Chevrolet Light Duty Truck 1973 Service Manual page 65

Fig. 43--Floor and Overhead Controls (G Models)
temperature knob and a three speed blower switch. The
controls are mounted on the blower-evaporator cover to
the right of the driver (fig. 43).
The temperature knob is used to control the degree of
cooling desired. Fully clockwise at CITY provides
maximum cooling while turning the knob to HIWAY
provides adequate cooling for highway operation.
The three speed blower fan switch (LOW-MED-HI) is
used to control the quantity of air flow.
NOTE: Reduced cooling and freezing of the
evaporator could be encountered when
operating at highway speeds with the controls
at the "CITY" setting.
Overhead System (G Models)
This system operates in conjunction with the front floor
mounted system. Since refrigerant is controlled by the
front system the only control provided on the rear
overhead system in a three speed blower switch (fig. 43).
In the OFF position, the blower is inoperative; however,
In any vocation or trade, there are established
procedures and practices that have been developed after
many years of experience. In addition, occupational
hazards may be present that require the observation of
certain precautions or use of special tools and
equipment. Observing the procedures, practices and
precautions of servicing refrigeration equipment will
greatly reduce the possibilities of damage to the
customers' equipment as well as virtually eliminate the
element of hazard to the serviceman.
PRECAUTIONS IN HANDLING
REFRIGERANT-12
Refrigerant-12 is transparent and colorless in both the
gaseous and liquid state. It has a boiling point of 21.7°F
below zero and, therefore, at all normal temperatures
refrigerant is circulating in the system if the front system
in ON. To operate the rear overhead system, simply
select the desired blower speed (LOW, MED, HI).
Dash Mounted Unit (Motor Home Chassis
Units)
This system is self contained and is mounted below the
dash by the body manufacturer. System controls consist
of an AIR knob and TEMP knob located in the center of
the unit face plate (fig. 44).
Air Knob
Turning the AIR knob clockwise operates a three speed
(LOW-MED-HI) blower motor.
Temp Knob
This knob is used to control the degree of cooling
desired. Fully clockwise at CITY provides maximum
cooling, while turning the knob to HIWAY provides
adequate cooling for highway operation.
GENERAL IN FO R M A TIO N
and pressures it will be a vapor. The vapor is heavier
than air, and is noninflammable, nonexplosive, nonpoi-
sonous (except when in contact with an open flame) and
noncorrosive (except when in contact with water).
HEATER A N D AIR C O N D IT IO N IN G
Fig. 44- Motor Home Unit Control
NOTE: The rear unit will not operate unless
the front unit is calling for cooling.
NOTE: Reduced cooling could be encoun­
tered when operating at highway speeds with
the controls at the CITY setting. The heater
must be fully off to obtain maximum cooling.
The following precautions in
WARNING:
handling R-12 should be observed at all
times.
• If it is ever necessary to transport or carry a cylinder
or can of refrigerant in a car, keep it in the luggage
compartment. Refrigerant should not be exposed to
the radiant heat from the sun since the resulting
increase in pressure may cause the safety valve to
release or the cylinder or can to burst.
1A-39
LIGHT DUTY TRUCK SERVICE MANUAL