I have know idea. I know I ran the same setup with 2 6548's and not once did the AC not start for 2 summers. When I first installed this inverter it shut down trying to start AC. Now after numerous firmware changes it will run AC.I will have someone contact you for a RMA. I want to personally test your inverter when it comes in as well I can post the results here if you are ok with that. After you get a new replacement and this problems is still going on what would you suggest the problem is at that point?