Well, what is missing? Did they just take the compressor or is there a large, gaping hole in the firewall where the A/C suitcase used to be? I would go to the junkyard and find a car with the same engine family as yours and see how it was set up. A basic A/C system consists of a compressor, receiver/dryer, condenser, evaporator core, a cycling switch, hoses, an orifice tube, and a fan to blow over the evaporator core and cool the car. I will be doing an A/C install in my car in about a month and will detail it in my build thread when it happens if you want to follow along. My car uses a hybrid system made up of Camaro V8 and Cutlass V6 parts.