Heater resistor
A common problem on many nissans is the heater fan working at the same speed for all switch settings, or similar.
The cause is a burnt out resistor card, which is located in the ducting behind the glovebox.
On the K11 the card can be accessed from below, without removing the glovebox.
The tracks eventually burn out when using the lower speed settings, which heat up the resistors, and also reduce the air flow which would otherwise cool them.
The card is commonly about the size of a credit card and it is posted into the duct through a slot. It has a plug connected to it with several cables, and pretty easy to spot.
Some nissans of similar year use the same card, so potentially there are a wider source of used cards.
Some people have successfully soldered the cards.
Some people solder high current resistors (components) between the burnt tracks.
Or you can buy new & replace.
See pictures here http://www.micra.com.au/community/message.php?messageid=50536