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will be locked out on the last fault. This condition is
then a manual reset. The system switch (under OP-
TIONS 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 ex-
ceed safe working limits. The system will shutdown
when the programmable cutout is exceeded and will be
allowed to restart when the discharge pressure falls be-
low the cutout. Discharge transducers must be installed
for this function to operate.
The Suction Pressure Cutout is a software cutout that
protects the unit from an evaporator freeze-up should
the system attempt to run with a low refrigerant charge
or a restriction in the refrigerant circuit.
At system start, the cutout is set to 10% of programmed
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 pressure falls
below the ramped cutout point, the system will stop.
This cutout is ignored for the first 90 seconds of system
run time to avoid nuisance shutdowns, especially on
units that utilize a low pressure switch in place of the
suction pressure transducer.
After the first 3 minutes, if the suction pressure falls
below the programmed cutout setting, a “transient pro-
tection routine” is activated. This sets the cutout at 10%
of the programmed value and ramps up the cutout over
the next 30 seconds. If at any time during this 30 sec-
onds the suction pressure falls below the ramped cut-
out, the system will stop. This transient protection
scheme only works if the suction pressure transducer is
installed. When using the mechanical LP switch, the
operating points of the LP switch are: opens at 23 PSIG
+/- 5 PSIG (1.59 barg +/- .34 barg), and closes at 35
PSIG +/- 5 PSIG (2.62 barg +/- .34 barg).
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
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
If MANUAL OVERRIDE mode is selected, the STA-
TUS display will display this message. This will indi-
cate that the Daily Schedule is being ignored and the
unit will start-up when demand is present, Remote Con-
tacts, 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 MANUAL
OVERRIDE mode.
MANUAL OVERRIDE is to only be used in emergen-
cies or for servicing. Manual override mode automati-
cally 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, the liquid line solenoid will close and a com-
pressor will continue to run. When the suction pressure
decreases to the suction pressure cutout setpoint, the
compressor will cycle off. If pump down cannot be
achieved three minutes after the liquid line solenoid
closes, the compressor will cycle off.
FAULT STATUS MESSAGES
Safeties are divided into two categories - system safe-
ties and unit safeties. System safeties are faults that
cause the individual system to be shut down. Unit safe-
ties are faults that cause all running compressors to be
shut down. Following are display messages and expla-
nations.
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
Содержание MILLENNIUM YCUL0016SC
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