a/c wiring melting

I brought my car in for its regular maintenance  (always used dealership consistently). I was told that the a/c wiring has melted and requires $1300 worth of repairs & service.  I am the original owner - May 2012), and have had a/c questions (long time to cool, lack of adequate cooling) since the beginning and have asked the dealership service to check the a/c at least every time proceeding summer. The service rep. told me she smelled something from my car. I had passed construction two lanes over about 1/3 mile from the dealership, so I mentioned that to her because as I passed the construction, I smelled the tar and residue connected with breaking of road top and earth. She quickly came back and told me that service found that the wires had melted, but there was no reason given to why this should happen. I live in a hot desert climate and the car was last in for its maintenance less than six months ago.  My questions is what can cause the wiring to melt at (apparently) such a speed, especially since I have had my car maintained by the same dealership service and have been told the a/c is fine repeatedly.  If I get this repaired by the dealership, they provide only a one year warrantee and I don't know if the cause would still remain.  How do we find out the cause. I'm basically auto ignorant.