Page 15
Charging Using Normal Operating Pressures
and the Approach Method
Outdoor Temp. >
65F (18C)
The following procedure is intended as a general guide and
is for use on expansion valve systems only. For best results,
indoor temperature should be 70°F (21°C) to 80°F (26°C).
Monitor system pressures while charging.
1 − Record outdoor ambient temperature using a digital
thermometer.
2 − Attach high pressure gauge set and operate unit for
several minutes to allow system pressures to stabilize.
3 − Compare stabilized pressures with those provided in
table 7, Normal Operating Pressures." Minor varia-
tions in these pressures may be expected due to differ-
ences in installations. Significant differences could
mean that the system is not properly charged or that a
problem exists with some component in the system.
Pressures higher than those listed indicate that the
system is overcharged. Pressures lower than those
listed indicate that the system is undercharged. Verify
adjusted charge using the approach method.
Approach Method
4 − Use the same digital thermometer used to check out-
door ambient temperature to check liquid line tempera-
ture. Verify the unit charge using the approach method.
5 − The difference between the ambient and liquid temper-
atures should match values given in table 6. If the val-
ues don’t agree with the those in table 6, add refriger-
ant to lower the approach temperature or recover re-
frigerant from the system to increase the approach
temperature.
Table 6
Approach Values
Model
Liquid Temp. Minus Ambient Temp.
_F (_C)
12HPB24 6 (3.3)
12HPB30 11 (6.1)
12HPB36 12 (6.7)
12HPB42 10 (5.6)
12HPB48 9 (5)
12HPB60 8 (4.4)
NOTE − For best results, the same thermometer should be used to check
both outdoor ambient and liquid temperatures.
Table 7
Normal Operating Pressures
Outdoor Coil
12HPB24 12HPB30 12HPB36 12HPB42 12HPB48 12HPB60
Air Entering
Temp.
F (C)
liq.
+
10
PSIG
vap.
+
5
PSIG
liq.
+
10
PSIG
vap.
+
5
PSIG
liq.
+
10
PSIG
vap.
+
5
PSIG
liq.
+
10
PSIG
vap.
+
5
PSIG
liq.
+
10
PSIG
vap.
+
5
PSIG
liq.
+
10
PSIG
vap.
+
5
PSIG
65 (183.) 144 78 140 76 152 74 152 75 146 75 146 73
75 (23.9) 170 79 164 77 178 76 179 76 171 77 175 74
85 (29.4) 199 80 194 78 208 77 210 77 198 78 206 75
95 (35) 228 81 224 79 238 78 241 78 229 79 237 76
105 (40.6) 261 82 259 80 275 81 278 79 268 81 275 77
NOTE − Typical pressures only. Indoor evaporator match up, indoor air quantity, and evaporator load will cause the pressures to vary.
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