1998 GMC Suburban Owner's Manual - Page 168

Generally, the upper vents are used for airconditioning and the floor vents for heating. The control knob can be set to any blend setting. Air Conditioning On hot days, open the windows long enough to let hot air inside escape. This reduces the time it takes for your vehicle to cooldown. Then keepyour windows closed for the air conditioner to work its best. The recirculation button, between the fan and temperature knobs, allows the air inside your vehicle to be recirculated. This setting helps to maximize your air conditioner's performance and your vehicle's fuel economy. This setting also cools the air the fastest and can be used to keepunwanted odors and/or dust from entering the vehicle. When using the air conditioner, turn off recirculation after the vehicle reaches a comfortable interior temperature. When the right knob on the control panel is between HEATER and DEFROST, the recirculation feature will not function. The A/C button, between the temperature and mode knobs, allows the air coming intoyour vehicle to be cooled. This setting is useful for normal cooling on hot days. When you use A/C with the recirculation button pushed in, turn off recirculation as soon as the vehicle reaches a comfortable interior temperature. To adjust the air temperature, turn the temperature knob on the right of the control panel. For warmer air, turn the knob to the right toward the red, and for cooler air, turn the knob tothe left. The rear control works just like the front control. It will allow second seatpassengers to adjustthe controls as they desire. 3-6