JOHNSON CONTROLS
108
FORM 150.27-NM1
ISSUE DATE: 09/30/2015
SECTION 7 – UNIT CONTROLS
S Y S X S P = 7 2 . 1 P S I G
D P = 2 2 7 . 0 P S I G
These displays show suction and discharge pressures
for each system. The discharge pressure transducer is
optional on some models.
If the optional discharge transducer is not installed, the
discharge pressure would display 0 PSIG (0 barg).
The minimum limits for the display are:
•
Suction Pressure: 0 PSIG (0 barg)
•
Discharge Pressure: 0 PSIG (0 barg)
The maximum limits for the display are:
•
Suction Pressure: 400 PSIG (27.58 barg)
•
Discharge Pressure: 650 PSIG (44.82 barg)
S Y S X H O U R S 1 = X X X X X
2 = X X X X X, 3 = X X X X X
S Y S X S T A R T S 1 = X X X X X
2 = X X X X X, 3 = X X X X X
The above two messages will appear sequentially for
each system. The first display shows accumulated run-
ning hours of each compressor for the specific system.
The second message shows the number of starts for
each compressor on each system.
Run times and starts will only be displayed
for the actual number of systems and
compressors on the unit.
A total of 99,999 hours and starts can be logged before
the counter rolls over to “0”.
This display of the load and unload timers indicate
the time in seconds until the unit can load or unload.
Whether the systems loads or unloads is determined by
how far the actual liquid temperature is from setpoint.
A detailed description of unit loading and unloading is
covered under the topic of Capacity Control.
L O A D T I M E R 5 8 S E C
U N L O A D T I M E R 0 S E C
C O O L I N G D E M A N D
2 O F 8 S T E P S
The display of COOLING DEMAND indicates the
current “step” in the capacity control scheme when in
Return Water Control Mode. The number of available
steps are determined by how many compressors are in
the unit. In the above display, the “2” does not mean
that two compressor are running but only indicates that
the capacity control scheme is on step 2 of 8. Capacity
Control is covered in more detail in this publication
which provides specific information on compressor
staging (for Return Water Control only).
T E M P E R R O R X X X . X ° F
T E M P R A T E X X X . X ° F / M
The COOLING DEMAND message will be replaced
with this message when Leaving Chilled liquid control
is selected. This message indicates the temperature er-
ror and the rate of change of the chilled liquid tempera-
ture.
L E A D S Y S T E M I S
S Y S T E M N U M B E R 2
This display indicates the current LEAD system. In
this example system 2 is the LEAD system, making
system 1 the LAG system. The LEAD system can be
manually selected or automatic.
Refer to the program-
ming under the Options Key on Page 123.
The Lead
System display will only appear on a two system unit.
A unit utilizing Hot Gas Bypass should
be programmed for MANUAL with sys
-
tem 1 as the lead system. Failure to do so
will prevent hot gas operation if system
2 switches to the lead system when pro-
grammed for AUTOMATIC LEAD/LAG.
