Chevrolet 10 Series 1968, Service Manual

Page: 49 / 713

HEATER AND AIR CONDITIONING 1A-18
7. Check the system controls for proper operation.
6000 MILE INSPECTION
1. Check unit for any indication of a refrigerant leak.
2. If there is an indication of an oil leak, check the
compressor for proper oil charge.
3. Check sight glass for proper charge of R efriger­
ant-12.
4. Tighten the compressor brace and support bolts and
check the belt tension.
5. Check hose clamp connections as in Step 5 above.
PERIODIC SERVICE
® Inspect condenser regularly to be sure that the fins
are not plugged with leaves or other foreign material.
• Check evaporator drain tubes regularly for dirt or
restrictions.
• At least once a year, check the system for proper
refrigerant charge and the flexible hoses for brittle­
ness, wear or leaks.
• Every 6000 miles check sight glass for low refrig­
erant level.
• Check belt tension regularly.
INSTALLING CHARGING STATION TO CHECK
SYSTEM OPERATION
The Four-season System high pressure gauge connec­
tion is located on the muffler. The low pressure con­
nection is located on the P.O.A. valve.
1. Install Gauge Adapter (J-5420 or J-9459) onto the
high and low pressure gauge lines.
2. With the engine stopped, remove the caps from the
cored valve gauge connector on the compressor
connector block and P.O.A. valve.
3. Be certain all valves on charging station are closed.
4. Connect high pressure gauge line to high pressure
gauge fitting.
CA U TIO N :
When removing gauge lines from
the compressor fittings block be sure to remove
the adapters from the fittings rather than the
gauge lines from the adapters.
5. See Figure 27. Turn high pressure control (2) one
turn counter-clockwise (open). Crack open low pres­
sure control (1) and allow refrigerant gas to hiss
from low pressure gauge line for three seconds,
then connect low pressure gauge line to low pressure
gauge fitting.
6. System is now ready for performance testing.
PERFORMANCE TEST
This test may be conducted to determine if the system
is performing in a satisfactory manner and should be
used as a guide by the serviceman in diagnosing trouble
within the system. The following fixed conditions must be
adhered to in order to make it possible to compare the
performance of the system being tested with the stand­
ards below:
1. Doors and windows closed. (Vehicle inside or in
shade.)
2. Hood up and engine exhaust suitably ventilated.
3. Vehicle in NEUTRAL with engine running at 2000
rpm.
4. A ir Conditioning controls set for -
• Maximum cooling.
• High blower speed.
5. TEMPERATURE knob set at maximum cold and AIR
knob set for “ Inside A ir ” .
6. Gauge set installed.
7. System settled out (run-in approximately 10 minutes).
8. A thermometer placed in front of vehicle grille and
another in the right hand dash outlet.
PERFORMANCE DATA
The following Performance Data define normal opera­
tion of the system under the above conditions. Relative
humidity does not appear in the tables because after
running the prescribed length of time on recirculated air
and maximum cooling, the relative humidity of the air
passing over the evaporator core will remain at ap­
proximately 35% to 40% regardless of the ambient tem­
perature or humidity.
Should excessive head pressures be encountered at
higher ambient temperatures, an 18" fan placed in front
of the vehicle and blowing into the condenser will provide
the extra circulation of air needed to bring the pressures
to within the limits specified.
NOTE:
Higher temperatures and pressures
will occur at higher ambient temperatures. In
areas of high humidity it is possible to have
thermometer and gauge readings approach but
not reach the figures listed in the performance
tables and still have a satisfactory operating
unit. However, it is important to remember that
low pressure has a direct relationship to nozzle
outlet temperature. If pressure is too low, ice
will gradually form on the evaporator fins, re­
stricting airflow into the passenger area and
resulting in insufficient or no cooling.
(Refrigerant Charge = 3 Lbs. - 4 Oz.)
Temperature of
A ir Entering
70 80° 90° 100° 110°
120u
Condenser
Engine rpm
2000
Compressor Head
145- 185- 200- 215- 255- 285-
Pressure
155 195 210 225 265
295
Evaporator Pressure
Dependent Upon Altitude
at POA See Chart Under Evaporator Con­
trol Valve (POA)
Discharge A ir 38
38- 40- 41- 43- 48-
Temp, at Right
41 41 43 44 46
51
Hand Outlet
EVAPORATOR CONTROL VALVE (POA) (Fig. 30)
The only check for proper POA valve operation is to
check the suction pressure at the valve during a per­
formance test. The POA valve is an absolute valve and
will provide different gauge readings based on the alti­
tude where the readings are being taken. Correct gauge
reading at sea level is 29.5 psig. Gauge readings will
be one-half psi higher for each additional 1000 feet of
elevation. The following table lists gauge readings at
CHEVROLET TRUCK SERVICE MANUAL