I recently picked up an 03 Impala. I put an engine in it and now I am trying to shake out any bugs it has. When I turn the a/c on it is nice and cold coming from the passenger side vent, but when I feel the driver side vents the air is coming out, but it is warm. What gives? Is there some sort of air mix valve that is sticking? If so where would it be located? The car in question is a base model 03 Impala with a 3.4 engine. Thanks for any help.