300zx heater/air conditioning function intermittently

[robtab]

They actually function all the time, but sometimes I can hear the blower blasting a full stream of air, but it's not getting out into the car... it's like there's a door that's stuck shut which should have opened... in the summer, this results in a mist coming out at time... dealer has no clue... it won't seem to misbehave when he has the car....anyone know of this kind of problem? is there a door or something that opens and closes?00

[180fan]

follow the ducts behind the dash. There should be a flap that guides air to different chambers.

[NISTECH]

When it does this make sure all you dash vents are in the open position. If thats ok start feeling around to see if it is blowing out the wrong vent. Check at the defrost grille on the dash, and near your right foot on the floor. It would be extreamly difficult for the mode door to completely block off air flow from ALL vents.