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IM 830-6
Determining System Superheat
After the subcooling has been determined, check system
superheat.
1. Determine required superheat from superheat range,
2. Measure suction line temperature 6 inches from service
valve.
3. Measure suction line pressure at service valve and
determine saturated suction temperature from
4. Subtract saturated suction temperature from measured
temperature to obtain superheat.
5. Refer to
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 37: Saturated Temperature - Pressure Chart
(ºF)
R410A-PSIG
(ºF)
R410A-PSIG
(ºF)
R410A-PSIG
32
101.1
44
127.7
80
235.8
33
103.2
45
130.2
85
254.7
34
105.2
46
132.6
90
274.5
35
107.4
47
135.1
95
295.5
36
109.5
48
137.5
100
317.6
37
111.7
49
140.1
105
340.9
38
113.9
50
142.6
110
365.4
39
116.2
55
147.0
115
391.2
40
118.4
60
170.1
120
418.3
41
120.7
65
185.2
125
446.9
42
123.0
70
201.1
130
476.8
43
125.4
75
218.0
140
541.4
Table 38: Superheat Range
Outdoor Ambient
Indoor Coil Air Inlet Temp. DB/WB (50% RH)
75/63
80/67
85/71
105
*
*
8-10
100
*
3-5
9-11
95
*
5-7
11-13
90
*
9-11
13-15
85
5-7
10-12
15-17
80
8-10
12-14
18-20
75
10-12
15-17
21-23
70
13-15
19-21
24-26
65
15-17
21-23
26-28
Typical conditions - 95
°
F ambient, 75 psig suction, 285 psig
head pressure, 6 - 7
°
superheat, 15
°
F subcooling
NOTICE
Superheat Adjustment
1. Remove the seal cap from thermal expansion valve
(
).
2. Turn the adjustment screw clockwise to increase
superheat and counterclockwise to decrease superheat
(see
). One complete 360° turn changes
the superheat approximately 3-4°F, 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 79: Superheat Adjustment of TXV
Counterclockwise
To Decrease
Superheat
Clockwise To
Increase Superheat
Remove Seal Cap
Adjustment Nut
Thermal Expansion Valve (TXV)
