GMC 1982 Light Duty Truck Service Manual page 57

IB - 14 AIR CONDITIONING
ELECTRICAL/VACUUM TROUBLE DIAGNOSIS
W hen 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.
O p eratio n al Test
To aid in determ in in g w hether or not the air
conditioning electrical, air, vacuum and refrigeration
systems are operating properly and efficiently, refer to Chart
1B 3
C-K and G , C 6 0 SYSTEM
S ta rt 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 (Refer to 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 T han N orm al 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 N orm al 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 p ertinent vacuum
actuators. If vacuum exists at the actuator but the door
does not move, 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.
V A C U U M SYSTEM
Operation of the air conditioning blower at all four
i .
speeds and engagement of the compressor clutch would
indicate th a t electrical circuits are
properly.
2. The same hand-felt tem perature of the evaporator inlet
pipe and the accumulator can surface of an operating
system would indicate a properly charged R - 12 system.
3. Operation of the A /C control selector (mode) lever to
d istribute air from designed outlets would indicate
proper vacuum and diaphragm function.
DIAGNOSIS
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 A N D W IR IN G D IA G R A M S
Refer to Fig. 1B-14 thru 1 B-22.
A /C REFRIGERANT SYSTEM
DIAGNOSIS
INSUFFICIENT C O O L IN G "Q U IC K -C H E C K "
PROCEDURE
The following C C O T "H a n d -F ee l" procedure can be
used to quickly determine whether or not the A /C system
has the proper charge of R efrigerant-12 (providing ambient
temperature is above 21°C (70°F) This check can be made
in a matter of minutes, simplifying system diagnosis by
pinpointing the problem to the am ount of Refrigerant-12
charge in the system or by eliminating this possibility from
the over-all checkout.
1. Engine m ust be w arm ( C H O K E O P E N and O F F
FA ST ID LE SP E E D C A M ) and at normal idle speed.
2. Hood and body doors open.
3. Selector (mode) lever set at N O R M .
4. Temperature lever at COLD.
5. Blower on HI.
6. " H a n d - F e e l" te m p e ra tu re of evaporator inlet pipe
after orifice and a c c u m ulator can surface with
compressor engaged.
a. B O TH S A M E T E M P E R A T U R E AND S O M E
D E G R E E C O O L E R T H A N AM BI E N T - P r o p e r
condition: check for other problems (Refer to A /C
System Diagnostic Procedure).
b. IN L E T PIPE C O O L E R than accumulator surface
low refrigerant charge.
• Add slight amounts 120 ml (1 /4 lb.) of refrigerant
U N T IL BOTH feel the same temperature. Allow
stabilization time between additions.
• Then add 420 ml (.88 lbs.) one can additional
refrigerant. (The 420 m l / 14 oz. disposable can of
Refrigerant-12 is the equivalent to .88 lbs.)
c. IN L E T PIPE HAS F R O S T A C C U M U L A T IO N -
Accumulator surface warmer; proceed as in Step b
above.
functioning