This is the first time since I have been here that I have heard of this happening. As you probably already know, the blinking ECC display is the programmer telling you that it sees an issue. So, your saying that you can get cold air by selecting 90* (or max) and the air stays cold for a long drive?
Unless something is hooked up backwards, I would think it it would have to be the programmer, since it provides the inputs that drive the temp as well as air discharge locations utilized. Default (if the system fails) is hot air from the floor vents and defrost.
This issue is totally baffling.