Adjusting Refrigerant Charge; Checking Liquid Sub-Cooling; Checking Evaporator Superheat - AAON RN Series Installation Operation & Maintenance

previous locations. Tighten bolts in a cross
pattern to 6.7 ft-lbs. of torque.
Step 6: Install the fan in the unit.
After placing the fan on the shaft, place the
key in the shaft, make sure the screw on the
bushing is aligned over the key and then
tighten the screw to 9 ft-lbs torque.
CAUTION
Before completing startup and leaving
the unit a complete operating cycle
must be observed to verify that all
components are functioning properly.

Adjusting Refrigerant Charge

Adjusting the charge of a system in the field
must be based on determination of liquid sub-
cooling and evaporator superheat. On a
system with an expansion valve liquid sub-
cooling is more representative of the charge
than evaporator
measurements must be taken.
CAUTION
The Clean Air Act of 1990 bans the
intentional venting
(CFC's and HCFC's) as of July 1,
1992. Approved methods of recovery,
recycling or reclaiming must be
followed. Fines and/or incarceration
may be levied for non-compliance.
Before Charging
Unit being charged must be at or near full
load conditions before adjusting the charge.
Units equipped with hot gas reheat must be
charged with the hot gas reheat valves closed
while the unit is in cooling mode to get the
proper charge. After charging, operate the
unit in reheat (dehumidification) mode to
check for correct operation.
superheat but both
of refrigerant
Units equipped with heat pump options must
be charged in heating mode to get the proper
charge. After charging, operate the unit in
cooling mode to check for correct charge.
Charge may need to be adjusted for cooling
mode. If adjustments are made in the cooling
mode heating mode must be rerun to verify
proper operation.
After adding or removing charge the system
must be allowed to stabilize, typically 10-15
minutes, before
adjustments.
The type of unit and options determine the
ranges for liquid sub-cooling and evaporator
superheat. Refer to the table below when
determining the proper sub-cooling.

Checking Liquid Sub-Cooling

Measure the temperature of the liquid line as
it leaves the condenser coil.
Read the gauge pressure at the liquid line
close to the point where the temperature was
taken. You must use liquid line pressure as it
will vary from discharge pressure due to
condenser coil pressure drop.
Convert the pressure obtained to a saturated
temperature using the appropriate refrigerant
temperature-pressure chart.
Subtract the measured liquid line temperature
from the saturated temperature to determine
the liquid sub-cooling.
Compare calculated sub-cooling to the tables
below for the appropriate coil and system
type and options.

Checking Evaporator Superheat

Measure the temperature of the suction line
close to the compressor.
Read gauge pressure at the suction line close
to the compressor.
making any other
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