Hi, i had same problem with my Laguna , the heater unit is located passenger side under dash just above foot level, you dont have to remove dash to get to it , there is a soft felt cover. First thing to do is check the connector blocks under there as people can accidently catch them with their feet and the connector or a wire going to it becomes loose, try some jiggling and maybe clean the block with meths or proper switch cleaner,(dry off all flamable substances with a hairdryer before reconnecting) I had been driving around freezing for 3 weeks last winter before finding this easy and quick solution, if this doesn't do it let me know as I have the manual , cheers and good luck
Aaron
Laguna Dci owner, September 2009