runs really bad with the A/C on

My problem is when I go crank my car then start going,then turn the A/C unit on the car just runs bad. when I go to mash gas, it spark knocks real bad. going up a hill is almost in possible, the car bogs down has no power, and continues to spark knock every time the gas is mashed. have to mash gas almost to floor just to try in get up a hill, or start off at a light.