I have excellent heat/airflow from all vents except nothing frim defrost vent on windshield dash. I had my windshield replaced about 6 weeks ago. Wondering if this may have caused the trouble. Only discovered the problem 2 weeks ago when the weather turned cold. Can someone help please? Frim what I have read it seems very expensive - full dash needs to come out? How can we be sure it didn’t happen when the windshield was replaced? What are our options? Thank you.