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.
39
Example 1
While on a service call, after checking for proper indoor and outdoor
airflow, Tom finds the following pressures and temperatures at the
service valves of a Puron air conditioner:
• Liquid line pressure = 340 psig
• Liquid line temperature = 97°F
• Suction line pressure = 125 psig
• Suction line temperature = 70°F
Using a Puron PT chart, the subcooling is determined to be 8°F, which is
within ±3 of the 10°F listed on the rating plate. Tom believes the charge
is correct. He calculates the superheat to be approximately 27°F
superheat. The apparently high superheat has Tom concerned.
Tom uses the Pseudo Evaporator Superheat method to check the TXV
performance. The system is a 3-ton Puron air conditioner with 75 feet
equivalent length of 3/4” suction line. Based on
, the system has
approximately 3-psig pressure drop in the vapor line. Per the
instructions, he takes the suction line temperature at the outlet of the
evaporator and finds it to be 53°F. Tom adds 3 psig to the 125-psig
suction pressure at the outdoor unit to get 128 psig evaporator pressure.
The saturated pressure of 128 equates to 44°F. Tom calculates the
evaporator superheat to be (53°F - 44°F =) 9°F. The TXV appears to be
operating properly.
NOTE:
The additional superheat at the compressor is due principally to
heat gain in the 75 feet of suction line with a minor contribution by the
pressure drop. Because the suction line of the lineset was the same size
as the vapor service valve fitting and less than 80 feet, Tom could have
ignored the pressure drop in the suction line and obtained the evaporator
superheat by using the vapor service valve pressure of 125 psig
(saturated temperature = 43°F) and the evaporator outlet temperature of
53°F. The evaporator superheat is calculated to be (53°F – 43°F =) 10
°F.
Table 6 – Puron System Suction Pressure Drop
Nominal
Size
(Btuh)
Suction Line
OD
(in.)
Pressure
Drop
(psi/100 ft)
Suction
Velocity
fpm
Puron Suction Line Pressure Drop (psig)
Total Equivalent Line Length (ft)
20
80 50
100
125
150
175
200
225
250
18000
1/2
9.9
1649
2
5
8
10
12
15
17
20
25 22
5/8
3.1
1018
1
2
2
3
4
5
5
6
8 7
3/4
1.2
678
0
1
1
1
1
2
2
2
3 3
24000
1/2
16.7
2199
3
8
13
17
21
25
29
33
42 38
5/8
5.2
1357
1
3
4
5
7
8
9
10
13 12
3/4
2.0
904
0
1
2
2
2
3
3
4
5 4
7/8
1.0
678
0
0
1
1
1
1
2
2
2 2
30000
5/8
7.8
1696
2
4
6
8
10
12
14
16
20 18
3/4
2.9
1130
1
1
2
3
4
4
5
6
7 7
7/8
1.5
848
0
1
1
1
2
2
3
3
4 3
36000
5/8
10.9
2036
2
5
9
11
14
16
19
22
27 24
3/4
4.1
1356
1
2
3
4
5
6
7
8
10 9
7/8
2.0
1017
0
1
2
2
3
3
4
4
5 5
42000
5/8
14.1
2375
3
7
11
14
18
21
25
28
35 32
3/4
5.4
1582
1
3
4
5
7
8
9
11
14 12
7/8
2.7
1187
1
1
2
3
3
4
5
5
7 6
1 1/8
0.8
696
0
0
1
1
1
1
1
2
2 2
48000
3/4
6.9
1808
1
3
6
7
9
10
12
14
17 16
7/8
3.5
1357
1
2
3
3
4
5
6
7
9 8
1 1/8
1.0
796
0
0
1
1
1
1
2
2
2 2
60000
3/4
10.4
2260
2
5
8
10
13
16
18
21
26 23
7/8
5.2
1696
1
3
4
5
6
8
9
10
13 12
1 1/8
1.4
995
0
1
1
1
2
2
3
3
4 3
= Line set application not recommended
