The aircon in my series 3 au is not working.

I've looked at all the fuses none are blown.
I went over all the relays in the engine bay with a test lamp and they are all good.

When I hit the switch on the dash it doesn't light up when depressed, so I believe this is causing the aircon motor not to engage.
I also pressed the vent valve in and there was no pressure, which most likely means I've got a leak.
Does the system have a low pressure safety cut out? Hence the button not lighting up?

Anyone know of a solution or any had this sort of problem, or is it something else aswell

I'll be getting it looked at by an aircon guy in the next week but I'd just like to have some descent insight into the fault so I can tell the mechs

Cheers

Yes most a/c systems have a low/high pressure switch to shut down the system so that it doesn't get damaged .No pressure in the lines usually means no gas so nothing is going to work until the system is regassed .Due to environmental regulations the leak is supposed to get fixed before putting in gas but how do you find the leak if the gas detector can't detect the whereabouts of the leak until you gas and dye the system.Sometimes a catch 22 situation. If the dye has been put in previously then it may be spotted using a uv light and yellow tinted glasses.Kevman.