Lennox 13ACC Series Manual page 8

C − Evacuating the System
1− Attach gauge manifold. Connect vacuum pump (with vac
uum gauge) to center port of gauge manifold. With both
manifold service valves open, start pump and evacuate
indoor coil and refrigerant lines.
IMPORTANT
A temperature vacuum gauge, mercury vacuum
(U−tube), or thermocouple gauge should be used.
The usual Bourdon tube gauges are not accurate
enough in the vacuum range.
IMPORTANT
The compressor should never be used to evacu
ate a refrigeration or air conditioning system.
2− Evacuate the system to 29 inches (737mm) vacuum.
During the early stages of evacuation, it is desirable to
stop the vacuum pump at least once to determine if there
is a rapid loss of vacuum. A rapid loss of vacuum would
indicate a leak in the system and a repeat of the leak test
ing section would be necessary.
3− After system has been evacuated to 29 inches
(737mm), close gauge manifold valves to center port,
stop vacuum pump and disconnect from gauge man
ifold. Attach an upright nitrogen drum to center port of
gauge manifold and open drum valve slightly to purge
line at manifold. Break vacuum in system with nitro
gen pressure by opening manifold high pressure
valve. Close manifold high pressure valve to center
port.
4− Close nitrogen drum valve and disconnect from
gauge manifold center port. Release nitrogen pres
sure from system.
5− Connect vacuum pump to gauge manifold center
port. Evacuate system through manifold service
valves until vacuum in system does not rise above
.5mm of mercury absolute pressure or 500 microns
within a 20−minute period after stopping vacuum pump.
6− After evacuation is complete, close manifold center port,
and connect refrigerant drum. Pressurize system
slightly with refrigerant to break vacuum.
D − Charging
The condensing 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 suction valve service port; high
pressure gauge to liquid valve service port. Connect
the center manifold hose to an upright cylinder of
HCFC 22. Close manifold gauge set valves.
2. −Set the room thermostat to call for heat. This will create
the necessary load for properly charging the system in
the cooling cycle.
3. −Use a digital thermometer to record the outdoor ambi
ent temperature.
4. −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.
5. −The outdoor temperature will determine which charg
ing method to use. Proceed with the appropriate charg
ing procedure.
Weighing in the Charge Fixed Orifice or
TXV Systems
If the system is void of refrigerant, or if the outdoor ambient
temperature is cool, the refrigerant charge should be
weighed into the unit according to the total amount shown
on the unit nameplate. This may be done after any leaks
have been repaired. If weighing facilities are not available
or if unit is being charged during warm weather, follow one
of the other procedures outlined below.
1 − Recover the refrigerant from the unit.
2 − Conduct a leak check, then evacuate as previously
outlined.
3 − Weigh in the factory charge according to the amount
recorded on the outdoor unit nameplate.
Page 8
Outdoor Temp < 65_F (18_C)