Hello, This is my first post. I am not trying to slam anyone just a little FYI. in response to this reply "Check the cable that goes to the fresh air vent which is behind the blower motor housing. If your vent is stuck open and not being closed by the cable, then you will be trying to heat fresh COLD air all the time. Yes eventually the heater will warm the air, but not HEAT it. " With the fresh air door in the closed position you will probably see condensation (fogging) begin to appearon your windows. I do not recommend driving in this mode. Recirculation mode is truely designed for 2 reasons 1)Max Air, is a recirculation mode, When the a/c is running. The evaporator acts as a dehumidifer, preventing fogging. 2) Air quality. When waiting at a light behind a desiel powerd vehicle, sorry they stink. By the way in today's cars the a/c runs when you are in a Defrost mode and the fresh air door will open automatically. Unfortunately I have yet to see a Z Car HVAC Unit yet as I am looking for a 240z myself. Thanks for Forum, Gene