There are two possible causes for this phenomenon.
For one, your eyes may be sensitive to the cold wind hitting your cornea. When cold air, dirt, sand, or other foreign bodies enter your eyes, your eyes water to protect themselves from irritation.
For the other, you are likely to be suffering dry eye syndrome lately. If you have dry eyes, your eyes are more sensitive to the exposure of the air, light or whatever.
Generally speaking, it is normal that eyes will get watery when you are facing directly towards the fan which is running on. It is because that the wind blows straight into the eyes irritating the nerves of the lacrimal gland and making it begin to produce tears. However, if the condition is serious, then you may as well consider that might be some disease in the efflux system of tears. It may due to the blocked or too narrow lacrimal passage or acute or chronic dacryocystitis. If so, you had better go to the doctor's for an eye examination and related measures such as syringing of lacrimal passages and X-ray iodine oil radiography. And after that, certain medicines or operation treatment should be taken on according to correspondent pathogenesis. Pay attention that your eyes need adequate rest as well as good eye hygiene. Besides, add more vegetables and fruits to your daily diet. Do not drink too much and never smoke.
Maybe your eyes are so sensitive. Or your eyes have got the infection because of the coming invisible bacterium. You need to protect the eyes carefully. You could use the eye drops with anti-inflammation to make the eyes get moisture. You could also use the warm compress as the good home remedy to make your eyes feel comfortable.