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Determining System Superheat
After the subcooling has been determined, check system superheat.
1.
Determine required superheat from superheat range, table 23.
2.
Measure suction line temperature 6 inches from service valve.
3.
Measure suction line pressure at service valve and determine
saturated suction temperature from table 22.
4.
Subtract saturated suction temperature from measured temperature
to obtain superheat.
5.
Refer to table 23 and adjust charge as required for correct superheat
at ambient conditions.
NOTICE
Each time that charge is added or removed from the system,
allow the system to run approximately 20 - 30 minutes before
pressure and temperature readings are taken and superheat
calculations made.
NOTICE
If system hunting occurs or subcooling is reduced, it may be
necessary to adjust TXV to obtain correct superheat.
Table 22 —Saturated Temperature - Pressure Chart
(ºF)
R410A-PSIG
(ºF)
32
101.1
44
33
103.2
45
34
105.2
46
35
107.4
47
36
109.5
48
37
111.7
49
38
113.9
50
39
116.2
55
40
118.4
60
41
120.7
65
42
123.0
70
43
125.4
75
Table 23 —Superheat Range
Indoor Coil Air Inlet Temp.
Outdoor
DB/WB (50% RH)
Ambient
75/63
80/67
105
*
*
100
*
3-5
95
*
5-7
90
*
9-11
85
5-7
10-12
80
8-10
12-14
75
10-12
15-17
70
13-15
19-21
65
15-17
21-23
NOTICE
Typical conditions - 95ºF ambient, 75 psig suction, 285 psig
head pressure, 6 - 7º superheat, 15ºF subcooling
Page 32 of 60
R410A-PSIG
(ºF)
R410A-PSIG
127.7
80
235.8
130.2
85
254.7
132.6
90
274.5
135.1
95
295.5
137.5
100
317.6
140.1
105
340.9
142.6
110
365.4
147.0
115
391.2
170.1
120
418.3
185.2
125
446.9
201.1
130
476.8
218.0
140
541.4
85/71
8-10
9-11
11-13
13-15
15-17
18-20
21-23
24-26
26-28
Superheat Adjustment
Remove the seal cap from thermal expansion valve (see figure 91).
1.
2.
Turn the adjustment screw clockwise to increase superheat and
counterclockwise to decrease superheat (see figure 91). One
complete 360º turn changes the superheat approximately 3-4ºF,
regardless of the refrigerant type. As much as 30 minutes may be
required for the system to stabilize after the adjustment is made.
3.
Replace and hand-tighten seal cap.
CAUTION
Do not force adjustment stem of TXV. When adjusting superheat
setting, there are a maximum of 10 turns on the stem. Turning
adjustment stem after reaching stop will damage valve.
Figure 91 - Superheat Adjustment of TXV
Remove Seal Cap
Counterclockwise To
Decrease Superheat
Superheat
Adjustment Screw
Clockwise To Increase
Superheat
IM 817-4
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