I just bought a used 2006 Acura MDX Touring. But it seems to be stuck on Hot. It is hot all the way until you get down to Low. So if you put it on 70* it blows out hot in the front and it will blow out 70* air in the rear. Could it just be a sensor or would it be the air mix actuator? Is it an easy fix or should it be taken to the dealer?