AAON RQ-006 - Manual (Page 54)

54
The type of unit and options determine the
ranges for liquid sub-cooling and evaporator
superheat. Refer to Table 13 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 Table 14
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 14 - Acceptable Refrigeration Circuit
Values
Air-Cooled Cond./Air-Source Heat Pump
Sub-Cooling 12-18°F
Sub-Cooling with
Hot Gas Reheat
15-22°F
Superheat 8-15°F
Water-Cooled Cond./Water-Source Heat
Pump
Sub-Cooling 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.
DO NOT OVERCHARGE!
Refrigerant overcharging leads to
excess refrigerant in the condenser
coils resulting in elevated compressor
discharge pressure.
CAUTION
Thermal expansion valve must be
adjusted to approximately 8-15°F of
suction superheat. Failure to have
sufficient superheat will damage the
compressor and void the warranty.
CAUTION