JOHNSON CONTROLS
145
SECTION 7 – UNIT CONTROLS
FORM 150.72-ICOM6
ISSUE DATE: 08/03/2022
7
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 = 3 9 5 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 bar) 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 topic of SYSTEM
SAFETIES.
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 temperature
rises 2°F (1.11°C) above the cutout setpoint.
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
leaving 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 ensures that
systems do not short cycle, and the compressor mo-
tors have sufficient time to dissipate heat after a start.
This timer is programmable under the PROGRAM key
between 300 seconds and 600 seconds. Whenever pos-
sible, to reduce cycling and motor heating, the anti-re-
cycle 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 be-
gins 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,
3 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
The Fan Control On Pressure is the programmed pres-
sure value that is used to stage the condenser fans on, in
relation to discharge pressure. See
in
and
