Chevrolet Light Duty Truck 1973 Service Manual page 112

1A-86 HEATER AND AIR C O N D IT IO N IN G
CHECK
E L E C T R IC A L
(Com pressor Inoperative, Engine
Running, A/C Selector Switch " O N " ,
Therm al Fuse D isconnected).
THERM AL FUSE
(Com pressor Inoperative, Engine
Running. A/C Selector Switch
" O N ", Therm al Fuse D isconnected).
SUPERH EAT SWITCH
(Engine " O F F " , l e a d
disconnected from Superheat
Sw itch term inal).
SU PERHEAT SWITCH
(Switch Off Com pressor)
Note: If switch contacts are not "OPEN" or "CLOSED" per these checks, the switch is defective and must be replaced.
LOW R EFR IG ER A N T CHARGE PROTECTION SYSTEM
Supply voltage at clutch coil term inals.
Blown fuse at m ain 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 blow n. If voltage present, check therm al fuse to
clutch coil lead and connections.)
C ontinuity 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 no t w ithin lim its, replace therm al fuse.)
C ontinuity betw een sw itch housing and ground. (If no t grounded,
check continuity, sw itch housing to retainer ring and retainer ring
to rear head.)
C ontinuity betw een sw itch term inal and sw itch 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 n o t open or closed
according to tem perature-pressure relations show n, discharge
system and rem ove switch for bench check.
Closed contacts - (Housing to term inal contacts should be open
at atm ospheric pressure and tem peratures below 1 0 0 °F.)
Closed contacts (w ith sw itch in a h o t bath 15 0°F . or above).
A lternate Closed contacts (w ith sensing tube held in m atch flam e for 15-20
seconds).
CHECK FOR
LIGHT DUTY TRUCK SERVICE MANUAL