GMC 4000 Series Service Manual page 90

12. Allow engine to run for 10 minutes, or until
stabilized.
NOTE: If at any time during test.com pressor
head pressure exceeds 375 psi, discontinue test
and check the following:
a. Engine cooling system .
b. Restricted receiver and liquid indicator
assembly.
c. Air in refrigeration system or overcharge
of refrigerant.
d. Insufficient auxiliary fan air on radiator
and condenser.
13. At the end of this time record the following:
a. Ambient air at condenser.
b. Wet bulb temperature in auxiliary fan air
stream.
c. Compressor head pressure.
d. Refrigerant test fitting gauge pressure.
e. Center outlet temperature.
Compare above with system pressures and
temperature shown on "Operational Test Data
Chart" (fig. 9). If not within the lim its shown, re­
fer to the "Insufficient Cooling Diagnosis Chart"
for possible cause of sub-standard performance.
Reference should be made in the order listed with
head pressure first, if not within "Operational
Test Data Chart" lim its, then check suction throt­
tling valve inlet pressure and finally center outlet
temperature.
NOTE: For altitude levels at or near sea level,
set the suction throttling valve as specified (23
psig). For higher levels, set valve 1/2 lb. per sq.
in. higher for each 1,000 feet of elevation.
14. Remove charging manifold gauge set, test
fitting gauge, and install the fitting caps.
DEPRESSURIZING THE SYSTEM
Any time the system is to be opened, it must
first be depressurized. Depressurize the system
as follows:
NOTE: Install gauge set to com pressor gauge
fittings (fig. 11).
1. Remove caps from gauge fittings at com­
p ressor.
2. With both valves on the manifold gauge set
J-5725-04 closed (clockwise), attach manifold hoses
to com pressor fittings, using J-5420 Schrader
valve adapter at the suction gauge fitting and J-
9459 Schrader valve adapter at the discharge gauge
fitting.
3. Crack open the high pressure valve on mani­
fold gauge set to allow slow escape of refrigerant
from the system through the manifold gauge set
and out the center fitting and hose. (Place end of
hose in clean container.) If oil drips from the hose
into the container, refrigerant is escaping too
rapidly.
G M C S E R V I C E M A N U A L
erant has escaped) close valves on manifold gauge
set by turning valve clockwise.
ized and opened for service, some air will enter
the lines regardless of how quickly the openings
are capped. In order to remove this air and as
much as possible of the moisture it contains, the
complete system must be "evacuated." Evacuating
is merely the process of removing all air from the
system , thereby creating a vacuum in the system.
PREPARATION FOR EVACUATING
COMPLETE SYSTEM
calibration, with the gauge disconnected from the
refrigeration system . Be sure that the pointer on
the gauge indicates to the center of "O." Tap the
gauge a few tim es lightly to be sure pointer is not
sticking. If necessary, calibrate as follows:
ly with one hand, carefully force pointer in the
proper direction in the proper amount to position
the pointer through the center of the "O" position.
Tap gauge a few tim es to be sure pointer on gauge
is not sticking. Replace gauge cover.
compressor fittings, connect as follows (refer to
fig. 11):
turning clockwise.
pressor.
time, the valve core in each compressor gauge
fitting can be unseated using Tool J-22132-01. The
gauge lines are then connected to the tool fittings.
Turn tool knobs counterclockwise to unseat cores.
end of hose from suction valve low pressure gauge
and connect this adapter fitted hose to the com­
pressor suction gauge fitting or to Tool J-22132-01
(if used).
end of hose from com pressor gauge and connect
this adapter fitted hose to the discharge gauge fit­
ting or Tool J-22132-01 (if used).
fitting of the gauge set and attach the other end of
this hose to the vacuum pump J-5428-03 (fig. 11).
AIR CONDITIONING
4. When hissing ceases (indicating all refrig­
EVACUATING THE SYSTEM
When the refrigeration system is depressur­
CAUTION: Under no circumstances
should alcohol be used in the system in an
attempt to remove moisture, regardless
of the successful use of alcohol in other
refrigeration system s.
1. Check the low pressure gauge for proper
a. Remove the cover from the gauge.
b. Holding gauge pointer adjusting screw firm ­
2. If gauge set is not already connected to
a. Close hand shut-off valves on gauge set by
b. Remove caps from gauge fittings at com­
NOTE: To shorten evacuating and charging
c. Attach Schrader valve adapter J-5420 to
d. Attach Schrader valve adapter J-9459 to
3. Attach a flexible gauge hose to the center
Sec. 1
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