GMC 1976 ZEO 6083 Maintenance Manual page 71

1- 54 AIR CONDITIONING SYSTEM
ment to provide a positive pressure advantage to
overcome system pressure equalization .
GAUGE SET
The gauge set is an integral part of the Charging
Station. It is used when purging, evacuating, charg-
ing or diagnosing trouble in the system . The gauge
at the left is known as the low pressure gauge. The
face is graduated into pounds of pressure and, in the
opposite direction, in inches of vacuum . This is the
gauge that should always be used in checking pres-
sures on the low pressure side of the system . When
all parts of the system are functioning properly the
refrigerant pressure on the low pressure side never
falls below 0 pounds pressure . However, several ab-
normal conditions can occur that will cause the low
pressure to fall into a partial vacuum . Therefore, a
low pressure gauge is required .
The high pressure gauge is used for checking
pressures on the high pressure side of the system .
The hand shutoff valves on the gauge manifold
do not control the opening or closing off of pressure
to the gauges . They merely close each opening to the
center connector and to each other. During most
diagnosing and service operation, the valves must be
closed . Both valves will be open at the same time
during purging, evacuating and charging operations .
The charging station provides two flexible lines
for connecting the gauge set to the system compo-
nents.
VACUUM PUMP
A vacuum pump should be used for evacuating
air and moisture from the air conditioning system .
The vacuum pump (figure 26), is a component
part of Charging Station described previously .
CAUTION :
The following precautions
should be observed relative to the operation
and maintenance of this pump :
1 . Make sure dust cap on discharge outlet of
vacuum pump is removed before oerating .
2 . Keep all openings capped when not in use to
avoid moisture being drawn into the system.
3 . Oil should be changed after every 250 hours of
normal operation.
To change oil, simply unscrew hex nut located on
back side of pump, tilt backward and drain out oil.
Recharge with 8 ounces of vacuum pump oil Frigi
daire 150 or equivalent . If you desire to flush out the
pump, use this same type clean oil. Do not use sol-
vent . Improper lubrication will shorten pump life .
4. If this pump is subjected to extreme or pro-
longed cold, allow it to remain indoors until oil has
reached approximate room temperature. Failure to
warm oil will result in a blown fuse .
5. A five ampere time delay cartridge fuse has
been installed in the common line to protect the
windings of the compressor . The fuse will blow if an
excessive load is placed on the pump . In the event the
fuse is blown, replace with a five ampere time delay
fuse.
Do not use a substitute fuse
as it will result in
damage to the starting windings .
6. If the pump is being utilized to evacuate a
burnt-out system, a filter must be connected to the
intake fitting to prevent any sludge from contaminat
ing the working parts, which will result in malfunc-
tion of the pump .
7. Do not use the vacuum pump as an air com-
pressor.
LEAK TESTING THE SYSTEM
Whenever a refrigerant leak is suspected in the
system or a service operation performed which re-
sults in disturbing lines or connections, it is advisable
to test for leaks. Common sense should be the gov-
erning factor in performing any leak test, since the
necessity and extent of any such test will, in general,
depend upon the nature of the complaint and the
type of service performed on the system .
LEAK DETECTOR
Tool J-6084 (figure 27) is a propane gas-burning
torch which is used to locate a leak in any part of the
system . Refrigerant gas drawn into the sampling
tube attached to the torch will cause the torch flame
to change color in proportion to the size of the leak .
Propane gas fuel cylinders used with the torch are
readily available commercially throughout the coun-
try.
WARNING: DO NOT USE LIGHTED DETECTOR
IN ANY PLACE WHERE COMBUSTIBLE OR EX-
PLOSIVE GASES, DUSTS OR VAPORS MAY BE
PRESENT .
OPERATING DETECTOR
1 . Determine if there is sufficient refrigerant in
the system for leak testing.