2006 Winnebago Outlook / E450 Cab AC issue

This may have nothing to do with your issue, but I always thought the difference between normal AC and max AC was that normal AC is cooling fresh, hot outside air coming in to the cabin vs. cooler, recirculated air from inside the cabin.

Perhaps one of the air flow dampers under the dash is stuck in a closed or partially open or fully open position that it shouldn't be in.