i own a 2006 mercury grand marquis and have had to replace the a/c control unit now for the third time. every time it has failed it blows cold air but from the wrong vent. the first and time through the defrost vents only, the third through the defrost and floor vents, i am a taxi driver who uses his car daily for up to 20 hours a day, ford gives me a 12,000/1 year warranty on it which usually runs out in no time. this time just 1000 miles after the warranty ended? any suggestions?