Recharging AC, how do I keep air out when switching cans?
 

I evacuated, drew a vacuum and am in the process of recharging my 134 AC system in my 930. I have the manifold gauges connected to the high and low ports (with the valves closed). How do I attach a can of freon (or replace a can of freon) to the yellow charge hose without introducing air into it? This air will go into the system when I open the low port gauge valve. There is no valve at the end of the charge hose to close before attaching or switching cans. As you can probably tell, this is my first time doing this.

hook the freon to the line and before opening the port valve, slightly loosen the supply line end at the manifold and allow line to purge itself. Repeat for next can

Ok, that was the only way I could figure too. One other thing I want to confirm. I was under the assumption that the valve which pierces the can top to let the freon flow will let air in even if I close it all the way down and remove the empty can. Is the purpose only to pierce the can or does it actually stop flow if you close it all the way down and remove the can. If this is the case then I wouldn't need to purge.

always purge to be sure.

when you first connect the gages, purge the lines that are connected to the system. i usually jsut crack a valve before connecting a can

I charge using the kit that comes with a low side pressure guage. Simple remove the quick connect to attach a new can.

^^ sage advice; +1