AAON LC-054 - Manual (Page 13)

13
Never cut off the main power supply to the
unit, except for complete shutdown. When
power is cut off from the unit, any
compressors using crankcase heaters cannot
prevent refrigerant migration. This means
the compressor will cool down, and liquid
refrigerant may accumulate in the
compressor. Since the compressor is
designed to pump refrigerant gas, damage
may occur when power is restored.
Before unit operation, the main power
switch must be turned on for at least twenty
four hours for units with compressor
crankcase heaters. This will give the
crankcase heater time to clear any liquid
accumulation out of the compressor before it
is required to run.
Always control the system from the control
panel, never at the main power supply
(except for emergency or for complete
shutdown of the system).
The standard compressors must be on a
minimum of 4 minutes and off for a
minimum of 5 minutes. The cycle rate must
be no more than 6 starts per hour.
The variable capacity compressors must be
on a minimum of 3 minutes and off for a
minimum of 3 minutes. The cycle rate must
be no more than 10 starts per hour.
The chiller is furnished with a pressure
differential switch that is factory installed
between the chilled water supply and return
connections. This sensor must not be
bypassed since it provides a signal to the
unit controller that water flow is present in
the heat exchanger and the unit can operate
without the danger of freezing the liquid.
The compressor life will be seriously
shortened by reduced lubrication, and the
pumping of excessive amounts of liquid oil
and refrigerant.
Wiring Diagrams
A complete set of unit specific wiring
diagram in point-to-point form is laminated
in plastic and located inside the control
compartment door.
General Maintenance
When the initial startup is made and on a
periodic schedule during operation, it is
necessary to perform routine service checks
on the performance of the chiller. This
includes reading and recording suction
pressures and checking for normal sub-
cooling and superheat.
Scroll compressors are directional
and will be damaged by operation in
the wrong direction. Low pressure
switches on compressors have been
disconnected after factory testing.
Rotation should be checked by a
qualified service technician at startup
using suction and discharge pressure
gauges and any wiring alteration
should only be made at the unit
power connection.
CAUTION
Rotation must be checked on all
MOTORS AND COMPRESSORS of
three phase units. All motors, to
include and not be limited to pump
motors and condenser fan motors,
should all be checked by a qualified
service technician at startup and any
wiring alteration should only be made
at the unit power connection.
CAUTION