Chevrolet 1980 Light Duty Truck Service Manual page 61

ELECTRICAL/VACUUM TROUBLE DIAGNOSIS
When diagnosing problems in the electrical and
vacuum systems of the air conditioning system, consult
electrical wiring diagrams and vacuum diagrams.
Ports on rotary vacuum valves are illustrated in a
manner to provide simplicity in following vacuum
schematic lines but are numbered in consecutive order on
the actual valve.
Operational Test
To aid in determining whether or not the air
conditioning electrical, air, vacuum and refrigeration
systems are operating properly and efficiently, a table of
performance characteristics is shown in Chart IB-3.
1. Operation of the air conditioning blower at all four
speeds and engagement of the compressor clutch would
indicate that electrical circuits are functioning properly.
2. The same hand-felt temperature of the evaporator
inlet pipe AND the accumulator can surface of an operating
system would indicate a properly charged Refrigeration-12
system.
3. Operation of the A/C control selector (mode) lever
to distribute air from designed outlets would indicate proper
vacuum and diaphragm function.
VACUUM SYSTEM DIAGNOSIS
(C-K-G C 60 SYSTEM)
Start the engine and allow it to idle - move the selector
lever to each position and refer to the vacuum diagrams and
operational charts for proper airflow, air door functioning
and vacuum circuits. If air flow is not out of the proper
outlets at each selector lever position, then proceed as
follows:
1. Check for good hose connections-at the vacuum
actuators, control head valve, reservoir, tees, etc.
2. Check the vacuum source circuit as follows:
Install vacuum tee and gage (with restrictor) at the
vacuum tank outlet (see Vacuum Diagram). Idle the engine
and read the vacuum (a normal vacuum is equivalent to
manifold vacuum) at all selector lever positions.
a. Vacuum Less Than Normal At All Positions -
Remove the tee and connect the vacuum gage line
directly to the tank - read the vacuum. If still low, then the
problem lies in the feed circuit, the feed circuit to the tank
or in the tank itself. If vacuum is now normal, then the
problem lies downstream.
b. Vacuum Less Than Normal at Some Positions -
If vacuum was low at one or several of the selector lever
positions, a leak is indicated in these circuits.
c. Vacuum Normal at All Positions
If vacuum was normal and even at all positions, then
the malfunction is probably caused by improperly
connected or plugged lines or a defective vacuum valve or
valves.
3. Specific Vacuum Circuit Check
Place the selector lever in the malfunctioning position
and check for vacuum at the pertinent vacuum actuators.
If vacuum exists at the actuator but the door does not move,
AIR C O N D ITIO N IN G
then the actuator is defective or the door is mechanically
bound. If low or no vacuum exists at the actuator, then the
next step is to determine whether the cause is the vacuum
harness or the vacuum valve. Check the vacuum harness
first.
4. Vacuum Harness Circuit Check
a. Disconnect the vacuum harness at the control head.
b. The black line ( # 1 ) should show engine vacuum -
if not, trace back through connector to vacuum tank.
c. To check any individual circuit place the selector
lever at the involved circuit position and check for vacuum
presence.
V A C U U M AND W IR IN G D IA G R A M S
Refer to Figures IB-14 thru IB-22.
INSUFFICIENT COOLING "QUICK-CHECK"
PROCEDURE
The following C.C.O.T. "Hand-Feel" procedure can be
used to quickly determine whether or not the A /C system
has the proper charge of Refrigerant-12 (providing ambient
temperature is above 70°F (21°C). This check can be made
in a matter of minutes, simplifying system diagnosis by
pinpointing the problem to the amount of R-12 charge in
the system or by eliminating this possibility from the over­
all checkout.
1. Engine must be warm (CHOKE OPEN and OFF
FAST IDLE SPEED CAM).
2. Hood and body doors open.
3. Selector lever set at NORM.
4. Temperature lever at COLD.
5. Blower on HI.
6. Normal engine idle.
7. "Hand-Feel" temperature of evaporator inlet pipe
AND accumulator can surface with compressor engaged.
a. BOTH SAME TEMPERATURE AND SOME
DEGREE COOLER
condition: check for other problems (see A/C System
Diagnostic Procedure).
b. INLET PIPE COOLER than accumulator surface
low refrigerant charge.
• Add slight amounts (1/4 lbs.) of refrigerant UNTIL
BOTH feel the same temperature. Allow stabilization time
between additions.
• Then add 480 ml (14 oz.) (1 can) additional
refrigerant.
c. INLET PIPE HAS FROST ACCUMULATION-
Accumulator surface warmer; proceed as in Step b above.
Engine Idle Compensator
On V8 Engines, with factory installed air conditioning
systems, the compensator is located within the carburetor
and is accessible when the engine air cleaner is removed.
All compensators are factory set and non adjustable.
A malfunctioning unit should be replaced.
IB -1 5
THAN AMBIENT-Proper
LIG H T TR U CK S E R V IC E M ANUAL