JOHNSON CONTROLS
122
FORM 145.05-NOM7
ISSUE DATE: 10/31/2019
SECTION 5 – SEQUENCE OF OPERATION
The following parameters must be programmed into
the Unit Controller through the User Interface:
• OPTIONS key, CONDENSER subsection:
• “COND VALVES INSTALLED” should be
set to COND W/ BYPASS
• “CONDENSER TYPE” should be set to WA-
TER COOLED
• PROGRAM key, CONDENSER subsection:
• “COND WATER CONTROL” should be set
to ENABLED
• “COND WATER SYSTEM” can be set to
either VARIABLE FLOW or CONSTANT
FLOW depending on the building system
• FLUSH CYCLE can be set to either EN-
ABLE or DISABLE depending on the build-
ing system
• SETPOINTS key, CONDENSER subsection:
•
“COND VALVE MIN POS” (default is 30%)
•
“COND BYPASS MAX POS” (default is 50%)
• “DISCHARGE PRESSURE SP MIN”
(default is 225 PSIG)
• “DISCHARGE PRESSURE SP MAX”
(default is 400 PSIG)
Sequence of Operation
The condenser actuator driven valve is inverse acting.
When the voltage output to the valve is 10VDC, the
valve is closed. When the voltage output to the valve is
2VDC or less, the valve is wide open. The CONDENS-
ER WATER VALVE analog output is located at J15-8.
The bypass actuator driven valve is direct acting. When
the voltage output to the valve is 2VDC or less, the
valve is closed. When the voltage output to the valve is
10VDC, the valve is wide open. The BYPASS WATER
VALVE analog output is located at J15-14.
Analog Output to the Valve
No Cooling Needed:
The COND WATER VALVE
analog output is 10VDC (0%), the BYPASS WATER
VALVE is set at the “COND BYPASS MAX POS”
using the SETPOINT key, CONDENSER subsection
when the unit is NOT cooling, the unit's display shows
OCCUPIED or UNOCCUPIED STANDBY, and there
are no compressors running.
• “CURRENT OPER MODE” is UNOCCUPIED
or OCCUPIED COOLING STANDBY (default
is 50%)
Cooling Becomes Active:
The COND WATER VALVE analog output is 2VDC
(100%) and the BYPASS WATER VALVE at 2 VDC
(0%) when a call for cooling using the compressors be
-
comes active.
The COND WATER VALVE analog output is 10VDC
(0%) when the unit is NOT COOLING OCCUPIED
or UNOCCUPIED STANDBY, and the valve is closed
when there are no compressors running.
The COND WATER VALVE analog output is con-
trolled by the CONDENSER PRESSURE PI OUTPUT
when:
• “CURRENT OPER MODE” is UNOCCUPIED or
OCCUPIED COOLING and one of the compressors
is ON. The BYPASS WATER VALVE analog out-
100%
(10 VDC)
0%
(2 VDC)
COND BYPASS
MAX POS
BYPASS VALVE
POSITION
(ECONOMIZER
VALVE AO)
COND WATER
VALVE POSITION
100%
(2 VDC)
0%
(10 VDC)
COND VALVE
MIN POS
LD21634
FIGURE 76 -
BYPASS VALVE POSITION VS. COND
WATER VALVE POSITION
The CONDENSER PRESSURE PI OUTPUT is based
on the lowest of the “AVG PRESS – DISCHARGE
A” when active for 60 seconds, “COMP SYSTEM B
DISCHARGE PRESSURE” when active for 60 sec-
onds, and any additional compressor discharge pres-
sures when active for 60 seconds. The Unit Controller
tries to maintain the pressure to the programmed “DIS-
CHARGE PRESSURE SETPOINT.”
Some of the compressors in these units employ internal
line break protection. The Unit Controller could think
that a compressor is active when it is physically offline.
This causes the Unit Controller to calculate a DIS-
CHARGE PRESSURE MINIMUM demand based on
a compressor that is not operating, which could result
in a discharge high pressure fault. To prevent nuisance
discharge high pressure faults, the Unit Controller also
compares the maximum discharge pressure of the ac-
tive compressor systems to the programmed "DIS-
CHARGE PRESSURE SP MAX." The default value is