A/c does not work in my Peugeot 306 Vivante?

I have a peugeot 306 vivante 1998 1400 R reg. My A/C wont work even though the light comes on. It has not run for awhile so I guess the refrigirant level is low. What I would like to know as well is where the relay for the A/C is located & what other checks I need to make to ensure that I can establish the cause of the non-function of the unit. All fuses seem to be in order & it does seem that the fans are all working. All possible info will be welcomed. Thank u