Its been a while since anyone posted here, but I ran into the whole no heat issue recently and as winter is here I figure this info could be useful.
After verifying I was getting coolant flow through the heater core it became pretty obvious I had a problem with the mixer door not actuating back to the hot side. I removed the glove box and the metal plate behind it. Just left of this opening is the servo and linkage for the mixer door. As I have no intention of using cold air through winter, I simply disconnected the linkage from the servo and pulled it to the passenger side of the vehicle. This put the mixer door into the heater side and I have heat again. Obviously this is just a temporary fix, but it will get you defrost again...
Oh,, this was a 1990 pathfinder 4x4
