GMC 1976 ZEO 6083 Maintenance Manual page 76

NOTE : It will be necessary to close bleed valve
periodically to allow boiling to subside to check
level in the sight glass of Charging Station cylin-
der.
b. Bleed cylinder valve on top (behind control
panel) as required to allow refrigerant to enter. When
refrigerant
reaches desired level (see "System
Capacity"), close valve at bottom of cylinder and be
certain bleed valve is closed securely .
2 . Continue to evacuate for remainder of 10 mi-
nute period .
3 . Turn hand shut-off valves at low and high
pressure gauges of gauge set to full clockwise posi-
tion with vacuum pump operating, then stop pump .
Carefully check low pressure gauge for approxi-
mately two minutes to see that vacuum remains con-
stant . If vacuum reduces, it indicates a leak in the
system or gauge connections; locate and repair all
leaks.
CHARGING THE SYSTEM
1 . Only after evacuating as above, is system ready
for charging . Note reading on sight glass of charging
cylinder . If it does not contain a sufficient amount of
refrigerant for a full charge, fill to the proper level.
2. With High and Low Pressure Valves open,
close Vacuum Control Valve, turn off vacuum pump,
open refrigerant control valve and allow refrigerant
to enter system .
NOTE: If the charge will not transfer completely
from the station to the system, close the high
pressure valve at the gauge set, set the air condi-
tioning controls for cooling, check that the en-
gine compartment is clear of obstructions, and
start the engine . Compressor operation will de-
crease the low side pressure in the system .
System is now charged and should be checked as
outlined below:
CHECKING SYSTEM OPERATION
1 . Operate system for a maximum of five minutes
at maximum cooling, high blower speed and with
engine operating at 2000 RPM (exhaust should be
vented if inside) .
2. When system is stabilized, the pressure gauges
on the charging station should read pressures corre-
sponding to values listed under PERFORMANCE
DATA .
3. When correct system pressures are observed,
check system charge as described under "Refrigerant
AIR CONDITIONING SYSTEM 1- 59
Quick Check Procedure" .
4. Feel outlet air distribution to ensure that cold
air is being distributed .
5 . Disconnect gauge lines and cap fittings .
CAUTION : When removing gauge lines from
fittings, be sure to remove the adapters from
the fittings rather than the gauge lines from
the adapters.
PERFORMANCE TEST
Under normal circumstances, it will not be neces-
sary to Performance Test a system as outlined below;
however, in certain instances, the following proce
dure may be advantageous in diagnosing system mal-
function .
NOTE: The following performance test and data
do not apply to vehicles equipped with the addi-
tional air conditioning outlets shown in Figure
25 .
The following fixed conditions must be adhered
to in order to make it possible to compare the per-
formance of the system being tested with the stand-
ards below :
1 . Windows and curtains open . (Vehicle inside or
in shade) .
2 . Vehicle in NEUTRAL with engine running at
2000 rpm.
3 . Air Conditioning controls set for -
. Upper control on A/C.
. Lower control on cold .
High blower speed .
4. Disconnect temperature sensor on engine cool-
ing fan.
5. Gauge set installed.
6. System settled out (run-in approximately 10
minutes) .
7. A thermometer placed in front of vehicle grille
and another in the center diffuser outlet .
NOTE: Higher temperatures and pressures will
occur at higher ambient temperatures. In areas