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 percent 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
thermistor-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.
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.
Step 12—Final Checks
IMPORTANT: Before leaving job, be sure to do the following:
1. Securely fasten all panels and covers.
2. Tighten service valve-stem caps to 1/12-turn past finger-tight.
3. Leave User’s Manual with owner. Explain system operation
and periodic maintenance requirements outlined in manual.
4. 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.
Table 5—Superheat Charging
OUTDOOR
TEMP
(°F)
EVAPORATOR ENTERING AIR TEMPERATURE (°F WB)
50 52 54 56 58 60 62 64 66 68 70 72 74 76
55 9 12141720232629323537404245
60 7 10121518212427303335384043
65 — 6 101316192124273033363841
70 —— 7 1013161921242730333639
75 ——— 6 9 12 15 18 21 24 28 31 34 37
80 ———— 5 8 12 15 18 21 25 28 31 35
85 —————— 8 11151922263033
90 —————— 5 9 13 16 20 24 27 31
95 ——————— 6 101418222529
100 ———————— 8 1215202327
105 ———————— 5 9 13 17 22 26
110 ————————— 6 11152025
115 —————————— 8 141823
Where a dash (–) appears, do not attempt to charge system under these conditions, or refrigerant slugging may occur. Charge must be weighed in.
NOTE: Superheat °F is at low-side service port.
6
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