter. A system will fault
and shut down with a controlled ramped shutdown
when its Discharge to Oil Differential Pressure rises
above the cutout of 4.48 barg (65 PSID). This safety is
ignored for the first 90 seconds of run time. This safety
measures the pressure differential between discharge
and oil pressure, which is the pressure drop across the
oil filter. The Status display fault message for this safe-
ty is shown below:
SYS X YYYYYYYY HIGH DIFF OIL PRESSURE
The X indicates the system and YYYYYYY indicates
the system is in a “FAULT” condition and will restart
when the 120 second anti-recycle timer times out or
“LOCKOUT” and will not restart until the operator
clears the fault using the keypad.
Low Differential Oil Pressure Cutout Fault
The Low Differential Oil Pressure Cutout protects the
compressor from low oil flow and insufficient lubrica-
tion. A system will fault and shut down with a controlled
ramped shutdown when it’s differential between oil
and suction pressure falls below the cutout. This safety
assures that the compressor is pumping sufficiently to