Page 13
WHEN TO CHARGE?
Warm weather best
Can charge in colder weather
CHARGE METHOD? Determine by:
Metering device type
Outdoor ambient temperature
REQUIREMENTS:
Sufficient heat load in structure
Indoor temperature between 70-80ºF (21−26ºC)
Manifold gauge set connected to unit
Thermometers:
− to measure outdoor ambient temperature
− to measure liquid line temperature
− to measure vapor line temperature
TXV RFC
APPROACH OR
SUBCOOLING
WEIGH-IN SUPERHEAT
Which
metering
device?
Below 65ºF
(18ºC)?
Above 40ºF
(4ºC)?
Above 65ºF
(18ºC)?
START: Determine how refrigerant is metered
FIGURE 13 When to charge, method to use, conditions & equipment required
IMPORTANT
Before attempting to charge any system, confirm proper airflow across the in-
door coil. Airflow over the indoor coil can be determined by measuring the stat-
ic pressure drop across the coil and comparing it with the factory table pro-
vided in the indoor coil installation instructions.
If value is greater than
shown, add refrigerant;
if less than shown,
remove refrigerant.
ABOVE
Outdoor
ambient 40ºF
(4ºC)?
START: Measure outdoor ambient temperature
BELOW
Check Liquid and Vapor line pressures
Compare unit pressures with Normal
Operating Pressures table 4, page 15.
(Table 4 is a general guide. Expect minor pressures
variations. Significant differences may mean improp-
er charge or other system problem.)
Use SUPERHEAT to correctly charge unit
or to verify the charge is correct.
NOTE − Do not at-
tempt to charge sys-
tem where a dash ap-
pears, system could
be overcharged. Su-
perheat is taken at va-
por line service port.
Vapor line superheat
must never be less
than 5ºF at the vapor
line service port.
USE WEIGH-IN METHOD
Weigh-in or remove refriger-
ant based upon line length
SHº (Superheat) Values (+/−5ºF)
Wet Bulb (air entering indoor coil)
ºF* 50 52 54 56 58 60 62 64 66 68 70 72 74 76
40 15 18 20 23 26 29 32 34 38 41 43 46 48 51
45 13 16 18 21 24 27 30 33 36 39 41 44 46 49
50 11 14 16 19 22 25 28 31 34 37 39 42 44 47
55 9 12141720232730333638404244
60 7 10121518212427303335384043
65 - 6 10 13 16 19 21 24 27 30 33 36 38 41
70 - - 7 1013161921242730333639
75 - - - 6 9 121518212428313437
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 10 14 18 22 25 29
100 --------81216212428
105 - - - - - - - - 5 9 13 17 22 26
110 ---------611152025
115 ----------8141824
* Dry−bulb temperature (ºF) of entering outdoor ambient air.
If refrigerant added or
removed, retest to
confirm that unit is
properly charged
SUPERHEAT METHOD
Set thermostat to call for heat (must have a
cooling load between 70-80ºF (21−26ºC)
Connect gauge set
When heat demand is satisfied, set
thermostat to call for cooling
Allow temperatures and pressures to
stabilize
Record vapor line pressure; use value to
determine saturation temperature
(table 5 on page 15) SATº =
Record vapor line
temperature VAPº =
Subtract to determine superheat (SHº):
VAPº − SATº = SHº
Record the wet bulb temperature (air
entering indoor coil) WB =
Record outdoor ambient temperature
Compare results with table
FIGURE 14 Charging RFC units with Superheat Method
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