Mike,
I know that this is a dumb question and others may have asked it and I just missed it reading the posts, but does the defroster work? I am not familiar with your cars setup, but in mine the core is inside the car and the defroster gets its heat from the core and it is just changed from heat to defrost with a slider which physically opens and closes a door in the duct work under the dash. If the defroster works, then I would suspect you have a door in the duct work not opening or closing. I am sure this has already been covered in previous posts, but getting to anything in my car under the dash is a real pain in the A**.
Ron