What causes the fan turns on every 30 seconds when car is off, and drains the battery?

What is your question?

Changed the temp control sensor, which the obd code reader said was wrong. But it still turns on the fan, on the passenger side of engine. Every 30 seconds, even if it's been parked for hours. And the air conditioning doesn't blow cold when this happens.

What makes this problem better or worse?

Doesn't matter, makes the air conditioning not work.

How long has your 2003 Volkswagen Passat had this problem?

A couple days.