As mentioned, the factory service manuals have detailed schematics for the A/C controls. There is a difference between the ’71 and ’72 systems relating to vacuum line routing to note. The ’71 system uses a vacuum actuated water valve and uses a vacuum reservoir mounted under the battery tray. The system supply line running to the reservoir and the water valve hose are the two hoses that pass though the firewall near the blower motor. Another line from the vacuum fitting at the rear of the intake manifold would run to the reservoir.
The ’72s used a cable operated water valve, has a single line firewall pass-through grommet, that supply line runs directly to the intake manifold fitting, does not have a reservoir.