1997 GMC Safari Owner's Manual - Page 151

Rear Air Conditioning System (Option) Air Conditioning Before using your vehicle's air conditioning,open the of windows to clear the vehicle hot air. This reduces the time it takes for your vehicle to cool down. Then keep your windows closed for the air conditionerto work at its best. You can use MAX A/C with the temperature knob in the blue area when it's really hot outside and you need to cool the inside airquickly. MAX A/C lets in only a little air from the outside. If you first use MAX A/C, you can then use A/C with the temperature knob in the blue area, as soon as the vehicle has cooled down, so outside airwill be going through your vehicle. You may have rear air conditioning. The air rear conditioning switchis located to the right of the heater controls. Turn the switch toward HIGH for higher airflow in the rear area. Turn the switch to the OFF position to turn the system off.