Chevrolet 70 1969 Series, Shop Manual

Page: 95 / 913

CAB
A N D B O D Y M O U N T IN G S 1-68
Testing to determine if the discharge air temp­
erature, suction pressure, and discharge pressure
meet the specifications at a particular ambient
condition is called a "Performance Test."
The suction throttling valve is pre-set at the
factory to maintain the minimum and maximum
evaporator core pressure and generally should
never require resetting. If a malfunction in the re­
frigerant system due to above or below normal
evaporator core pressures is suspected, check the
following:
1. Restrictions in evaporator core, hoses,
tubes, etc,
2. Refrigerant leaks.
3. Compressor clutch slippage.
4. Improper drive belt tension.
5. Capillary tube broken or not tight to evap­
orator tube.
6. Expansion valve inoperative.
7. Suction throttling valve stuck.
The purpose of performing an operational test,
is to prove that the air conditioning electrical sys­
tem, air system, and refrigeration system are
operating properly and efficiently. Results of the
test are as follows:
a. Operation of the air conditioner blower at
all speeds and engagement of the compressor clutch
would indicate that the electrical circuits are func­
tioning properly.
b. A clear sight glass would indicate a properly
charged refrigeration system.
e. Proper evaporator pressure, as controlled
by the Suction Throttling Valve would provide prop­
er "freeze protection" for the evaporator,
d. Proper nozzle temperatures would indicate
a system free from warm air leaks.
Check and correct all air and refrigerant leaks
in the air conditioning system as well as operation
of cable-operated air doors.
Check for proper compressor oil level during
the repair of refrigerant leaks, before conducting
an operational test.
P R E L IM IN A R Y C H E C K S
1. Check compressor belt for proper tension;
if below 100 lbs. (used belt) adjust to 100-105 lbs.
using belt tension gauge.
2. Check all refrigeration lines for leaks,
kinks, or other restrictions.
3. Check outer surfaces of radiator and con­
denser cores to be sure they are not plugged with
dirt, leaves or other foreign material. Be sure to
check between the condenser and radiator as well
as the outer surfaces.
4. Connect engine tachometer,.
5. Start engine and operate at 2000 rpm with
"A I R " lever on "O U T S I D E " and " T E M P " lever set
for maximum cooling, and blower on high. After at
least five minutes of engine operation,, observe for
Figure
12— -Gouge Hose
Connection
at Suction Throttling Valve
bubbling at the sight glass (above 7 0 °F . ambient).
If the system is low on refrigerant, add refriger­
ant until liquid indicator just shows clear and add
an additional 1 / 2-pound of refrigerant.
6. Under the same conditions as in step 5
above, move "A IR C O M 3 " lever to " O F F . " This
should disengage the compressor clutch. If clutch
does not disengage, check the clutch control switch
adjustment.
7. Move "A IR C O N D " lever to " O N " again and
observe clutch engagement action which should be
without slip. If clutch slips, check clutch for proper
adjustment, short in clutch coil, or leaking com­
pressor shaft seal.
8. Change blower speed to medium, and to
low, and observe for decreases in air flow.
F U N C T IO N A L T E S T
N O T E : This test should not be performed in
direct rays of sun,
1. Connect gauge set high pressure hose to
outer gauge fitting at rear of compressor and con­
nect 30-inch vacuum, 60-psi compound test gauge
hose to refrigerant fitting at suction throttling
valve (fig. 12).
2. Locate auxiliary fan (at least 20" in diam­
eter) in front of condenser. Leave hood open.
3. Open both cab doors.
4. Place a calibrated thermometer in front of
condenser
in
auxiliary fan air stream.
5. Place a second calibrated thermometer in
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M A N U A L