32
5.10.2
Procedure
During
vacuum
drying,
a
vacuum
pump
is
used
to
lower
the
pressure
in
the
piping
to
the
extent
that
any
moisture
present
evaporates.
At
5mmHg
(755mmHg
below
typical
atmospheric
pressure)
the
boiling
point
of
water
is
0°C.
Therefore
a
vacuum
pump
capable
of
maintaining
a
pressure
of
‐
756mmHg
or
lower
should
be
used.
Using
a
vacuum
pump
with
a
discharge
in
excess
of
4L/s
and
a
precision
level
of
0.02mmHg
is
recommended.
Caution
Before
performing
vacuum
drying,
make
sure
that
all
the
outdoor
unit
stop
valves
are
firmly
closed.
Once
the
vacuum
drying
is
complete
and
the
vacuum
pump
is
stopped,
the
low
pressure
in
the
piping
could
suck
vacuum
pump
lubricant
into
the
air
conditioning
system.
The
same
could
happen
if
the
vacuum
pump
stops
unexpectedly
during
the
vacuum
drying
procedure.
Mixing
of
pump
lubricant
with
compressor
oil
could
cause
compressor
malfunction
and
a
one
‐
way
valve
should
therefore
be
used
to
prevent
vacuum
pump
lubricant
seeping
into
the
piping
system.
Procedure
The
vacuum
drying
procedure
is
as
follows:
Step
1
Connect
the
blue
(low
pressure
side)
hose
of
a
pressure
gauge
to
the
master
unit
gas
pipe
stop
valve,
the
red
(high
pressure
side)
hose
to
the
master
unit
liquid
pipe
stop
valve
and
the
yellow
hose
to
the
vacuum
pump.
Step
2
Start
the
vacuum
pump
and
then
open
the
pressure
gauge
valves
to
start
vacuum
the
system.
After
30
minutes,
close
the
pressure
gauge
valves.
After
a
further
5
to
10
minutes
check
the
pressure
gauge.
If
the
gauge
has
returned
to
zero,
check
for
leakages
in
the
refrigerant
piping.
Step
3
Re
‐
open
the
pressure
gauge
valves
and
continue
vacuum
drying
for
at
least
2
hours
and
until
a
pressure
difference
of
756mmHg
or
more
has
been
achieved.
Once
the
pressure
difference
of
at
least
756mmHg
has
been
achieved,
continue
vacuum
drying
for
2
hours.
Step
4
Close
the
pressure
gauge
valves
and
then
stop
the
vacuum
pump.
After
1
hour,
check
the
pressure
gauge.
If
the
pressure
in
the
piping
has
not
increased,
the
procedure
is
finished.
If
the
pressure
has
increased,
check
for
leakages.
After
vacuum
drying,
keep
the
blue
and
red
hoses
connected
to
the
pressure
gauge
and
to
the
master
unit
stop
valves
,
in
preparation
for
refrigerant
charging
(see
Installation
Manual,
8
“Charging
Refrigerant”).
Figure
3
‐
5.14:
Vacuum
drying
Pressure
gauge
Notes
for
installers
Master
unit
Slave
unit
Slave
unit
Yellow
hose
Gas
pipe
stop
valve
Liquid
pipe
stop
valve
Field
piping
Stop
valve
service
port
Pressure
gauge
Blue
hose
1
2
Red
hose
1
2
Vacuum
pump