Lennox T?CLASS TPA024S4 Unit Information page 22

WEIGH IN
Use method for adding initial refrigerant charge, and then use
WEIGH IN
CHARGING METHOD
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
SUBCOOLING
USE COOLING
MODE
60ºF (15º)
USE HEATING
MODE
SATº
LIQº –
SCº =
verifying refrigerant charge.
Adjust amount. for variation
in line set length listed on
line set length table below.
nameplate
+
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 15. Using Weigh In Method
1 Check the airflow as illustrated in Figure 14 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 in either
Table 5 or 6, (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 7 and record it in the SATº space.
8 Subtract LIQº temp. from SATº temperature to determine subcooling; record it in SCº space.
9 Compare SCº results with either Table 3 or 4, being sure to note any additional charge for line set and/or
match−up.
10 If subcooling value is greater than shown in the below table for the applicable unit size, remove refrigerant;
if less than shown, add refrigerant.
11 If refrigerant is added or removed, repeat steps 6 through 10 to verify charge.
Figure 16. Using Subcooling Method
CALCULATING SYSTEM CHARGE FOR OUTDOOR
UNIT VOID OF CHARGE
Total charge
=
Refrigerant Charge per Line Set Length
Ounces per 5 feet (g per 1.5 m)
Liquid Line
adjust from 15 feet (4.6 m) line set*
Set Diameter
3/8" (9.5 mm)
3 ounce per 5' (85 g per 1.5 m)
*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.
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
Page 22
SUBCOOLING
method for