i have a 98 e150 van. this winter the rear unit would only blow cold air, while the front would blow hot. now it is summer time and it only blows warm air (like the outside temperature)while the front blows cold a/c. it has always blown hot in the winter and cold in the summer until this past winter. it has a good volumn of air, but not blowing right temp for season. any suggestions
tks
ch