knocking sound

i have lancer 2004 there is a prob that it produces sound of knocking what is the prob and what is the solution of this prob
..
sound of knocking is increased when a/c is switched ON/

I thought you mena an 2004 Lancer EVO. then i would say run 93 octane, but since you arent turbocharged...idk

i am in pakistan the octane rate is very low
i have simple lancer GLX 1300cc
tell me the solution of this problem

THANKs