A/C Compressor Won't Kick On

The canister looks to be a vaccum canister. The way I would think that the lines should go is one vaccume line to a vaccum sorce and the other to the vaccum controls for the A/C. I'm not sure where the second vaccum hose would go from the firewall unless there is another vaccum dashpot somewhere. Bear in mind that I'm talking on what it looks like. I may be totally off base.