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

The Suction Temperature Limiting message applies only
when the chiller is set for Water Cooling Mode (see
page 113). The message indicates that saturated suc-
tion temperature on a system has dropped to -2°C (29ºF)
and that any further temperature reduction could cause
some icing of the evaporator tubes. Saturated suction
temperature is computed by the micro by converting
suction pressure to temperature.
For the first 3 minutes that the saturated suction tem-
perature is at or below -2°C (29ºF) any further compres-
sor loading is inhibited to allow time for the temperature
to rise. If the condition persists for more than 3 minutes,
a 5 minute timer is started. As this timer counts down to
zero, a 1 second unload pulse will be sent to the slide
valve of the affected compressor every 5 seconds as
long as the temperature is below -1°C (31ºF). If the tem-
perature rises above -1°C (31ºF), the micro will inhibit
loading for the remainder of the 5 minute period.
If, after the 5 minute period, the saturated suction tem-
perature is above -2°C (29ºF), the compressor is allowed
to reload, if required, to maintain leaving chilled water.
Otherwise, the micro will reset the 5 minute timer and
start the process over again. To assure that leaving chilled
water requirements are satisfied while one compressor
is under Suction Temperature Limiting control, the micro
will start or load other compressor(s) as necessary.

2.5 UNIT FAULT STATUS MESSAGES

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.
YORK INTERNATIONAL
Low Ambient Temperature Cutout:
U N I T
L O W A M B I E N T
The Low Ambient Temperature Safety protects the
chiller from running in very low temperatures which
could cause damage due to low system pressures. This
feature is programmable and can also be used to shut
down the chiller at a temperature where continued run-
ning of the chiller is not economical compared to the
use of "free" cooling techniques (see also Section 8.2 /
Low Ambient Temperature Cutout [page 137]). The
fault will clear when ambient temperature rises 1°C
(12ºF) above the cut-out.
High Ambient Temperature Cutout:
U N I T
H I G H A M B I E N T
The High Ambient Temperature Safety protects the
chiller from running in ambients above 54°C (130ºF)
where potential malfunction of system mechanical and
electrical components may result. The High Ambient
Cutout is programmable and can be set for lower limit
values if required (see also Section 8.2 / High Ambient
Temperature Cutout [page 137]). The fault will clear
when ambient temperature drops 1°C (2ºF) below the
cut-out.
Low Leaving Chilled Liquid Temperature
Cutout:
U N I T
L O W L I Q U I D
The Low Water Temperature Safety assures that the
evaporator is not damaged from freezing due to improp-
erly set control points. It also attempts to protect the
chiller from freezing, if the flow switch should fail.
Whenever the chilled liquid temperature drops below
the programmable cutout, the chiller will shut down (see
also Section 8.2 / Leaving Water Temperature Cutout,
page 138). The chiller fault will clear when temperature
rises 2°C (4ºF) above the cut-out and cooling demand
exists.
FORM 201.18-NM2
F A U L T
T E M P
F A U L T
T E M P
F A U L T
T E M P
111
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