BMW mirrors snap into the motor that moves them up/down/right left. There is another electrical connection to the mirror itself that performs the defrost. Essentially, the mirror is coated with a resistor like material that heats up the surface when electricity is applied. You can safely remove the mirror itself by simply pulling it away (toward rear of car) and it will snap out of the motor/actuator. Yeah, its that easy.
If the mirror is just not defrosting ... simply replace mirror. If the motor is busted, it requires taking off the interior door panel to gain access to the bolts that hold the mirror assembly on. Ive done it on my old E46. Not fun, but not impossible.
Sounds like you have another problem if both motor and defrost are not working as they are separate systems.
Last edited by bluskye; 11-16-2011 at 06:57 PM.