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Step 11—Check Charge
UNIT CHARGE
Factory charge is shown on unit rating plate. Adjust charge by
following procedure shown on charging tables located on unit.
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NOTE: If superheat or subcooling charging conditions are not
favorable, charge must be weighed in accordance with unit rating
plate ± 0.6 oz/ft of 3/8-in. liquid line above or below 15 ft
respectively.
EXAMPLE:
To calculate additional charge required for a 25-ft line set:
25 ft - 15 ft = 10 ft X 0.6 oz/ft = 6 oz of additional charge
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COOLING ONLY PROCEDURE
Units with Cooling Mode TXV
Units installed with cooling mode TXV require charging with the
subcooling method.
1. Operate unit a minimum of 10 minutes before checking
charge.
2. Measure liquid service valve pressure by attaching an accurate
gage to service port.
3. Measure liquid line temperature by attaching an accurate
thermistor type or electronic thermometer to liquid line near
outdoor coil.
4. Refer to unit rating plate for required subcooling temperature.
5. Refer to Table 3. Find the point where required subcooling
temperature intersects measured liquid service valve pressure.
6. To obtain required subcooling temperature at a specific liquid
line pressure, add refrigerant if liquid line temperature is
higher than indicated or reclaim refrigerant if temperature is
lower. Allow a tolerance of ± 3°F.
Units with Indoor Pistons
Units installed with indoor pistons require charging with the
superheat method.
The following procedure is valid when indoor airflow is within
± 21% of its rated CFM.
1. Operate unit a minimum of 10 minutes before checking
charge.
2. Measure suction pressure by attaching a gage to suction valve
service port.
3. Measure suction temperature by attaching an accurate ther-
mistor type or electronic thermometer to suction line at service
valve.
4. Measure outdoor air dry-bulb temperature with thermometer.
5. Measure indoor air (entering indoor coil) wet-bulb tempera-
ture with a sling psychrometer.
6. Refer to Table 4. Find outdoor temperature and evaporator
entering air wet-bulb temperature. At this intersection, note
superheat.
7. Refer to Table 5. Find superheat temperature located in item 6
and suction pressure. At this intersection, note suction line
temperature.
8. If unit has a higher suction line temperature than charted
temperature, add refrigerant until charted temperature is
reached.
Table 3—Required Liquid-Line Temperature (°F)
LIQUID
PRESSURE AT
SERVICE VALVE
(PSIG)
134
141
148
156
163
171
179
187
196
205
214
223
233
243
253
264
274
285
297
309
321
331
346
359
9. If unit has a lower suction line temperature than charted
temperature, reclaim refrigerant until charted temperature is
reached.
10. If outdoor air temperature or pressure at suction valve
changes, charge to new suction line temperature indicated on
chart.
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Step 12—Final Checks
IMPORTANT: Before leaving job, be sure to do the following:
1. Check factory tubing on both indoor and outdoor units. Ensure
tubes are not rubbing against each other or any sheet metal.
Pay close attention to feeder tubes, making sure wire ties on
feeder tubes are secure and tight.
2. Securely fasten all panels and covers.
3. Tighten service valve stem caps to 1/12-turn past finger tight.
4. Leave User's Manual with owner. Explain system operation
and periodic maintenance requirements outlined in manual.
5. Fill out Dealer Installation Checklist and place in customer
file.
CARE AND MAINTENANCE
For continuing high performance and to minimize possible equip-
ment failure, periodic maintenance must be performed on this
equipment.
Frequency of maintenance may vary depending upon geographic
areas, such as coastal applications.
5
REQUIRED SUBCOOLING
TEMPERATURE
(°F)
5
10
15
71
66
61
74
69
64
77
72
67
80
75
70
83
78
73
86
81
76
89
84
79
92
87
82
95
90
85
98
93
88
101
96
91
104
99
94
107
102
97
110
105
100
113
108
103
116
111
106
119
114
109
122
117
112
125
120
115
128
123
118
131
126
121
134
129
124
137
132
127
140
135
130
20
56
59
62
65
68
71
74
77
80
83
86
89
92
95
98
101
104
107
110
113
116
119
122
125
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