AAON SA-070 - Manual (Page 46)

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will vary from discharge pressure due to
condenser 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 table
below for the appropriate unit 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.
Convert the pressure obtained to a saturated
temperature using the appropriate refrigerant
temperature-pressure chart.
Subtract the saturated temperature from the
measured suction line temperature to
determine the evaporator superheat.
Compare calculated superheat to the table
below for the appropriate unit type and
options.
Table 8 - Acceptable Refrigerant Circuit
Values
Air-Cooled Condenser/
Air-Source Heat Pump
Sub-Cooling 12-18°F
Sub-Cooling with
Hot Gas Reheat
15-22°F
Superheat 8-15°F
Water-Cooled Condenser/
Water-Source Heat Pump
Sub-Cooling 4-8°F
Sub-Cooling with
Hot Gas Reheat
4-8°F
Superheat 8-15°F
Adjusting
Sub-Cooling and Superheat
Temperatures
The system is overcharged if the sub-cooling
temperature is too high and the evaporator is
fully loaded (low loads on the evaporator
result in increased sub-cooling) and the
evaporator
superheat is within the
temperature range as shown in the table
above (high superheat results in increased
sub-cooling).
Correct an overcharged system by reducing
the amount of refrigerant in the system to
lower the sub-cooling.
The system is undercharged if the superheat
is too high and the sub-cooling is too low
Correct an undercharged system by adding
refrigerant to the system to reduce superheat
and raise sub-cooling.
If the sub-cooling is correct and the
superheat is too high, the TXV may need
adjustment to correct the superheat.
DO NOT OVERCHARGE!
Refrigerant overcharging leads to
excess refrigerant in the condenser
coils resulting in elevated compressor
discharge pressure.
CAUTION