I had my aircon recharged in March 2008 and it lasted a year. I had it recharged again this March and it's stopped working again, so I only got about 3 months this time.

I was told (by Kwik Fit) that their machine would only charge up a system that passed certain tests. Can anyone with any experience of this advise how I should proceed? Should I ask them to perform more diagnostic checks or should I bite the bullet and take it to a dealership and empty my wallet?

Many thanks.

First check should be that you haven't got a hole in any of the components in the system (a form of pressure test)