JOHNSON CONTROLS
74
FORM 150.62-NM6 (103)
S Y S 1 H I G H D S C H P R E S
S Y S 2 H I G H D S C H P R E S
S Y S 1 L O W S U C T P R E S S
S Y S 2 L O W S U C T P R E S S
When this message appears, suction pressure limiting
is in effect. Suction Pressure Limiting is only available
on units that have the suction pressure transducer
installed. If a low pressure switch is installed instead,
suction pressure limiting will not function.
The suction pressure limit is a control point that limits
the loading of a system when the suction pressure drops
to within 15% above the suction pressure cutout. On a
standard system programmed for 44 PSIG/3.0 Bar suc-
tion pressure cutout, the micro would inhibit loading of
the affected system with the suction pressure less than
or equal to 1.15 * 44 PSIG/3.0 Bar = 50 PSIG/3.5 Bar.
The system will be allowed to load after 60 seconds
and after the suction pressure rises above the suction
pressure limit point.
This message indicates that load limiting is in effect and
the percentage of the limiting in effect. This limiting could
be due to the load limit/pwm input, ISN or RCC controller
could be sending a load limit command.
If MANUAL OVERRIDE mode is selected, the STATUS
display will display this message. This will indicate that
the Daily Schedule is being ignored and the chiller will
start-up when chilled liquid temperature allows, Remote
Contacts, UNIT switch and SYSTEM switches permitting.
This is a priority message and cannot be overridden by
anti-recycle messages, fault messages, etc. when in the
STATUS display mode. Therefore, do not expect to see
any other STATUS messages when in the MANUAL
OVERRIDE mode. MANUAL OVERRIDE is to only be
used in emergencies or for servicing. Manual override
mode automatically disables itself after 30 minutes.
The PUMPING DOWN message indicates that a com-
pressor in the respective system is presently in the pro-
cess of pumping the system down. When pumpdown
is initiated on shutdown, the liquid line solenoid or EEV
will close and a compressor will continue to run. When
the suction pressure decreases to the suction pressure
cutout setpoint or runs for 180 seconds, whichever
comes rst, the compressor will cycle off.
FAULT STATUS MESSAGES
Safeties are divided into two categories – system
safeties and unit safeties. System safeties are faults
that cause the individual system to be shut down. Unit
safeties are faults that cause all running compressors
to be shut down. Following are display messages and
explanations.
System Safeties:
System safeties are faults that cause individual systems
to be shut down if a safety threshold is exceeded for 3
seconds. They are auto reset faults in that the system
will be allowed to restart automatically after the fault
condition is no longer present. However, if 3 faults on
the same system occur within 90 minutes, that system
will be locked out on the last fault. This condition is then
a manual reset. The system switch (under OPTIONS
key) must be turned off and then back on to clear the
lockout fault.
The Discharge Pressure Cutout is a software cutout in
the microprocessor and is backed-up by a mechanical
high pressure cutout switch located in the refrigerant
circuit. It assures that the system pressure does not
exceed safe working limits. The system will shutdown
when the programmable cutout is exceeded and will be
allowed to restart when the discharge pressure falls 40
PSIG below the cutout. Discharge transducers must be
installed for this function to operate.
The Suction Pressure Cutout is a software cutout that
helps protect the chiller from an evaporator freeze-up
should the system attempt to run with a low refrigerant
charge or a restriction in the refrigerant circuit.
Repeated starts after resetting a low suc-
tion pressure fault will cause evaporator
freeze-up. Whenever a system locks out
on this safety, immediate steps should
be taken to identify the cause.
At system start, the cutout is set to 10% of pro-
grammed value. During the next 3 minutes the cutout
point is ramped up to the programmed cutout point.
If at any time during this 3 minutes the suction pres-
sure falls below the ramped cutout point, the system
will stop.
S Y S 1 S U C T L I M I T I N G
S Y S 2 S U C T L I M I T I N G
S Y S 1 L O A D L I M I T X X %
S Y S 2 L O A D L I M I T X X %
M A N U A L
O V E R R I D E
S Y S 1 P U M P I N G D O W N
S Y S 2 P U M P I N G D O W N
Unit Controls
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