Chevrolet 10 1971 Series Chassis Service Manual page 32

HEATER AND AIR CONDITIONING 1A-14
The pump mount is such that the dealer may use his
own vacuum pump. The gauges and manifold are in com­
mon use. Thus a current air conditioning dealer can use
the equipment on hand and avoid duplication.
GAUGE SET
The gauge set (fig. 22) is an integral part of the J-8393
Charging Station. It is used when purging, evacuating,
charging 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.
should always be used in checking pressures on the low
pressure side of the system. When all parts of the sys­
tem are functioning properly the refrigerant pressure on
the low pressure side never falls below 0 pounds pres­
sure. However, several abnormal conditions can occur
that will cause the low pressure to fall into a partial vac­
uum. Therefore, a low pressure gauge is required.
The high pressure gauge is used for checking pres­
sures 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.
and service operations, 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.
V A C U U M PUMP
A vacuum pump should be used for evacuating air and
moisture from the air conditioning system.
The vacuum pump (fig. 23) is a component part of
Charging Station J-8393, described previously. The fol­
lowing precautions should be observed relative to the
operation and maintenance of 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.
1
L O W PRESSU RE
C O N T R O L
3
V A C U U M
C O N T R O L
Fig. 2 2 — Charging Station G auge Set
This is the gauge that
During most diagnosing
H IG H PR ESSU R E
C O N T R O L
4
F R E O N
C O N T R O L
FIVE A M P
TIME D E L A Y
FUSE
C O R D T O
1 1 0 A C S O U R C E
Fig. 23— Vacuum Pu mp
• 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. 23).
Recharge with 8 ounces of vacuum pump oil, Frigidaire
150 or equivalent (fig. 23). If you desire to flush out the
pump, use the same type clean oil. Do not use solvent.
Improper lubrication will shorten pump
NOTE:
life.
• If this pump is subjected to extreme or prolonged
cold, allow it to remain indoors until oil has reached
approximate room temperature.
oil will result in a blown fuse.
P U M P P U M P D IS C H A R G E
INLET OUTLET
Failure to warm
10-30 CHEVROLET TRUCK SERVICE MANUAL