1995 GMC Yukon Owner's Manual - Page 166

To increase and decrease the flow of heated air to the rear floor vents, move the switch marked REAR HEAT to the blower speed you want. The knob has three speed positions. To increase the flow of heated air, move the switch toward HIGH. To decrease the flow of heated air, move it toward LOW. To turn the fan off, move the switch to OFF. 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. To adjust the air temperature. turn the temperature knob on the right side of the control panel. For warmer air, turn the knob clockwise toward the red side, and for cooler air, turn the knob counterclockwise toward the blue side. To regulate the air flow location, adjust the center knob on the control panel. Turn the knob counterclockwise for floor vent air flow or clockwisefor headliner vent air flow. Generally, the upper vents are used for air conditioning and the floor vents for heating. The control knob can be set to any blend setting. 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. 3-6