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a TXV, the subcooling method must be used. Heat pumps must be
operating in the cooling mode. To charge by superheat, a service
technician needs an accurate superheat thermocouple or
thermistor-type thermometer, a sling psychrometer, and a gage
manifold. Do not use mercury or small-dial-type thermometers as
they are not adequate for this type of measurement. Then use 1 of
the following procedures:
SUPERHEAT CHARGING METHOD
1. Operate a unit a minimum of 10 minutes before checking
charge.
2. Measure vapor pressure by attaching a gage to vapor
valve-service port.
3. Measure vapor-line temperature by attaching a service
thermometer to unit vapor line near vapor valve. On a heat
pump, attach to the suction tube between the accumulator
and the compressor. Insulate thermometer for accurate
readings.
4. Measure outdoor-air, dry-bulb temperature with a second
thermometer.
5. Measure indoor-air (entering indoor coil), wet-bulb tem-
perature with a sling psychrometer.
6. Locate outdoor temperature and evaporator entering air
wet-bulb temperature in Table 21. At this intersection note
the superheat.
7. Locate superheat temperature located in previous step and
vapor pressure in Table 22. At this intersection note
vapor-line temperature.
8. If unit has a higher vapor-line temperature than charted
temperature, add refrigerant until charted temperature is
reached.
9. If unit has a lower vapor-line temperature than charted
temperature, bleed refrigerant until charted temperature is
reached.
10. If outdoor-air temperature or pressure at vapor valve
changes, charge to new vapor-line temperature indicated on
chart.
SUBCOOLING CHARGING METHOD
1. Operate unit a minimum of 15 minutes before checking
charge.
TABLE 21—SUPERHEAT CHARGING TABLE
OUTDOOR TEMP (°F)
INDOOR COIL ENTERING AIR TEMP (°F WET BULB)
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.
TABLE 22—REQUIRED VAPOR TEMPERATURE (°F)
SUPERHEAT TEMP
(°F)
VAPOR PRESSURE AT SERVICE PORT (PSIG)
61.5 64.2 67.1 70.0 73.0 76.0 79.2 82.4 85.7
0 35 37 39 41 43 45 47 49 51
2 37 39 41 43 45 47 49 51 53
4 39 41 43 45 47 49 51 53 55
6 41 43 45 47 49 51 53 55 57
8 43 45 47 49 51 53 55 57 59
10 45 47 49 51 53 55 57 59 61
12 47 49 51 53 55 57 59 61 63
14 49 51 53 55 57 59 61 63 65
16 51 53 55 57 59 61 63 65 67
18 53 55 57 59 61 63 65 67 69
20 55 57 59 61 63 65 67 69 71
22 57 59 61 63 65 67 69 71 73
24 59 61 63 65 67 69 71 73 75
26 61 63 65 67 69 71 73 75 77
28 63 65 67 69 71 73 75 77 79
30 65 67 69 71 73 75 77 79 81
32 67 69 71 73 75 77 79 81 83
34 69 71 73 75 77 79 81 83 85
36 71 73 75 77 79 81 83 85 87
38 73 75 77 79 81 83 85 87 89
40 75 77 79 81 83 85 87 89 91
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