When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
That's probably a vacuum issue. The function switch sends vacuum to the various doors to direct airflow. If there is no vacuum, the default is defrost...
The function switch is the **** you trun to select floor, vent, or defrost. On the back of that is a multi-line vacuum connector. The black line is the vacuum supply line coming from intake vacuum on a gas engine, or the vacuum pump on a diesel.