My 1990 Buick does not respond to the heater/A/C buttons. It changes modes (except AC does not work) but always directs air to the defrost position. Please Help! I cannot afford a shop at this point. :banghead: :banghead:

I don't know how the 1990 differs from my 87, but there should be a vacuum modulator on the back of the heater A/C control unit that is responsible for directing airflow. It can get corroded over time.