Your nose blockage with AC exposure is likely due to allergic or non-allergic rhinitis, where cold, dry air irritates the nasal lining and causes swelling. Frequent use of decongestant nasal sprays can also cause rebound blockage if used for many days. Try using a saline nasal spray regularly, keep the room air slightly humid, and avoid direct AC airflow on your face. If symptoms persist, a doctor may prescribe an anti-allergy tablet or a steroid nasal spray for longer control. Avoid using regular decongestant sprays for more than 3-5 days continuously.