AAON F1-060, Installation, Operation & Maintenance Manual, Page: 23 / 56

23
Checking Liquid Sub-cooling
1.
Measure the temperature of the liquid
line as it leaves the condenser coil.
2. Read the gauge pressure reading of 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.
3. Convert the pressure obtained in Step 2 to
a saturated temperature using the
appropriate refrigerant temperature-pressure
chart.
4. Subtract the measured liquid line
temperature in Step 1 from the saturated
temperature in Step 3 to determine the liquid
sub-cooling.
5. Compare calculated sub-cooling to
TABLE 7 for the appropriate unit type and
options.
Checking Evaporator Superheat
1.
Measure the temperature of the suction
line close to the compressor.
2. Read gauge pressure at the suction line
close to the compressor.
3. Convert the pressure obtained in Step 2 to
a saturated temperature using the
appropriate refrigerant temperature-pressure
chart.
4. Subtract the saturated temperature in Step
3 from the measured suction line
temperature in Step 1 to determine the
evaporator superheat.
5. Compare calculated superheat to TABLE
7 for the appropriate unit type and options.
Adjusting Sub-cooling and Superheat
Temperatures
The system is overcharged if:
1. the sub-cooling temperature is too high
and
2. the evaporator is fully loaded (low loads
on the evaporator result in increased sub-
cooling)
and
3. the evaporator superheat is within the
temperature range as shown in Table 7 (high
superheat results in increased sub-cooling)
Table 7 - Acceptable Refrigeration Circuit
Values
Air-Cooled Cond./Air-Source Heat Pump
Sub-Cooling** 8-15°F / 2-4°F (HP)*
Sub-Cooling with
Hot Gas Reheat**
8-15°F / 2-6°F (HP)*
Superheat*** 8-15°F
*In cooling mode operation
**Sub-cooling must be increased by 2°F per
20 feet of vertical liquid line rise for R-410A
***Superheat will increase with long
suction line runs.
Correct an overcharged system by reducing
the amount of refrigerant in the system to
lower the sub-cooling.
The system is
undercharged if:
1. The superheat is too high and
2. The sub-cooling is too low.
DO NOT OVERCHARGE!
Refrigerant overcharging leads to
excess refrigerant in the condenser
coils resulting in elevated compressor
discharge pressure.
CAUTION