When I have the heater going, the air coming out of the defroster & the 2 side vents is warm and toasty. The air coming out of the 2 center vents is noticeably less hot. This is using either the outside air or recirculating air position. The car sits outside, 24/7/52...maybe a creapy crawly critter made a home in there? Maybe I should try inserting a length of speaker wire, like a drain snake...