Page 9
Charge Using Subcooling Method
Outdoor Temp. >65°F (18°C)
If you charge a fixed orifice system when the outdoor ambi-
ent is 65
F (18
C) or above, use the subcooling method to
charge the unit.
1. With the manifold gauge hose still on the liquid service
port and the unit operating stably, use a digital
thermometer to record the liquid line temperature.
2. At the same time, record the liquid line pressure reading.
3. Use a temperature/pressure chart for HCFC−22 to
determine the saturation temperature for the liquid line
pressure reading.
4. Subtract the liquid line temperature from the saturation
temperature (according to the chart) to determine
subcooling.
Saturation Temperature
F (
C)
Liquid Line Temperature
F (
C)
=
Subcooling Value
F (
C)
5. Compare the subcooling value with those in table 5 for
13ACD units with fixed orifices and table 6 for 13ACD
units with TXV. If subcooling is greater than shown,
recover some refrigerant. If subcooling is less than
shown, add some refrigerant.
TABLE 5
Subcooling Values For RFC Systems
Outdoor
Liquid Subcooling [+ 1
F (.6
C)]
Outdoor
Temp.
F(
C)
−018
−024
−030
−036
−042
−048
−1, −2
units
−048
−060
65 (18)
13
(7)
13
(7)
7 (4)
14
(8)
15
(8.3)
9 (5)
11
(6)
13
(7)
70 (21)
13
(7)
12
(6.7)
6
(3.3)
13
(7)
14
(8)
9 (5)
10
(5.6)
12
(6.7)
75 (24)
10
(5.6)
11
(6)
5 (3)
13
(7)
13
(7)
9 (5)
9 (5)
12
(6.7)
80 (27)
10
(5.6)
11
(6)
5 (3)
12
(6.7)
12
(6.7)
9 (5)
8
(4.5)
12
(6.7)
85 (29)
8
(4.5)
10
(5.6)
5 (3)
11
(6)
11
(6)
9 (5)
7 (4)
11
(6)
90 (32)
8
(4.5)
10
(5.6)
4
(2.2)
10
(5.6)
10
(5.6)
9 (5)
5
(2.8)
10
(5.6)
95 (35)
7 (4)
10
(5.6)
4
(2.2)
9 (5)
9 (5)
9 (5)
5
(2.8)
10
(5.6)
100 (38)
7 (4)
10
(5.6)
3 (2)
9 (5)
8
(4.5)
9 (5)
3
(1.7)
9 (5)
105 (41)
6
(3.3)
9 (5)
3 (2)
8
(4.5)
7 (4)
9 (5)
3
(1.7)
9 (5)
110 (43)
6
(3.3)
8
(4.5)
2 (1)
6
(3.3)
7 (4)
9 (5)
2
(1.1)
9 (5)
115 (45)
3 (2)
6
(3.3)
2 (1)
6
(3.3)
5 (3)
8
(4.5)
2
(1.1)
8
(4.5)
Charge using Subcooling Method
(TXV Systems)
Outdoor Temp.
t
65ºF (18ºC)
This charging procedure
should not be used
if ambient tem-
peratures are below 65ºF. For best results, indoor tempera-
ture should be 70ºF (21ºC) to 80ºF (26ºC).
1. Restrict the airflow (see figure 10) through the outdoor
coil to achieve pressures from 200−250 psig . These
higher pressures are necessary for checking the
charge. Block equal sections of air intake panels and
move coverings sideways until the liquid pressure is in
the above noted ranges.
Blocking Outdoor Coil
*Outdoor coil should be blocked one
side at a time with cardboard or plastic
sheet until proper testing pressures are
reached.
cardboard or plastic sheet
*Four−sided unit shown.
FIGURE 10
2. With the manifold gauge hose installed on the liquid
service port and the unit operating stably, use a digital
thermometer to record the liquid line temperature.
3. At the same time, record the liquid line pressure read-
ing.
4. Use a temperature/pressure chart for HCFC−22 refrig-
erant to determine the saturation temperature for the
liquid line pressure reading.
5. Subtract the refrigerant saturation temperature from
the liquid line temperature to determine subcooling.
Compare to table 6.
Saturation Temperature
F (
C)
Liquid Line Temperature
F (
C)
=
Subcooling Value
F (
C)
TABLE 6
Subcooling Values For TXV Systems
13ACD
−018
−024
−030
−036
−042
−048
−060
°F (C°)
8
(4.4)
8
(4.4)
4
(2.2)
7
(3.8)
10
(5.6)
9 (5)
14
(8)
Charge Using Approach Method (TXV Systems)
− Outdoor Temperature >65°F (18°C)
When charging an expansion valve system when the out-
door ambient temperature is 65
F (18
C) or above, it is
best to charge the unit using the approach method. Sub-
tract the outdoor ambient temperature from the liquid line
temperature to determine the approach temperature.
Liquid Line Temperature
F (
C)
Outdoor Ambient Temperature
F (
C)
=
Approach Value
F (
C)
The resulting difference (approach temperature) should
agree with the values given in table 7. If not, add refrigerant
to lower the approach temperature or recover refrigerant
from the system to increase the approach temperature.
