Vac lines for Ac/heater control

[WorkingOnItStill]

I have a quick question that I hope some one can answer. My vac lines going to the control panel are all connected only thing is, I have nothing that looks like a vac line coming in to the engine bay. What line provides the suction and where should it exit in to the engine bay? All the interior lines look like they are hooked up to the heater box.
Its a 73 factory a/c that has been removed long ago
Thanks for all the help, Charles   

[Chryco Psycho]

the line enters the engine bay through a hole in the firewall under the heater hose connection , I think the other end connects to the switch plug

[WorkingOnItStill]

Thanks I will have a look after it cools down tonight !