On my53 blob wrx I never use the aircon but have started useing it the odd times and not really seen any less fuel used when on or off. What it is im getting when the engine is warming up and aircon is on when the fan is on also the engine pops at 2000rpm and can do it on occasional driveing. I do have a problem with my sti uppipe leaking somewhere behind the heat shield as its showing black sut