A/c Vacuum
 

is it true that if you put a vaccum on an a/c system that it will only hold for a while because of the design of the schrader valve? a mechanic told me he could put a vacuum on my car but he didnt have a way of putting my r12 cans in. convieniently. he said if i pulled a vaccum and didnt recharge within an hour i would lose the vaccum.

You have to leave the hoses attached. Why would you pull a vacuum, remove the hoses and then reattach the hoses and recharge, anyway?

If you put the caps back on it should hold a vacuum for a while.

There's a little adapter that will attach his hose to your can. Get one of those.

Yeah, it does not make any sense to disconnect the hoses and reconnect it later. When you will try to reconnect, air will get in, and you do not want to put expensive R12 with air already in it. You have to use proper tools, like a pressure gauge and proper hoses to be able to vaccum and charge the unit properly, it does not seem like this is the right mechanic if he does not have these tools. R12 is very expensive so dont charge the system using this reconnect-disconnect method, go to an auto air shop.