Checking superheat and subcooling
R-410A temperature charts list the associated saturation temperature in one column and the
associated pressure in another column. See Table 25 on page 40.
Subcooling
When the refrigerant charge is correct, there is no vapor in the liquid sight glass with the system
operating under full load conditions.
The subcooling temperature of each system can be calculated:
1. Record the temperature of the liquid line at the outlet of the condenser.
2. Subtract it from the saturation temperature listed in Table 27 for the corresponding discharge
pressure.
3. If the rooftop unit lacks an access port for liquid access, subtract the condenser coil pressure
drop value from Table 25 from the discharge pressure to determine the equivalent saturation
temperature.
For example, when the discharge pressure is 388 psig and the liquid line temperature is 95.0°F:
•
Liquid Pressure = Discharge Pressure (388 psig) minus 33 psig = 355 psig
•
Saturation Temperature for 355 psig = 108.0°F
•
Liquid Line Subcooling = Saturation Temperature (108.0°F) minus Liquid Line Temperature
(95.0°) = 13.0°F
Subcooling should be 10.0–14.0°F at design conditions.
Table 27: R-410A pressure and temperature chart
PSIG
Temp °F
PSIG
Temp °F
0
-60
78
20
2
-58
80
21
4
-54
85
24
6
-50
90
26
8
-46
95
29
10
-42
100
32
12
-39
105
34
14
-36
110
36
16
-33
115
39
18
-30
120
41
20
-28
125
43
22
-26
130
45
24
-24
135
47
26
-20
140
49
28
-18
145
51
30
-16
150
53
32
-14
160
57
34
-12
170
60
36
-10
180
64
43
Model DSH024C–120C Horizontal R-410A Air Conditioning Units C-Generation Smart Equipment Controller
Johnson Controls
