Carrier AquaForce B Series Controls, Start-Up, Operation, Service And Troubleshooting Instructions page 81

At each drive where the LEN wiring enters, connects, and exits
to the next drive, the LEN shield must be connected together to
form a continuous ground, but not grounded in the drive itself.
At the last VFD of the daisy chain, the LEN shield must be
grounded at the drive. To do this, strip the LEN wire cable to
expose the shield under the jacket and pinch LEN wire cable
within the clamp as shown in Fig. 79.
Additionally, it is recommended that the BUS TER (Bus Ter-
mination) DIP Switch be turned ON at the last VFD in the dai-
sy chain. This switch is located behind the Local Control Panel
(LCP). See Fig. 80.
COMPRESSOR DRIVES
Each unit is equipped with two VFDs to control the compres-
sor operation, one for each circuit. The VFDs vary the operat-
ing speed of the compressors by changing the input power fre-
quency over a programmed range. The compressor VFDs
should not be operated below minimum programmed frequen-
cy, to ensure adequate oil return on the unit. See Fig. 81 for
compressor VFD locations.
For all chillers, the VFDs are inside the control panel. The right
and left doors allow access to the drives and displays.
CONDENSER FAN DRIVES
Chillers with M or H in the 10th position of the model number
or with the Low Ambient option will have condenser fans on
each circuit which are controlled by one or two VFDs. The
fans on each circuit all operate together at the same prepro-
grammed frequency. Table 50 shows the standard tier fan se-
quences. Tables 51-53 show which condenser fans are con-
trolled by each drive. See Tables 51-53 for typical fan VFD ar-
rangement. See Fig. 82 for typical fan VFD location.
Fig. 79 — LEN Shield Grounding
Fig. 80 — BUS TER Location
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