Pretty sure its not the blend door. Like I said back in 2013 I had the same problem and the dealer claims they replaced the heater core which seemed to fix the problem until this year. Now the same problem. I took it in two weeks ago and they said they flushed the heater core which again appeared to of fixed the problem but this time only for a week or so. Now they claim the heater core needs to be replaced again for another $1400! My question is do you think an independent shop would be able to tell if the original core was ever replaced? I found a shop that will replace it for $650 but I want to know if the one he takes out is the original core or a replacement. If he says its original then the stealership is going to owe me $1400 from two years ago!