Lennox SSB*H4 Manual page 15

2 − Evacuate the system to remove as much of the moisture
as possible. Use dry nitrogen to pressurize the system
and check for leaks. Repair leaks, if possible.
3 − Use dry nitrogen to break the vacuum and install the pro-
vided filter drier in the system.
4 − Evacuate the system again. Then, weigh the appropriate
amount of R−410A refrigerant (listed on unit nameplate)
into the system.
5 − Monitor the system to determine the amount of moisture
remaining in the oil. Use test kit 10N46 to verify that the
moisture content is within the kit's dry color range. It
may be necessary to replace the filter drier several
times to achieve the required dryness level.
If system dryness is not verified, the compressor
will fail in the future.
Checking Charge
The outdoor unit should be charged during warm weather.
However, applications arise in which charging must occur in
the colder months. The method of charging is determined by
the unit's refrigerant metering device and the outdoor
ambient temperature.
Measure the liquid line temperature and the outdoor ambi-
ent temperature as outlined below:
1 − Connect the manifold gauge set to the service valves:
low pressure gauge to vapor valve service port
D
high pressure gauge to liquid valve service port
D
2 − Close manifold gauge set valves. Connect the center
manifold hose to an upright cylinder of R−410A .
3 − Set the room thermostat to call for heat. This will create
the necessary load for properly charging the system in
the cooling cycle.
4 − Record outdoor ambient temperature using a digital ther-
mometer.
5 − When the heating demand has been satisfied, switch the
thermostat to cooling mode with a set point of 68_F
(20_C). When pressures have stabilized, use a digital
thermometer to record the liquid line temperature.
6 − The outdoor temperature will determine which charging
method to use. Proceed with the appropriate charging
procedure.
Charge Using Weigh-in Method, Fixed Orifice or
TXV Systems
If the system is void of refrigerant, or if the outdoor ambient
temperature is cool, first, locate and repair any leaks and
then weigh in the refrigerant charge into the unit.
1 − Recover the refrigerant from the unit.
2 − Conduct leak check; evacuate as previously outlined.
3 − Weigh in the unit nameplate charge. If weighing facilities
are not available or if charging the unit during warm
weather, use one of the following procedures.
Charge Using the Subcooling Method –
Outdoor Temperature < 65°F (18°C)
When the outdoor ambient temperature is below 65°F
(18°C), use the subcooling method to charge the unit. Val-
ues from (table 5) are used for this procedure.
If necessary, restrict air flow through the outdoor coil to
achieve pressures in the 325−375 psig (2240−2585 kPa)
range. Higher pressures are necessary for checking the
charge. Block equal sections of air intake panels and move
obstructions sideways until the liquid pressure is in the
325−375 psig (2240−2585 kPa) range. See figure 10.
Blocking Outdoor Coil
1 − With the manifold gauge hose still on the liquid service
port and the unit operating stably, use a digital thermom-
eter to record the liquid line temperature.
2 − At the same time, record the liquid line pressure reading.
3 − Use a temperature/pressure chart (table 5) to determine
the saturation temperature for the liquid line pressure
reading.
4 − Subtract the liquid line temperature from the saturation
temperature (according to the chart) to determine sub-
cooling.
Page 15
Outdoor Temp. < 65ºF (18ºC)
*Outdoor coil should be blocked one
side at a time with cardboard or plastic
sheet until proper testing pressures are
reached.
cardboard or plastic sheet
*Four−sided unit shown.
FIGURE 10