Lennox HSXA12-018 Installation Instructions Manual page 17

Approach Method and
Normal Operating Pressures
TXV Systems – 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 8, 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 you used to check
the outdoor ambient temperature to check the liquid
line temperature.
5 − The difference between the ambient and liquid temper-
atures should match values given in table 7. If the val-
ues don't agree with the those in table 7, add refriger-
ant to lower the approach temperature, or recover re-
Normal Operating Pressures In psig (liquid +/− 10 and vapor +/− 5 PSIG)*
Out. Coil
Entering Air
Mode Mode
Temp Temp.
°F (°C)
LIQ
65 (18.3) 238
75 (23.9) 275
fixed
85 (29.4) 317
orifice ifi
95 (35.0) 362
105 (40.6) 410
65 (18.3) 234
75 (23.9) 270
TXV
85 (29.4) 312
95 (35.0) 361
105 (40.6) 409
*These are typical pressures only. Indoor indoor match up, indoor air quality, and indoor load will cause the pressures
to vary.
−018 −024
SUC LIQ SUC LIQ
123 261 131 261
131 300 135 300
136 343 139 343
141 391 143 387
144 441 147 434
133 256 134 256
135 298 137 296
137 344 140 339
138 394 142 384
141 448 143 432
frigerant from the system to increase the approach
temperature.
Be aware of the R410A refrigerant cylinder. It will be
rose−colored. Refrigerant should be added through the
vapor valve in the liquid state. Some R410A cylinders
are equipped with a dip tube which allows you to
draw liquid refrigerant from the bottom of the cylin-
der without turning the cylinder upside−down. The
cylinder will be marked if it is equipped with a dip
tube.
HSXA12 Approach Values
Model No.
−018
−024
−030
−036
−042
−048
−060
Use table 8 to perform maintenance checks. Table 8
is not a procedure for charging the system. Minor
variations in these pressures may be due to differ-
ences in installations. Significant deviations could
mean that the system is not properly charged or that
a problem exists with some component in the system.
Table 8
−030 −036
SUC LIQ SUC LIQ
128 268 130 254
133 308 134 296
138 351 138 340
141 398 142 389
145 447 146 440
137 264 135 256
139 305 138 296
141 349 139 341
144 396 140 389
146 446 143 440
Page 17
Table 7
Approach Temperature
Liquid Line −
Outdoor Ambient °F (°C)
10 (5.6)
12 (6.7)
13 (7.2)
12 (6.7)
11 (6.1)
13 (7.2)
14 (7.8)
IMPORTANT
−042 −048
SUC LIQ SUC
121 270 124
128 311 130
133 356 134
138 404 139
142 456 143
124 269 131
127 312 133
133 357 135
136 406 137
140 460 140
−060
LIQ SUC
280 121
332 126
379 130
427 135
479 140
262 121
304 127
349 132
397 136
449 140