I have a vw bora 2002 model... the radiator fan for this car starts as soon as i start the car n stops when i shut the car.... can you tell me why is this happening

Your AC compressor is activated via Climatronic control. The system regulates inside temperature activating the compressor or opening the flap from the heater core. This will be automatic when you set the temp you desired inside the vehicle. Unless you see the words ECON on the right side of the LCD display, your AC compressor will be engaged and the rad fan will operate to prevent the engine from over heating. Press ECON until you see it displayed and it will disengage the compressor and use only the interior blower fan to regulate the inside temp by opening the outside air flap and not from the AC.