JOHNSON CONTROLS
121
SECTION 4 - VSD OPERATION
FORM 160.84-OM1
ISSUE DATE: 9/21/2017
4
OPTISPEED COMPRESSOR DRIVE AND
CHILLER OPERATION (0490A, 0612A, 0730A
AND 1278A AMP MODELS)
When the chiller enters a start command, the OSCD
is commanded to pre-charge, the pre-charge contactor
will close and slowly charge the DC Bus capacitors
through the pre-charge resistors. This is called the
pre-charge period, which will last for 12-seconds. Af-
ter the 12-second time period has expired, the supply
contactor will close and the pre-charge contactor will
open. The supply and pre-charge contactors will re-
main in this state for the duration of the run cycle. The
OSCD logic board provides the commands for the sup-
ply and pre-charge contactors.
All models of HYP drives will control the motor in the
same manner for a normal stop command.
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