air con?

ok... i have a same explorer 100 and the air con has stoped working well i cant say that as im not sure it ever did! bougt from new. ive checked all the visable fuses and nothing so im cooking why i work! the fan works but its just hot air witch is alright some mornings! the fans on the roof that belong to the air con unit dont work so whats my problem and how do i fix it