My wife's 99 V70 has a leak in the evaporator so I have been adding r134 when it needed it. It's about $1100 to fix, so I just refill it. Whenever it quits cooling, I add a couple of 12 oz. cans. I recently bought a manifold gauge set and a 30lb can of r134 ($79 at Autozone, but I heard Sam's Club has it for less than $70.), but don't know how to go about putting in the proper amount. The instructions tell how to check the static and dynamic pressure, but not how to properly charge the system. Please pass on any advice or where to look for this information. As always, thanks in advance.