Choice Home Warranty Refused to replace an AC. Edison New Jersey

 CHW refused to replace a failed AC unit.   We were told that our AC had a "pre-existing" condition.  Apparently there was a valve that was added to the outside unit that would "Sooner or Later" cause the unit to break down and need to be replaced.  This valve was added before he bought the house in 2008.  We purchased a Home warranty from Choice in June 2012 and our unit was in perfect working order at that time. 

We did not have a claim for that unit for 11.5 months after we purchased the warranty.  We were told that was not covered and we should have been known there was something  different on the unit even though neither of us know anythign about AC's and was told that is a buyer beware situation.  Isn't that why you purchase a warranty, to cover something when it breaks down????