Sounds like you both would breach the lease if you were to vacate early.  If you feel the landlord failed to provide habitable premises you should have left then. Not later on after the fact.  That would be like saying it is ok that you had to suffer without a/c.  If that is the only thing the landlord failed to provide you might lose this fight as he did repair it it a fairly reasonable time.  Summer is the busiest time for repair techs and cannot always schedule service on demand. Sometimes it takes an appointment to schedule a/c repair that means being put on a waiting list.  Sorry but I don't think that is sufficient reason to break lease.  Good luck.