JOHNSON CONTROLS
172
FORM 150.67-NM2 (209)
Unit Operation
The VFD will ramp up the speed of the fan as pressure rises
above the low end of the speed control range. Throughout
the pressure control range, the VFD controls the speed
of the fan based on discharge pressure in the range of
approx 260-292 PSIG. At pressures above 260 PSIG,
the VFD will run the system fan at full speed.
As pressure drops below 292 PSIG, the VFD will
slow the speed of the fan to try to maintain discharge
pressure within the control range. The VFD will try
to maintain pressure in the range of 260-292 PSIG by
raising and lowering the speed of the fan. If pressure
drops below 260 PSIG, the VFD will virtually turn the
system fan completely off. Some slight fan movement
or very slow rotation may be noted, although the fan
may appear to stop completely.
CONFIGURATION (JUMPERS AND
POTENTIOMETERS)
Each VFD is pre-con
fi
gured at the factory prior to
shipping and should be ready for operation when
it arrives onsite. A quick check of the settings is
recommended. The jumpers must be in the positions
shown in the following Table.
FIG. 32 –
TYPICAL VFD ENCLOSURE CONFIGURATIONS
Dual System VFD Enclosure
SYS. #2
SYS. #1
Single System VFD Enclosure
LD12081
LD11299a
VFD JUMPERS
J2
REMOVE
—
J3
IN
—
J4
REMOVE
—
J5
IN
—
J6
IN
—
J7
IN
—
J8
IN
—
J9
IN FOR 60 HZ
REMOVE FOR
50 HZ
Potentiometer settings are also preset at the factory.
The potentiometers should be in the positions shown
in Fig.34. The pots do not have numerical settings and
are set according to the arrow positions indicated. DO
NOT change the potentiometer settings unless they do
not match the positioning of the potentiometers shown
in Fig. 34. P1 should be full CW (260 PSIG) and
P2 should be full CCW (32 PSIG).
Modifying these
settings may cause damage to the chiller or control
problems.
The P1 pot sets the setpoint which is the top end of the
control range. This setting is the discharge pressure
at which the fan will be operating at full speed. The
P2 pot sets the range. This is the range of pressure
where the VSD modulates the fan speed from 0 RPM
to full speed. The range is subtracted from the setpoint
to calculate the 0 RPM pressure.
Summary of Contents for YCAL0019
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Page 65: ...FORM 150 67 NM2 209 65 JOHNSON CONTROLS 5 5 CONNECTION WIRING DIAGRAM CON T LD12703B...
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