i have a 1972 chevelle ss 402 with air condition. the deverter valve(the valve that blocks fluid from entering heater core) is missing and i want to install a new one. I know the vacume source goes to the control switch inside but i see no place where it was. There are no signs of anythng missing(inside around vacume switch). Does any body have a diagram where it goes and does it only close on maximum Ac.

The 1972 model does not get a water valve for the heater. That is why you have no valve and no vacuum line for it.