93 lumina vaccum canister

I have a 1993 lumina with a heating problem. The vents switch over to the defrost setting all by itself. I have a feeling that the vaccum canister under the hood has a crack in it, or is loosing vaccum for some reason or other. Does anyone know where the canister is located ? Any help would be greatly appreciated. Thank You

It's located in the fenderwell behind the battery on the driver's side.

I already found it. Thanks for your help. It was much appreciated. Thank You.