Chevrolet Light Duty Truck 1973 Service Manual page 97

pressor damage due to a loss of refrigerant charge is prevented.
The cause of the refrigerant loss must be corrected
system charged prior to replacing the thermal fuse. The super­
heat switch does not have to be replaced when it cycles and is
reusable unless it is determined that the switch is faulty.
Superheat Switch (Fig. 82)
The switch diaphragm and sensing tube assembly is
charged with R -114 refrigerant and the sensing tube
protrudes into the suction cavity of the rear compressor
head to sense suction gas temperatures. The internal
pressure of the diaphragm and sensing tube assembly is
affected thermally by the suction gas temperature and
the diaphragm affected externally by the suction
pressure.
The electrical contact welded to the diaphragm will only
contact the terminal pin during a low pressure-high
temperature condition. High pressure-high temperature
or low pressure-low temperature conditions will not cause
the contacts to close. The contacts may be either "open"
or "closed" in a Tolerance Zone depending on the
characteristics of the switch and accuracy of pressure and
temperature readings taken.
Replacement
1. Completely discharge the air conditioning system.
2. After the system is discharged, remove the
superheat switch retainer ring, using J-5403 Internal
Snap Ring Pliers (fig. 83).
3. Remove superheat switch from the rear head by
ELECTRICAL
C O N T A C T
D IAP H R AG M
M TG . BASE
BASE
O P E N IN G S (4)
Fig. 82-Superheat Switch Schematic
and the
TERMINAL
H O U S IN G
D IA P H R A G M
ASSEMBLY
S E N S IN G
TUBE
10. Evacuate, charge and check system operation.
Thermal Fuse (Fig. 85)
The thermal fuse consists of a temperature sensitive fuse
HEATER A N D AIR C O N D IT IO N IN G
Fig. 83--Superheat Switch Removal
pulling at the terminal housing groove with J-9393
or a pair of screwdrivers.
4. Remove "O " ring from the switch cavity in the rear
head. Use "O " ring removal Tool J-9553.
5. Recheck superheat switch for closed contacts. See
Superheat Switch Check in Service Diagnosis Table.
Replace as necessary.
6. Check the superheat switch cavity and "O " ring
groove in the rear head for dirt or foreign material
and be sure area is clean before installing the "O "
ring. Install a new "O " ring in the groove of the
superheat switch cavity in the rear head. Lubricate
the "O " ring liberally with new refrigeration oil
before installing.
7. Lubricate housing of the superheat switch with new
refrigeration oil, and insert switch carefully into
switch cavity until switch bottoms. J-9393 may also
be used to install the switch.
8. Using J-5403 Internal Snap Ring Pliers, install
superheat switch retaining ring with high point of
the curved sides adjacent to the switch housing. Be
sure retainer ring is properly seated in the snap
ring groove.
9. Check for electrical continuity between the switch
terminal and switch housing to be sure the contacts
are open according to the Calibration Chart (fig.
84).
1A-71
LIGHT DUTY TRUCK SERVICE MANUAL