Lennox 12HPB Series Installation Instructions Manual page 15

Charging Using Normal Operating Pressures
and the Approach Method
Outdoor Temp. > 65_F (18_C)
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.
12HPB24
Outdoor Coil Outdoor Coil
Air Entering
liq.
Temp.
+10
_F (_C)
PSIG
65 (183.) 144
75 (23.9) 170
85 (29.4) 199
95 (35) 228
105 (40.6) 261
NOTE − Typical pressures only. Indoor evaporator match up, indoor air quantity, and evaporator load will cause the pressures to vary.
Normal Operating Pressures
12HPB30
vap. liq. vap.
+5 +10 +5
PSIG PSIG PSIG
78 140 76
79 164 77
80 194 78
81 224 79
82 259 80
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.
Model
12HPB24
12HPB30
12HPB36
12HPB42
12HPB48
12HPB60
NOTE − For best results, the same thermometer should be used to check
both outdoor ambient and liquid temperatures.
Table 7
12HPB36 12HPB42
liq. vap. liq.
+10 +5 +10
PSIG PSIG PSIG
152 74 152
178 76 179
208 77 210
238 78 241
275 81 278
Page 15
Approach Method
Table 6
Approach Values
Liquid Temp. Minus Ambient Temp.
_F (_C)
6 (3.3)
11 (6.1)
12 (6.7)
10 (5.6)
9 (5)
8 (4.4)
12HPB48
vap. liq. vap.
+5 +10 +5
PSIG PSIG PSIG
75 146 75
76 171 77
77 198 78
78 229 79
79 268 81
12HPB60
liq. vap.
+10 +5
PSIG PSIG
146 73
175 74
206 75
237 76
275 77