Deffinately replace your Cabin Air Filter. Let's see......the AC Delco filter number is a CF104.....and a stopped up cabin filter will also make your AC bow warm air when you turn it on....and you can loose some heater pressure.

You might also buy a can of Evaporater/AC system de-odorizer...the GM part # is 12377952. It will destroy the bad smells left in your duct work that's caused by diffrent depostis like dust from a DIRTY CABIN FILTER, micro drops of coolant or freon and bacteria's that grow on the plastic due to condensation. Trust me..it works...!

 

this happened to my old ford, bad heater core, see if the air is slightly moist.

 

I dont believe the 04's have a changable filter do they? I have never changed mine.
Torque_Wrench.. Any input on this?

 

I think that they stopped using the cabin filters after 02...

 

Thats what I though but I wasn't sure.

 

Yep, no applications after the 2003 and up model years in the trucks. Got all kinds in the cars.

 

Yeah I wish I had cabins in mine. I used to work at a fast lube type place and those things catch so much junk.