29
will swing drastically and the discharge pressure is very high. In the both
cases, stop the compressor at once, and if technique is available, open the
cylinder cover and check up the valve block, repair it, or replace it with a
new one,
C. Sudden stop of Compressor during Its Running
The cause
of
sudden
stop
of
a
compressor
during
its
running
is mostly
that the
gas
suction
pressure
and/or
discharge
pressure
exceed their
respective
prescribed
ranges,
thus
making
a
pressure-operated
protective
relay shut
off
the
power
to
the
compressor
and
stop
it.
In
the
following we
discuss
mainly
the
reasons
for
causing
excessively
high
gas
discharge
pressure and low
suction pressure.
1) Stoppage due to
excessively high
gas discharge pressure
A) Too much refrigerant charged into the system
Analysis of Trouble
The phenomenon,
such
as
loose
frosting
and
poor
refrigerating effect,
may occur
if
excessive
refrigerant
has
been
charged
into
the
system.
Superfluous
refrigerant
will
occupy
a
certain
space
of
the
evaporator, thus
reduce its
heat
dissipating
area,
and
the
phenomenon
of "liquid
striking$
may occur,
too.
Meanwhile,
dew
or
frost
condensation
may
occur on the
gas return
tube,
and
the
gas
discharge
pressure
will
obviously
rise,
when it
reaches
the
threshold
value,
the
protective
relay
will
actuate
and
shut off
the power supply to the
compressor.
Remedy
Open
the
tubing,
re-evacuate
and
then
charge
the
system
with
a proper
quantity of refrigerant.
b) Air left in the system
Analysis of Trouble
The residual
air
in
the
system
will
circulate
together
with
the
refrigerant
in the system.
The
major
symptoms
caused
by
this
residual
air
is higher
gas discharge
pressure,
higher
discharged
gas
temperature
(the gas
discharge
tubing
is
considerably
hot
when
you
feel
it
with
your
hand), and
poorer refrigerating
effect.
Furthermore,
the
gas
discharge
pressure will
exceed its
normal
value
when
the
compressor
has
run
for
a
period not too
long, thus making the protective relay
actuate and bring to a stoppage.
Remedy
Check
up
how
the
air
has
been
left
in
the
refrigerating
system.
Generally,
there
are
two
possibilities:
one
is
that
the
air
has
been
sucked
into the
system
when
repairing
due
to
carelessness,
or
it
has
not been
purged out
totally
when
evacuating
the
system;
the
other
is
that
there are
leak points at the low pressure end of the refrigerating system. Leak points
appear mostly in those low temperature parts or assemblies, because the
evaporation temperature is lower for such low temperature devices,
especially at the low pressure end, it is easier for the air goes into the
system. Once it has been ascertained that air does exist in the system, you
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