Page 18
505331M 06/09
WEIGH IN
1. Check Liquid and suction line pressures
2. Compare unit pressures with Table 8,
Normal Operating Pressures.
3. Conduct leak check; evacuate as
previously outlined.
4. Weigh in the unit nameplate charge plus
any charge required for line set differences
over feet.
Liquid Line
Set Diameter
Ounces per 5 feet (g per 1.5 m)
adjust from 15 feet (4.6 m) line set*
3/8" (9.5 mm)
3 ounce per 5’ (85 g per 1.5 m)
NOTE − *If line length is greater than 15 ft. (4.6 m), add this
amount. If line length is less than 15 ft. (4.6 m), subtract this
amount.
Refrigerant Charge per Line Set Length
This nameplate is for illustration purposes
only. Go to actual nameplate on outdoor
unit for charge information.
Figure 31. Using Weigh In Method
1 Check the airflow as illustrated in Figure 30 to be sure the indoor airflow is as required.
(Make any air flow adjustments before continuing with the following procedure.)
2 Measure outdoor ambient temperature; determine whether to use cooling mode or
heating mode to check charge.
3 Connect gauge set.
4 Check liquid and vapor line pressures. Compare pressures with either cooling or heating
mode normal operating pressures in Table 8 (second stage − high capacity).
NOTE − The reference table is a general guide. Expect minor pressure variations. Significant
differences may mean improper charge or other system problem.)
5 Set thermostat for heat/cool demand, depending on mode being used:
Using cooling modeWhen the outdoor ambient temperature is 60°F (15°C) and above.
Target subcooling values (second stage − high capacity) in Table 8 are based on 70 to 80°F
(21−27°C) indoor return air temperature; if necessary, operate heating to reach that
temperature range; then set thermostat to cooling mode setpoint to 68ºF (20ºC) which should
call for second stage (high capacity) cooling. When pressures have stabilized, continue with
step 6.
Using heating modeWhen the outdoor ambient temperature is below 60°F (15°C). Target
subcooling values (second stage − high capacity) in Table 8 are based on 65−75°F (18−24°C)
indoor return air temperature; if necessary, operate cooling to reach that temperature range;
then set thermostat to heating mode setpoint to 77ºF (25ºC) which should call for second stage
(high capacity) heating. When pressures have stabilized, continue with step 6.
6 Read the liquid line temperature; record in the LIQº space.
7 Read the liquid line pressure; then find its corresponding temperature in the temperature/
pressure chart listed in Table 9 and record it in the SATº space.
8 Subtract LIQº temp. from SATº temp. to determine subcooling; record it in SCº space.
9 Compare SCº results with tables below, being sure to note any additional charge for line set
and/or match−up.
10 If subcooling value is greater than shown in Tables 4 through 7 for the applicable unit, remove
refrigerant; if less than shown, add refrigerant.
11 If refrigerant is added or removed, repeat steps 4 through 10 to verify charge.
USE COOLING
MODE
USE HEATING
MODE
60ºF (15º)
SATº
LIQº –
SCº =
SUBCOOLING
Figure 32. Using Subcooling Method Second Stage (High Capacity)
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