Lennox TPA036H4N4 Installation Instructions Manual page 24

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
Table 4. Adding Charge per Indoor Unit Match−Up using Subcooling Method
Use
cooling
mode
60ºF (15ºC)
Use
heating
mode
SATº
LIQº –
SCº =
506650−01
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 21. Weigh In Method
1 Check the airflow using figure 20 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 6, (Table 6 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
Target 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
Target subcooling 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 table 7) 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 table below, remove refrigerant; if less than
shown, add refrigerant.
11 If refrigerant is added or removed, repeat steps 5 through 10 to verify charge.
CALCULATING SYSTEM CHARGE FOR
OUTDOOR UNIT VOID OF CHARGE
Additional charge specified per indoor
unit match−ups starting on page 25.
+
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.
When the outdoor ambient temperature is below 60°F (15°C).
Page 24
SUBCOOLING
method for
=
Total charge