AAON CF Series - Table 3 - Acceptable Fin & Tube Refrigeration Circuit Values

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Table 3 - Acceptable Fin & Tube
Refrigeration Circuit Values
The type of unit and options determine the
ranges for liquid sub-cooling and evaporator
superheat. Refer to Table 3 when determining
the proper sub-cooling.
For units equipped with low ambient
(-17.2°C [0°F]) option see the special
charging instructions at the end of this
section.
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 Table 3
for the appropriate unit type and options.
Notes:
1. Must be charged with the hot gas valve
closed. After charging, operate the unit in
reheat (dehumidification) mode to check for
correct operation.
2. The sub-cooling value in this table is for the
unit running in cooling mode of operation.
After charging, operate the unit in heating
mode to check for correct operation.
3. The sub-cooling value in this table is for the
unit running in cooling mode of operation
and the hot gas valve closed. After charging,
operate the unit in reheat (dehumidification)
mode to check for correct operation and then
in heating mode to check for correct
operation.
4. Sub-cooling must be increased by -17.2°C
(1°F) per 3 meters (10 feet) of vertical liquid
line rise for R-410A (AHU above CU). For
example, a cooling only unit with hot gas
reheat and a vertical liquid drop can charge to
a sub-cooling value of 2.8 - 8.3°C (5-15°F),
but a cooling only unit with hot gas reheat
and a vertical liquid rise of 9.1 m (30 ft) must
charge to a sub-cooling value of at least 4.4 -
8.3°C (8-15°F). DO NOT OVERCHARGE.
Refrigerant overcharging leads to excess
refrigerant in the condenser coils resulting in
elevated compressor discharge pressure.
Cooling
Mode Liquid
Sub-Cooling
Values (°C)
Cooling
Mode Liquid
Sub-Cooling
Values (°F)
Cooling Only Unit
4
4.4 - 8.3
8-15
Cooling Only Unit
with Hot Gas Reheat
1,4
2.8 - 8.3 5-15
Heat PumpUnit
2,4
1.1 - 2.2
2-4
Heat Pump Unit with
Hot Gas Reheat
3,4
1.1 - 3.3 2-6
Cooling Only Unit
with LAC
4
4.4 - 8.3 8-15
Cooling Only Unit
with Hot Gas Reheat
& LAC
4
4.4 - 8.3 8-15