Chevrolet Light Duty Truck 1973 Service Manual page 68

1A-42 HEATER A N D AIR C O N D IT IO N IN G
direction, in inches of vacuum. This is the gauge that
should always be used in checking pressures 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 abnormal 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 components.
VACUUM PUMP
A vacuum pump should be used for evacuating air and
moisture from the air conditioning system.
The vacuum pump (fig. 47), is a component part of
Charging Station J-8393, described previously.
The following precautions should
CAU TIO N :
be observed relative to the operation and
maintenance o f this pump:
• Make sure dust cap on discharge outlet of
vacuum pump is removed before operating.
• Keep all openings capped when not in use to
avoid moisture being drawn into the system.
• 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 (fig. 47). Recharge with 8 ounces of vacuum
pump oil Frigidaire 150 or equivalent. If you
desire to flush out the pump, use this same type
clean oil. Do not use solvent. Im proper
Lubrication will shorten pump life.
• If this pump is subjected to extreme or
prolonged cold, allow it to remain indoors until
oil has reached approximate room temperature.
Failure to warm oil will result in a blown fuse.
• 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.
as it will result in damage to the starting
fuse
windings.
Do not use a substitute
FIVE AMP
TIME DELAY
FUSE
CORD TO
110 AC SOURCE
Fig. 47-Vacuum Pump
• 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
contaminating the working parts, which will
result in malfunction of the pump.
• Do not use the vacuum pump as an air
compressor.
LEAK TESTING THE SYSTEM
Whenever a refrigerant leak is suspected in the system or
a service operation performed which results in disturbing
lines or connections, it is advisable to test for leaks.
PUMP PUMP DISCHARGE
INLET OUTLET
LIGHT DUTY TRUCK SERVICE MANUAL