GMC 1995 Suburban Owner's Manual page 165

To operate the rear air conditioning system, the front air conditioning
system must be on. With the front air conditioning system off, the rear
system controls can be used
to
circulate air in the rear of the vehicle.
To operate the rear
system using the front
control, just turn the
knob to the blower
position you want.
To use the rear
control, first turn the
front control knob to
REAR CNTL. Then,
the rear control can be
used to increase and
decrease the air flow.
Rear Heater (Without Rear Air Conditioning)
If you have a rear
heater (without rear
air conditioning), the
control switch is
located on the
instrument panel.
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