Question re leak
We purchased a brand new house seven years ago (2600 square feet). We shut down our A/C in September 2011 for the winter. In November 2011, we had a professional move the refrigerant line from the compressor to the furnace (we were finishing the basement). We first started the A/C in May without any cold air. We had the same conractor come out to investigate. He said that the internal coil had a leak. He said that it is typical for a builder's unit (admittedly lower quality) to break in about 7 years. He said that they no longer made parts for our unit and the type of refrigerant the unit uses is outlawed so we need to upgrade to R410A. He quoted an upgrade at $6,650.
I am suspicious of this sudden leak and wonder if it usually occurs in the internal coil within 7 years or whether moving the refrigerant line could have caused the leak. Also would like to know if $6,650 is a reasonable estimate.
Thank you, in advance, for your help.