SERVICING
44 Rev 1
S-107 UNDERFEEDING
Underfeeding by the expansion valve results in low system
capacity and low suction pressures.
If these symptoms are observed:
1. Check for a restricted liquid line or drier. A restriction will
be indicated by a temperature drop across the drier.
2. Check the operation of the power element of the valve as
described in S-26 Checking Expansion Valve Opera-
tion.
S-108 SUPERHEAT
The expansion valves are factory adjusted to maintain 8 to
12 degrees superheat of the suction gas at the service valve.
Before checking the superheat or replacing the valve, per-
form all the procedures outlined under Air Flow, Refrigerant
Charge, Expansion Valve - Overfeeding, Underfeeding.
These are the most common causes for evaporator mal-
function.
CHECKING SUPERHEAT
Refrigerant gas is considered superheated when its tem-
perature is higher than the saturation temperature corre-
sponding to its pressure. The degree of superheat equals
the degrees of temperature increase above the saturation
temperature at existing pressure. See Temperature - Pres-
sure Chart (next column).
1. Attach an accurate thermometer or preferably a thermo-
couple type temperature tester to the suction line at a
point at least 6" from the compressor.
2. Install a low side pressure gauge on the suction line
service valve at the outdoor unit.
3. Record the gauge pressure and the temperature of the
line.
4. Convert the suction pressure gauge reading to tempera-
ture by finding the gauge reading in Temperature -
Pressure Chart and reading to the left, find the tempera-
ture in the °F column.
5. The difference between the thermometer reading and
pressure to temperature conversion is the amount of
superheat.
EXAMPLE:
a. Suction Pressure = 84
b. Corresponding Temp. °F = 50
c. Thermometer on Suction Line = 63°F
To obtain the degrees temperature of superheat subtract
50.0 from 63.0°F.
The difference is 13° Superheat. The 13° Superheat would
fall in the ± range of allowable superheat.
SUPERHEAT ADJUSTMENT
The expansion valves used on Amana coils are factory set
and are not field adjustable. If the superheat setting be-
comes disturbed, replace the valve.
On systems using capillary tubes or flow control restrictors,
superheat is adjusted in accordance with the "DESIRED
SUPERHEAT vs. OUTDOOR TEMP" chart as explained in
section S-103 CHARGING
Temp.
°F.
Gauge Pressure
(PSIG) Freon-22
Temp.
°F.
Gauge Pressure
(PSIG) Freon-22
-40
-38
-36
-34
0.61
1.42
2.27
3.15
60
62
64
65
102.5
106.3
110.2
114.2
-32
-30
-28
-26
4.07
5.02
6.01
7.03
68
70
72
74
118.3
122.5
126.8
131.2
-24
-22
-20
-18
8.09
9.18
10.31
11.48
76
78
80
82
135.7
140.5
145.0
149.5
-16
-14
-12
-10
12.61
13.94
15.24
16.59
84
86
88
90
154.7
159.8
164.9
170.1
-8
-6
-4
-2
17.99
19.44
20.94
22.49
92
94
96
96
175.4
180.9
186.5
192.1
0
2
4
6
24.09
25.73
27.44
29.21
100
102
104
106
197.9
203.8
209.9
216.0
8
10
12
14
31.04
32.93
34.88
36.89
108
110
112
114
222.3
228.7
235.2
241.9
16
18
20
22
38.96
41.09
43.28
45.53
116
118
120
122
248.7
255.6
262.6
269.7
24
26
28
30
47.85
50.24
52.70
55.23
124
126
128
130
276.9
284.1
291.4
298.8
32
34
36
38
57.83
60.51
63.27
66.11
132
134
136
136
306.3
314.0
321.9
329.9
40
42
44
46
69.02
71.99
75.04
78.18
140
142
144
146
338.0
346.3
355.0
364.3
48
50
52
54
81.40
84.70
88.10
91.5
158
150
152
154
374.1
384.3
392.3
401.3
56
58
95.1
98.8
156
158
160
411.3
421.8
433.3
