Legal Question in Real Estate Law in California

I'd say probably not; I don't know of any actual decisions on the issue of wrong-sizing air conditioning units, but even assuming it could be proven to the court's satisfaction that 6 tons total a/c capacity was inadequate for a 4380 sq.ft. house in Oakley, I'm doubtful that there's an obligation on the builder to provide any particular amount of cooling capacity. Maybe the builder intended to keep the interior below 75, and you tried to keep it at 70, or something like that. Also, the failure of the a/c unit isn't necessarily because it's undersized ..... perhaps it failed for some completely independent reason, notwithstanding that it's also true that it was undersized.