Residential Air Conditioners and Heat Pumps Using R-22 and Puron® Refrigerant: Application Guideline and Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
40
Example 2
Jason is servicing a 5-ton R-22 air conditioner with 7/8” suction line. As
part of his basic inspection he believes he has normal airflow because the
air filters are clean, ductwork appears to be properly sized and in good
shape and the evaporator coil is clean. He then checks the superheat and
subcooling at the outdoor unit service valves. Taking pressures and
temperatures he finds the following:
• Liquid line pressure = 260 psig
• Liquid line temperature = 110
F
• Suction line pressure = 60 psig
• Suction line temperature = 65
F
Using an R-22 PT relationship, Jason calculates the subcooling to be
approximately 10
F with 30
F superheat. Because the subcooling is
correct but the superheat appears to be high, he is concerned and decides
to perform the Pseudo Evaporator Superheat check.
Examining the lineset, Jason finds approximately 145 ft of suction line
with 4 long radius elbows. Per
, each fitting has an
equivalent length of 1.4 ft. The total equivalent length of the suction line
is (145’ + (4 * 1.4’)
, Jason determines there
should be 10-psig pressure-drop in the suction line.
Jason now takes the suction line temperature at the outlet of the
evaporator and obtains 51
F. Per the instructions, Jason adds the 10-psig
pressure-drop to the 60-psig pressure at the outdoor unit to get 70-psig at
the evaporator. Saturated pressure of 70-psig equates to approximately
41
F. Jason determines the Evaporator superheat to be (51
F - 41
F =)
10
F. Jason concludes the TXV is functioning properly.
A210716
Fig. 38 – Pseudo Evaporator Superheat Pressure and Temperature Measurement Locations
Table 7 – R-22 System Suction Pressure Drop
Nominal
Size
(Btuh)
Line
OD
(in.)
Pressure
Drop
(psi/100 ft)
Suction
Velocity
Fpm
R-22 Suction Line Pressure Drop (psig)
Total Equivalent Line Length (ft)
20
80
50
100
125
150
175
200
225
250
18000
5/8
13.6
2563
3
7
11
14
17
20
24
27
31
34
5/8
4.0
1539
1
2
3
4
5
6
7
8
9
10
3/4
1.5
1025
0
1
1
1
2
2
3
3
3
4
7/8
0.8
769
0
0
1
1
1
1
1
2
2
2
24000
5/8
6.7
2052
1
3
5
7
8
10
12
13
15
17
3/4
2.5
1367
1
1
2
3
3
4
4
5
6
6
7/8
1.3
1026
0
1
1
1
2
2
2
3
3
3
30000
5/8
10.1
2565
2
5
8
10
13
15
18
20
23
25
3/4
3.8
1708
1
2
3
4
5
6
7
8
9
9
7/8
1.9
1282
0
1
2
2
2
3
3
4
4
5
36000
3/4
5.3
2050
1
3
4
5
7
8
9
11
12
13
7/8
2.6
1538
1
1
2
3
3
4
5
5
6
7
1 1/8
0.7
902
0
0
1
1
1
1
1
1
2
2
42000
3/4
7.0
2392
1
3
6
7
9
10
12
14
16
17
7/8
3.5
1795
1
2
3
3
4
5
6
7
8
9
1 1/8
1.0
1053
0
0
1
1
1
1
2
2
2
2
48000
3/4
8.9
2733
2
4
7
9
11
13
16
18
20
22
7/8
4.4
2051
1
2
4
4
6
7
8
9
10
11
1 1/8
1.2
1203
0
1
1
1
2
2
2
2
3
3
60000
7/8
6.7
2564
1
3
5
7
8
10
12
13
15
17
1 1/8
1.8
1504
0
1
1
2
2
3
3
4
4
5
1 3/8
0.7
987
0
0
1
1
1
1
1
1
2
2
= Line set application not recommended
