AAON F1-060, Installation, Operation & Maintenance Manual, Page: 13 / 56

13
Direct Expansion (DX) Systems
All DX systems include evaporator coils and
thermal expansion valves (TXV).
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
condensing unit 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
shortened by reduced lubrication and the
pumping of excessive amounts of liquid oil
and refrigerant.
Note: Low Ambient Operation
Air-cooled DX units without a low ambient
option, such as condenser fan cycling or the
flooded condenser 0°F low ambient option,
will not operate in the cooling mode of
operation properly when the outdoor
temperature is below 55°F. Low ambient
and/or
economizer options are
recommended if cooling operation below
55°F is expected.
Wiring Diagrams
Unit specific wiring diagrams are laminated
and affixed inside the controls compartment
door.
Condensate Drain Pans
Units require field installed 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.
CRANKCASE HEATER
OPERATION
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