2003 Subaru Impreza Owner's Manual - Page 176

Climate control Air filtration system (if equipped) If your vehicle's air conditioning system is equipped with an air filtration system, replace the filter element according to the replacement schedule shown below. This schedule should be followed to maintain the filter's dust collection ability. Under extremely dusty conditions, the filter should be replaced more frequently. It is recommended that you have your filter checked or replaced by your SUBARU dealer. For replacement, use only a genuine SUBARU air filter kit. Replacement schedule: Every 12 months or 7,500 miles (12,000 km) whichever comes first NOTE The filter can influence the air conditioning, heating and defroster performance if not properly maintained. - CONTINUED - 4-13