Unit Fault Status Messages - York MILLENNIUM YCAR0315 Installation Operation & Maintenance

iting" message if a limit is exceeded. To prevent the
controls from ever requiring a forced unload, the micro
anticipatory control will prevent a system from loading
when a limit exceeds 90% of the programmed unload
point. No display will indicate anticipatory loading pre-
vention. Loading will resume when the temperature/pres-
sure limit drops below 90% of the programmed limit.
Displays of anticipation safety control messages and
their meanings are as follows:
Discharge Pressure Limiting:
S Y S # D S C H
S Y S # D S C H
Discharge Pressure Limiting takes effect when com-
pressor discharge pressure nears the point at which the
high pressure cutout would shut the system down. When
the above message appears, discharge pressure has ex-
ceeded the programmable threshold and the compres-
sor loading is inhibited or is being unloaded in an effort
to prevent shutdown on the high pressure cutout. The
operation of this safety is important if condenser coils
become dirty, if there is a problem with the condenser
fan operation, or if extreme ambient or load conditions
occur (see Section 9 [8.2] / High Discharge Pressure
Unload Point [page 143] for more details).
Loading will take place when pressure drops below 90%
of the programmed unload point.
Compressor Motor Current Limiting:
S Y S # C U R R
S Y S # C U R R
The Motor Current Limiting message indicates that a
compressor motor current has reached a programmable
limit and the system loading is inhibited or is being un-
loaded to ensure that motor current does not become
excessively high, causing a fault (see also Section 9 [8.2]/
High Motor Current Unload Point, page 145; Section 9
[3.5]/, Motor Current Key, page 123; Section 9 [1.10],
page 107).
Loading will take place when current drops below 90%
of the unload point.
Suction Temperature Limiting:
S Y S # S U C T
S Y S # S U C T
YORK INTERNATIONAL
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The Suction Temperature Limiting message indicates
that saturated suction temperature on a system has
dropped to -4.4°C (24°F), and that any further tempera-
ture reduction could cause some icing of the evaporator
tubes. Saturated suction temperature is computed by the
micro by converting suction pressure to temperature.
When this threshold is exceeded, the micro will unload
the respective system. Reloading will take place when
temperature rises above the unload point plus 10%.
ISN Motor Current Limiting:
S Y S # I S N
S Y S # I S N
The ISN Motor Current Limiting message indicates that
a compressor motor current has reached a BAS limit and
the system is being unloaded according to a Building Au-
tomation System demand limit from the RS-485 input.
EMS-PWM Motor Current Limiting:
S Y S # E M S
S Y S # E M S
The EMS-PWM Motor Current Limiting message indi-
cates that a compressor motor current has reached a
programmable, BAS or Remote limit and the system is
being unloaded according to a demand limit signal pro-
vided from the PWM input or BAS board in the micro
panel.

2.5 UNIT FAULT STATUS MESSAGES

(AUTO RESET)
A Unit Fault will shut the entire chiller down when a
preset safety threshold is exceeded. The chiller will au-
tomatically restart after the condition causing the shut-
down clears. Restart will occur only after anti-recycle
timers are satisfied and cooling demand requires addi-
tional cooling. A reset hysteresis is built into each safety
so repetitive faulting and clearing will not occur in a
short time period.
Continuous monitoring by the microprocessor assures
that instantaneous reactions result. When the chiller is
shut down on one of these safeties, a message will ap-
pear on the Status display informing the operator of the
problem as shown in the text that follows.
Any time that a Unit Fault occurs, the shutdown will be
logged into the HISTORY BUFFER.
FORM 150.52-NM2 (1001)
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