Likely a blend door not closing or opening fully when in the NORM position.
These doors are controlled by vacuum diaphragms under the dashboard. A vacuum line comes into it on the passenger side of the dashboard, goes to a junction and is then distributed to various vacuum operated devices/diaphragm. Check the operation of these devices. Seems that one isn't opening or closing the door completely.
Thursday, June 20th, 2013 AT 5:57 AM