Chevrolet Light Duty Truck 1973, Service Manual

Page: 112 / 979

1A -86 HEATER A N D AIR C O N D I T I O N I N G
LOW R EFR IG ER A N T CHARGE PROTECTION SYSTEM
CHECK
CHECK FOR
E L E C T R IC A L
(Compressor Inoperative, Engine
Running, A/C Selector Switch “ON” ,
Thermal Fuse Disconnected).
Supply voltage at clutch coil term inals.
Blown fuse at main circuit fuse panel.
Voltage therm al fuse term inal “B” to ground. (If no voltage check
for broken lead, loose or poor connections or open am bient
switch.)
Voltage, therm al fuse term inal “C ” to ground. (If no voltage,
therm al fuse is blown. If voltage present, check therm al fuse to
clutch coil lead and connections.)
THERM AL FUSE
(Compressor Inoperative, Engine
Running. A/C Selector Switch
“O N ”, Thermal Fuse Disconnected).
Continuity betw een term inals “ B” and “ C” . (If no continuity,
fuse link is blow n, repair system and replace therm al fuse.)
Resistance, term inals “ S” to “C” to be 8.4 to 10.4 ohm.
(If not within limits, replace therm al fuse.)
SUPERH EAT SWITCH
(Engine “O F F ” , l e a d
disconnected from Superheat
Switch term inal).
Continuity betw een switch housing and ground. (If not grounded,
check continuity, switch housing to retainer ring and retainer ring
to rear head.)
Continuity between switch term inal and switch housing. (If no
continuity, contacts are open. If continuity exists, contacts are
closed.)
Install suction gauge and determine the suction pressure, determine
the approxim ate rear head tem perature and com pare conditions
noted to calibration chart. If contacts are no t open or closed
according to tem perature-pressure relations shown, discharge
system and remove switch for bench check.
SU PERHEAT SWITCH
(Switch Off Compressor)
A lternate
Closed contacts - (Housing to term inal contacts should be open
at atm ospheric pressure and tem peratures below 100°F.)
Closed contacts (with switch in a hot bath 150°F. or above).
Closed contacts (w ith sensing tube held in m atch flame for 15-20
seconds).
Note: If switch contacts are not “OPEN” or “CLOSED” per these checks, the switch is defective and must be replaced.
LIGHT DUTY TRUCK SERVICE MANUAL