Lennox XP17-024-230-01 Installation And Service Procedure page 79

SUBCOOLING
CHARGING METHOD
USE
COOLING
MODE
60ºF
(15ºC)
USE
HEATING
MODE
SATº
LIQº –
SCº =
Figure 50. Using HFC-410A Subcooling Method — Second Stage (High Capacity)
XP17
1. Check the airflow as illustrated in figure 48 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 heat or cooling
mode normal operating pressures on unit charging sticker, Normal Operating
Pressures, 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 MODE
and above. Target subcooling values (second stage - high capacity) on the charging
sticker 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 MODE
(15°C). Target subcooling values (second-stage - high capacity) on the charging
sticker 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 temper­
ature/ pressure chart listed in table 18 and record it in the SATº space.
8. Subtract LIQº temperature from SATº temperature to determine subcooling; record
it in SCº space.
9. Compare SCº results with unit charging sticker, being sure to note any additional
charge for line set and/or match-up.
10. If subcooling value is greater than shown on unit charging sticker for the applicable
unit, remove refrigerant; if less than shown, add refrigerant.
11. If refrigerant is added or removed, repeat steps 5 through 6 to verify charge.
12. Disconnect gauge set and re-install both the liquid and suction service valve caps.
— When the outdoor ambient temperature is 60°F (15°C)
— When the outdoor ambient temperature is below 60°F
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