Lennox Merit Series 14HPX Installation Instructions Manual page 18

WEIGH IN
Use method for adding initial refrigerant charge, and then use
verifying refrigerant charge.
WEIGH IN
If the system is void of refrigerant, first, locate and repair any leaks and then weigh in the refrigerant charge into the
unit. To calculate the total refrigerant charge:
Amount specified on nameplate
SUBCOOLING
USE COOLING
MODE
60ºF (15º)
USE HEATING
MODE
SATº
LIQº –
SCº =
506377−01 11/09
Adjust amount. for variation in line set
length listed on line set length table below.
+
Refrigerant Charge per Line Set Length
Liquid Line
Set Diameter
3/8" (9.5 mm)
*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.
NOTE Insulate liquid line when it is routed through areas where the surrounding ambient temperature
could become higher than the temperature of the liquid line or when pressure drop is equal to or greater
than 20 psig.
NOTE The above nameplate is for illustration purposes only. Go to actual nameplate on outdoor unit for
charge information.
Figure 10. Weigh In Method
1 Check the airflow as illustrated in figure 9 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 Normal Operating Pressures table 10,
(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
subcooling values in table below 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). When pressures have stabilized, continue with step 6.
Using heating mode
values in table below 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). 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 11 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 table 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 3 through 8 for the applicable unit, remove refrigerant;
if less than shown, add refrigerant.
11 If refrigerant is added or removed, repeat steps 5 through 10 to verify charge.
Figure 11. Subcooling Method
Page 18
SUBCOOLING
CALCULATING SYSTEM CHARGE FOR
OUTDOOR UNIT VOID OF CHARGE
Additional charge specified per indoor
unit match−ups starting on Page 19.
+
Ounces per 5 feet (g per 1.5 m)
adjust from 15 feet (4.6 m) line set*
3 ounce per 5' (85 g per 1.5 m)
When the outdoor ambient temperature is 60°F (15°C) and above. Target
When the outdoor ambient temperature is below 60°F (15°C). Target subcooling
method for
Total charge
=