I had the same problem in my Almera. Turned out to be the heater resistor. This is attached to the blower motor which is in turn located behind the glovebox. Take out the glovebox and look under the dash where you will find the blower motor. Undo the multi plug and remove the two screws then withdraw the resistor.The resistor is slightly bigger than a credit card. I purchased mine form Nissan as i couldnt be bothered looking around the net etc. it was very easy to replace and works a treat.
LG
November 2005
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