JOHNSON CONTROLS
119
SECTION 7 – UNIT CONTROLS
FORM 150.27-NM1
ISSUE DATE: 09/30/2015
7
The Holiday schedule must be programmed weekly.
Once the Holiday schedule runs, it will revert to the
normal Daily Schedule.
Program Key
There are several operating parameters under the PRO-
GRAM key that are programmable. These setpoints
can be changed by pressing the PROGRAM key, and
then the ENTER/ADV key to enter Program Mode.
Continuing to press the ENTER/ADV key will display
each operating parameter. While a particular parameter
is being displayed, the ↑ (UP) and ↓ (DOWN) arrow
keys can be used to change the value. After the value is
changed, the ENTER/ADV key must be pressed to en-
ter the data into memory.
shows
the programmable limits and default values for each
operating parameter.
Following are the displays for the programmable val-
ues in the order they appear:
d
D I S C H A R G E P R E S S U R E
C U T O U T = 5 7 0 P S I G
DISCHARGE PRESSURE CUTOUT is the discharge
pressure at which the system will shutdown as moni-
tored by the optional discharge transducer. This is a
software shutdown that acts as a backup for the me-
chanical high pressure switch located in the refrigerant
circuit. The system can restart when the discharge pres-
sure drops 40 PSIG (2.76 barg) below the cutout point.
If the optional discharge pressure transducer is not in-
stalled, this programmable safety would not apply. It
should be noted that every system has a mechanical
high pressure cutout that protects against excessive
high discharge pressure regardless of whether or not
the optional discharge pressure is installed.
S U C T I O N P R E S S U R E
C U T O U T = 80 . 0 P S I G
The SUCTION PRESSURE CUTOUT protects the
chiller from an evaporator freeze-up. If the suction
pressure drops below the cutout point, the system will
shut down. Typically, the cutout should be set to 80
PSIG (5.52 Bars) form water cooling.
There are some exceptions when the suc-
tion pressure is permitted to temporarily
drop below the cutout point. Details are
explained under the System Safeties topic.
L O W A M B I E N T T E M P
C U T O U T = 2 5 . 0 ° F
The LOW AMBIENT TEMP CUTOUT allows the
user to select the chiller outside ambient temperature
cutout point. If the ambient falls below this point, the
chiller will shut down. Restart can occur when tem-
perature rises 2 °F (1.11 °C) above the cutout setpoint.
This does not apply to a YCRL chiller.
L E A V I N G L I Q U I D T E M P
C U T O U T = 3 6 . 0 ° F
The LEAVING LIQUID TEMP CUTOUT protects the
chiller from an evaporator freeze-up. Anytime the leav-
ing chilled liquid temperature drops to the cutout point,
the chiller shuts down. Restart will be permitted when
the leaving chilled liquid temperature rises 2 °F (1.11
°C) above the cutout setpoint.
When water cooling mode is programmed (OPTIONS
key), the value is fixed at 36.0 °F (2.22 °C) and cannot
be changed. Glycol cooling mode can be programmed
A N T I R E C Y C L E T I M E R
= 6 0 0 S E
C
The programmable anti-recycle timer assures that sys-
tems do not short cycle, and the compressor motors have
sufficient time to dissipate heat after a start. This timer
is programmable under the PROGRAM key between
300 and 600 seconds. Whenever possible, to reduce cy-
cling and motor heating, the anti-recycle timer should
be adjusted as high as possible. The programmable anti-
recycle timer starts the timer when the first compressor
in a system starts. The timer begins to count down. If all
the compressors in the circuit cycle off, a compressor
within the circuit will not be permitted to start until the
anti-recycle timer has timed out. If the lead system has
run for less than 5 minutes, three times in a row, the anti-
recycle timer will be extended to 10 minutes, if currently
programmed for less than 10 minutes.
F A N C O N T R O L O N
P R E S S U R E = X X X P S I G
Does not apply to YCRL.
F A N D I F F E R E N T I A L O F F
P R E S S U R E = X X X P S I G
Does not apply to YCRL.
