every week otherwise the rubber seals will perish and the gasses will escape,
no gas, no air con. Use it or lose it.
OK, I Lost It, What Now?
You have 2 options, DIY or get a professional to do it.
420g + 0mg is the figure I have been told but 0mg of oil must be a refill
measurement assuming that the gas has escaped and the oil is still in the system.
Get a Professional
Look online for a local garage that deals with AC. This way you know
the system has been drained and everything has been done properly.
Do It Yourself
The Government in many countries have banned the sale of disposible R134A canisters.
There are other compatible replacements and companies claiming it's not R134A when it actually is.
You will have to look around and see what you can get.
Remove the front panels
the bonnet panel off but the tubes you get with the DIY kits are too short (Thanks Bob S).
With the panels removed, look into the left hand side hole.