Installing a air conditioner

I'm installing an air conditioner on a 1973 Avion Travelcader, that has never had a AC. There is a breaker in the breaker box labeled AC, and a black romax wire coming out and going into the wall. I took the front vent out, thought maybe the AC romax would be terminated there, but I'm unable to locate it. Is it terminated somewhere else that I can easily tie on to it.