I'd check the two vacuum pods behind the glove box. It's not too difficult. Remove the glove box liner (5 or 6 little push pins) and unplug the glove box light. Almost sounds like one/both of these pods may be defaulting to "fresh air in".
A search will reveal a more comprehensive method of glove box removal, but you get the idea.
May not be this, but it's so easy to check.
I second wbain's recommendation for Pindelski.com for these types of 126 problems. It is very good. Best $30 you'll spend on repair/maintainance. FWIW