Lennox International Inc. 2SCU13 User Manual
Page 11
# 48283B006
Page 11
Charge Using Weigh-In Method (Fixed Orifice/TXV
Systems)
If the system is void of refrigerant, or if the outdoor ambient
temperature is cool, first locate and repair any leaks then
use the weigh-in method to charge the unit.
1. Recover the refrigerant from the unit.
2. Conduct a leak check, then evacuate as previously
outlined.
3. Weigh in the charge according to the total amount
shown on the unit nameplate.
If weighing facilities are not available or if unit is being
charged during warm weather, follow one of the other
procedures outlined below.
Charge Using Subcooling Method (Fixed Orifice/TXV
Systems) – Outdoor Temperatures 65°F or Above
If charging a fixed orifice or TXV system when the outdoor
ambient temperature is 65°F or above, the subcooling
method can be used to charge the unit.
1. With the manifold gauge hose on the liquid service
port and the unit operating stably, use a digital ther-
mometer 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 satura-
tion temperature (according to the chart) to determine
subcooling.
3. Use a temperature/pressure chart for HCFC-22 to
determine the saturation temperature for the suction
line pressure reading.
4. Subtract the saturation temperature (according to the
chart) from the suction line temperature to determine
the superheat.
_____ °
Suction Line Temperature °F
_____ °
Saturation Temperature °F
_____ °
Superheat Value °F
–
=
_____ °
Saturation Temperature °F
_____ °
Liquid Line Temperature °F
_____ °
Subcooling Value °F
–
=
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6
3
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6
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5
6
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7
4
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9
2
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8
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9
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7
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3
6
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6
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8
8
Subcooling Values for
Fixed Orifice or TXV Systems
Table 6
5. Compare the subcooling value with those shown in
Table 6. If subcooling is greater than shown, recover
some refrigerant. If subcooling is less than shown,
add some refrigerant.
Charge Using Superheat Method (Fixed Orifice
Systems) – Outdoor Temperatures 65°F or Above
1. With the manifold gauge hose on the suction service
port and the unit operating stably, use a digital ther-
mometer to record the suction line temperature.
2. At the same time, record the suction line pressure
reading.
5. Compare the superheat value with those shown in
Table 7 on page 12. If superheat is greater than
shown, add some refrigerant. If superheat is less than
shown, recover some refrigerant.
Charge Using Approach Method (TXV Systems)
– Outdoor Temperatures 65°F or Above
The following procedure is intended as a general guide
and is for use on expansion valve systems only. For best
results, indoor temperature should 70°F to 80°F. Monitor
system pressures while charging.
1. Record outdoor ambient temperature using a digital
thermometer.
2. Attach high pressure gauge set and operate unit for
several minutes to allow system pressures to stabilize.
3. Compare stabilized pressures with those provided in
Table 9 on page 13. Minor variations in these pres-
sures may be expected due to differences in installa-
tions. Significant differences could mean that the
system is not properly charged or that a problem
exists with some component in the system.