GMC 1994 Yukon Owner's Manual page 148

Rear Air Conditioning and Rear Heater
If your vehicle has a rear air conditioning and rear heater system
combination, controls are provided to regulate the temperature, location and
speed of the air flow.
Front Control
1
. . .
,
Rear Control
To adjust the air temperature, turn the temperature knob on the right side of
the control panel. For warmer air, turn the knob to the right (red) side, and
for cooler air, turn the knob to the left (blue) side.
To regulate the air flow location, adjust the center knob on the control panel.
Turn the knob toward the left for floor vent air flow or toward the right for
headliner vent air flow. Generally, the upper vents are used for air
conditioning and the floor vents for heating: However, the control knob may
be set to allow any desired blend of air flow.
To adjust the air flow speed, turn the fan control knob on the left side of the
control panel to the desired blower setting.
To activate the rear control, move the fan knob on the front control to
REAR CNTL. This will allow second seat passengers to adjust the controls
as they desire.
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