JOHNSON CONTROLS
120
FORM 145.05-NOM7
ISSUE DATE: 10/31/2019
SECTION 5 – SEQUENCE OF OPERATION
Condenser Valve Only
Under this mode of operation, the unit has an actuator
driven water valve that controls the flow of condenser
water through the water-cooled condenser.
WATER-COOLED
CONDENSER
WATER
SUPPLY
WATER
RETURN
Condenser Valve ONLY
CONDENSER
VALVE
M
LD21631
FIGURE 73 -
CONDENSER AND PIPING DIAGRAM
W/ CONDENSER ONLY VALVE FROM THE FACTORY
COND WATER CONTROL:
This setting indicates
that the controller controls the water flow through the
condenser by modulating the condenser water valve
and condenser bypass valves (if field installed).
COND VALVE MIN POS:
This setpoint is the mini-
mum valve position that the condenser water valve
maintains whenever a compressor is ON.
COND BYPASS MAX POS:
This setpoint is the
maximum valve position that the condenser water by-
pass valve can be opened to during operation.
The following parameters must be programmed into
the Unit Controller through the User Interface:
Default Settings can be used.
• OPTIONS key, CONDENSER subsection:
• “COND VALVES INSTALLED” should be
set to COND ONLY
• “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”
• “DISCHARGE PRESSURE SP MIN”
(default is 225 PSIG)
• “DISCHARGE PRESSURE SP MAX”
(default is 400 PSIG)
If a flow switch is installed, see the following sections.
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.
“DISCHARGE PRESSURE SP MAX” – SETPOINTS
key, CONDENSER subsection.
Analog Output to the Valve
No Cooling Needed:
The COND WATER VALVE
analog output is 10VDC (0%) when the unit is NOT
Cooling and unit's display shows OCCUPIED or UN-
OCCUPIED STANDBY and the valve is closed when
there is no compressors running.
Cooling Becomes Active:
The COND WATER
VALVE analog output is 2VDC (100%) open when
“CURRENT OPER MODE” is UNOCCUPIED or
OCCUPIED COOLING, compressor is ON.
The CONDENSER PRESSURE PI OUTPUT is based
on the lowest of the “AVG PRESS – DISCHARGE A”
when active for 60 seconds, “COMP SYSTEM B DIS-
CHARGE PRESSURE” when active for 60 seconds,
and any additional compressor discharge pressures when
active for 60 seconds. The Unit Controller compares the
minimum pressure of each of the active compressor sys-
tems to the programmed “DISCHARGE PRESSURE
SETPOINT” (default value is 225 PSIG) and generates
DISCHARGE PRESSURE MINIMUM demand.
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