Chevrolet 1979 Light Duty Truck Owner's Manual page 59

Since refrigerant is controlled by the Four Season System, the only
control provided: on the rear overhead system is a three speed blower
switch on the instrument panel.
In the OFF position, the blower is inoperative, even though the
refrigerant is circulating in the system if the front system is ON. To
operate the rear overhead system, simply select the desired blower
speed (LOW, MED, HI).
NOTICE: The rear blowers may be used to simply circulate interior air
regardless of front system operation.
Air Conditioning Operating Tips
Close all windows and vents when operating air conditioner except for
the first few minutes of operation when the vehicle interior is very hot.
Close all windows as soon as the excessively heated air has escaped.
RADIOS
Your vehicle may have one of several optional GM Delco Sound
Systems. Although a wide variety of features is offered, the following
basic controls are common to all systems.
Controls-All Radios
•
Left Knob - This knob turns the set on or off, and controls the
volume. (To use the radio, the ignition must be in "Run" or
"Accessory" position.) Behind the volume knob is a tone control.
When turned to the right, it increases treble and voice clarity;
when turned to the left, it increases bass.
•
Right Knob - This knob is a manual tuning control for choosing
radio stations. For radios with rear speakers, a fader control is
located behind it. This control adjusts the sound between the front
and rear speakers.
•
Pushbutton& - Each radio has five pushbuttons you can use to
select your favorite stations. After using the pushbuttons you may
have to "fine-tune" the radio by hand for the best reception.
To "set up" the pushbuttons:
Manually tune to the desired station.
1 .
Choose the button you wish to use. Pull it straight out, then push
2.
it back in firmly until it stops.
Do this for each of the five buttons.
3.
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