Air
Conditioning
System
Manual
-
------
Rolls-Royce
&
Bentley------------
Action
to
be taken:
1.
Check the suction side
of
the system for
leaks and rectify. Discharge the refrigerant,
renew the dehydration charge in the drier,
and
evacuate. Re-charge with the correct
quantity
of
new refrigerant.
2.
Discharge the refrigerant and re-charge with
the correct quantity.
Head
pressure
correct
but
suction
preuure
low
Probable causes are:
I. Blower motor or motors not functioning.
2.
Restricted filter-drier.
3.
The
Superheat setting
of
the expansion
valve
or
valves too high.
Action to be taken:
I. Check the blower motor operation.
2.
Test the filter-drier and renew it
if
the
filters
are choked.
3.
Check the superheat settings.
Pressure
tests
Switch off
and
install the manifold gauge set
with both its valves firmly closed. Remove the
protection caps from the compressor service
valves
and
just
crack
open
both valves
by
rotat-
ing one half-turn clockwise.
Warning:
During these tests it is essential that
the compressor service valves are not
fully open, as this closes the system
delivery and intake valves and could
possibly cause
an
explosion.
Run
the engine at fast idle wilh the refrigeration
system operating and the blower motors
at
full
speed.
Turn
the compressor service valves anti-
clockwise to damp
out
any gauge fluctuation.
The
compound
gauge reading should be 20
to
35
lb.!sq.in. With the following ambient air
Page26
temperatures (temperature
in
the shade) the
pressure gauge reading should
be:-
60°F. (15.6°C.)
I00-150
lb.I
sq.in.
so°F. (24.7°C.)
140-190 lb./sq.in.
100°F. (37.8°C.)
180-240 lb.I sq.in.
l l0°F. (43.3°C.)
230-280 lb./sq.in.
Superheat
test
The system may be checked for correct
operation
by
testing the upper
and
lower
evaporators individually as follows: -
Attach the thermometer RH.530 to the suction
pipe from the evaporator. Cover the thermo-
meter bulb and the pipe with a thick cloth
to
provide insulation from atmospheric temperature,
leaving the scale visible. Allow the engine to run
for a
few
minutes
at
1,200-1,800 r.p.m. with the
refrigeration system operating. Read the thermo-
meter,
and
the compound gauge
at
the com-
pressor.
Add
3 lb./sq.in. to the gauge reading
to
compensate for pressure drop in the suction line.
Ref
er
to the following table to obtain the
saturation temperature corresponding to this
pressure and subtract this figure from the thermo-
meter reading. The result should
be
between
8°
and
15
° F. which is termed the
'Superheat
Reading'.
Having obtained the correct values, any
inefficiency
can
only be attributed to poor air
delivery. In such cases, check the blower motor
operation and ensure that the inlet and outlet
ducts are unobstructed.
TO DISCHARGE
THE
REFRIGERANT
The
refrigerant must be discharged
from
the
system
prior
to breaking any
joint,
except the
compressor unit joints which are protected
by
the
service valves.
Do
not discharge in the presence
of
an open flame;
the refrigerant does not burn, but decomposes
to
form a poisonous gas.
Remove the protective caps from the com-
pressor service valves. Just 'crack' the high
pressure valve in a clockwise direction, allowing
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