Hello Sudden increase or decrease in temperature ,humidity , dust , mite pollen ,fumes are certain predisposing factors responsible for allergy in few persons , your son may have this problems . One option is remain away form direct contact with air conditioner air . But outside , he can t remain away. This is usually due to allergens in air . When such patient visit I prescribe them to take montelukast+fexofenadine ,combination ( tablet ) once or twice in day depending on severity of symptoms ( however, the normal dose is once in the night ).But this is a prescription medicine ,so take a prescription from your doctor. Hot coffee and steam inhalation provide instant relief. Avoidance also help. Get in blood examination for allergy test. Hope this will be useful for you son.