I know the thread is old but I thought i would follow up on how my warranty claim went.
No issues at all.
called conerstone before i went to a dealer to be sure the warranty was still good, and that the the dealer I was going to use was ok with them.
Made appt at dealer, let them know in advance it was conerstone warranty and they were fine with it.
Dealer checked my ac units, decided the front needed replaced, rear was fine. Conerstone approved that same day, ac ordered and installed the next morning. paid my 150 deductable and was out the door with new ac in about 24 hours.
Dealer was lazy days in tampa if that matters. I suspect it might as they are a very large dealer who does this all the time and the fact that it is sept in florida which is slow season for them prolly made it go a bit smoother.
Only thing to be aware was do not make an appt for warranty on a friday, make it for a monday morning. if you do friday you will prolly spend the weekend waiting for parts. Monday gets you out that day or the next day most every time according to the service writer we dealt with.