AAON RN-140 - Manual (Page 27)

27
Never cut 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
will 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 servicing, 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.
Note: Low Ambient Operation
Air-cooled DX units without a low ambient
option, such as condenser fan cycling or the
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.
Note:
Multiple Units with Multiple
Thermostats
When several heating and cooling units are
used to condition a space all unit thermostat
switches must be set in either heating mode,
cooling mode or off. Do not leave part of the
units switched to the opposite mode.
Cooling only units should be switched off at
the thermostat during the heating season.
Gas or Electric Heating
The unit is designed to heat a given amount
of air while operating. If this amount of air
is greatly reduced, approximately 1/3 during
the heating season, the gas heat exchanger or
electric heating coil may overheat, and may
cut the burner or heater off entirely by action
of the safety high temperature limit devices
which are factory mounted at the heat
exchanger and supply fan areas.
Airflow should be adjusted after installation
to obtain an air temperature rise within the
range specified on the unit rating plate at the
required external static pressure.
Polyolester (POE) and Polyvinylether
(PVE) oils are two types of lubricants
used in hydrofluorocarbon (HFC)
refrigeration systems. Refer to the
compressor label for the proper
compressor lubricant type.
CAUTION