Where is the rear valve located? I have one on the firewall with two ports in and two out, and an electrical connection. Unfortunately I do not have a manual. Also when evacuating should the battery be connected or not?
PS, not trying to put all you real repair guys out, just an elderly retiree with a shade tree.

 

Technically...Freon Gas releases toxic fumes in the presence of fire. Disconnecting the battery reduces the risk of fire and therefore the risk of Toxic byproducts are reduced.....

In Realistic terms........It doesnt matter.

The rear valve is under the car, behind the right rear quarter panel. It is visible, but the rear box may need to be removed to access it.