AAON RN Series - Adjusting Sub-Cooling and Superheat Temperatures; Freeze Stat Startup; Table 17 - Acceptable Microchannel Air-Cooled Condenser Coil Liquid Sub-Cooling Values

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Table 17 - Acceptable Microchannel Air-Cooled Condenser Coil Liquid Sub-
Cooling Values
Cooling Mode Liquid Sub-Cooling Values(°F)
Ambient
(°F)
Evaporator Coil Saturation Temperature (°F)
40
45
48
50
55
67
9 - 14
8 - 13
8 - 13
7 - 12
5 - 10
72
10 - 15
9 - 14
9 - 14
8 - 13
7 - 12
82
10 - 15
10 - 15
10 - 15
9 - 14
7 - 12
95
10 - 15
10 - 15
10 - 15
9 - 14
8 - 13
105
11 - 16
11 - 16
10 - 15
10 - 15
8 - 13
115
10 - 15
11 - 16
11 - 16
11 - 16
9 - 14
Notes:
1. Microchannel condenser coils are more sensitive to charge. The system must
be running in cooling mode with compressor, supply airflow & condenser fan
speed at full load. The sub-cooling value changes depending on the ambient
temperature reading and the microchannel evaporator coil saturation
temperature. To find the correct sub-cooling value, find the ambient
temperature on the first column and follow that across to the SST (40-55°F).
2. Superheat for Microchannel condenser coils must be between 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 expansion valve may need
adjustment to correct the superheat.
Freeze Stat Startup
Freeze Stat is an adjustable temperature
sensor (-10 to 70°F) mounted on the tubing
of the first cooling circuit and wired to de-
energize all cooling circuits if tubing
temperature falls below setpoint. Option is
used to prevent freezing of evaporator coil.
Recommended Setting: 32° F to 35º F
DO NOT OVERCHARGE!
Refrigerant overcharging leads to
excess refrigerant in the condenser
coils resulting in elevated compressor
discharge pressure.
CAUTION