Lennox Elite XP16−024−230 Installation Instructions Manual page 27

OPTIMIZE CHARGE USING SUBCOOLING METHOD
USE
COOLING
MODE
60ºF
(15ºC)
USE
HEATING
MODE
SATº
LIQº –
SCº =
Figure 24. Using HFC−410A Subcooling Method
1. Check liquid and vapor line pressures. Compare pressures with either second−stage
heat or cooling mode normal operating pressures listed in table 7. Table 7 is a general
guide and expect minor pressures variations. Significant pressure differences may
indicate improper charge or other system problem.
2. Decide whether to use cooling or heating mode based on current outdoor ambient
temperature:
A
Use COOLING MODE
S
Outdoor ambient temperature is 60°F (15.5°C) and above.
S
Indoor return air temperature range is between 70 to 80°F (21−27°C). This
temperature range is what the target subcooling values are base upon in
tables 3 through 6.
If indoor return air temperature is not within reference range, set thermostat to
cooling mode and a setpoint of 68ºF (20ºC). This should place the outdoor unit
into second−stage (high−capacity) cooling mode. When operating and
temperature pressures have stabilized, continue to step 3.
B
Use HEATING MODE
S
Outdoor ambient temperature is 59°F (15.0°C) and below.
S
Indoor return air temperature range is between 65−75°F (18−24°C). This
temperature range is what the target subcooling values are base upon in
tables 3 through 6.
If indoor return air temperature is not within reference range, set thermostat to
heating mode and a setpoint of 77ºF (25ºC). This should place the outdoor unit
into second−stage (high−capacity) heating mode. When operating and
temperature pressures have stabilized, continue to step 3.
3. Read the liquid line pressure; then find its corresponding temperature pressure listed
in table 8 and record it in the SATº space to the left.
4. Read the liquid line temperature; record in the LIQº space to the left.
5. Subtract LIQº temperature from SATº temperature to determine subcooling; record
it in SCº space to the left..
6. Compare SCº results with tables 3 through 6 (either Heating or Cooling mode
column), also consider any additional charge required for line set lengths longer than
15 feet and/or unit matched component combinations (Add Charge column).
7. If subcooling value is:
A GREATER than shown for the applicable unit match component, REMOVE
refrigerant;
B LESS than shown for the applicable unit match component, ADD refrigerant.
8. If refrigerant is added or removed, repeat steps 3 through 6 to verify charge.
9. Close all manifold gauge set valves and disconnect gauge set from outdoor unit.
10. Replace the stem and service port caps and tighten as specified in Operating Service
Valves on page 2.
11. Recheck voltage while the unit is running. Power must be within range shown on the
nameplate.
when:
when:
Second Stage (High Capacity)
Page 27
XP16 SERIES