JOHNSON CONTROLS
172
FORM 150.67-NM2
ISSUE DATE: 01/31/2019
SECTION 8 – UNIT OPERATION
FIGURE 55 - 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
Figure 57 on page 173. The pots do not have numeri-
cal 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 poten-
tiometers shown in Figure 57 on page 173. 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 cal-
culate the 0 RPM pressure.
The VFD will ramp up the speed of the fan as pres-
sure rises above the low end of the speed control range.
Throughout the pressure control range, the VFD con-
trols 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 pres-
sure 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-configured at the factory prior to ship-
ping 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 fol-
lowing Table.
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