AAON SB-018 - Manual (Page 17)

17
All DX systems include evaporator coils,
liquid line filter dryers, thermal expansion
valves (TXV), and scroll compressors.
Compressors are equipped with a positive
pressure forced lubrication system.
Never turn off the main power supply to the
unit, except for servicing, emergency, or
complete shutdown of the unit. When power
is cut off from the unit crankcase heaters
cannot prevent refrigerant migration into the
compressors. This means the compressor
may cool down and liquid refrigerant may
accumulate in the compressor. The
compressor is designed to pump refrigerant
gas and damage may occur when power is
restored.
If power to the unit must be off for more
than an hour, turn the thermostat system
switch to "OFF", or turn the unit off at the
control panel, and leave the unit off until the
main power switch has been turned on again
for at least 24 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 started.
Always control the unit from the thermostat,
or control panel, never at the main power
supply, except for emergency or complete
shutdown of the unit.
During the cooling season, if the air flow is
reduced due to dirty air filters or any other
reason, the cooling coils can get too cold
which will cause excessive liquid to return
to the compressor. As the liquid
concentration builds up, oil is washed out of
the compressor, leaving it starved for
lubrication.
The compressor life will be seriously
shorted by reduced lubrication and the
pumping of excessive amounts of liquid oil
and refrigerant.
Wiring Diagrams
Unit specific wiring diagrams are laminated
and affixed inside the controls compartment
door.
Condensate Drain Pans
Units require drain p-traps and lines to be
connected to the condensate drain pans of
the unit. The lines should be the same pipe
size or larger than the drain connection,
include a p-trap, and pitch downward toward
drain. An air break should be used with long
runs of condensate lines.
Waterside economizer coil units include a
separate condensate drain pan which drains
into the evaporator coil drain pan.
CRANKCASE HEATER
Some units are equipped with
compressor crankcase heaters,
which should be energized at least
24 hours prior to cooling operation, to
clear any liquid refrigerant from the
compressors.
CAUTION
Unit should not be operated without a
p-trap. Failure to install a p-trap may
result in overflow of condensate
water.
CAUTION