ok, so ive had my z for a couple of months now. it is an 04 model that i believe was manufactured in 03. the first month or so i noticed no problems with the ac/heater. i usually had the temp set to around 67-70 and owuld just leave it there and have the fan set at about 1/3. then all of a sudden one day on the way to work i realized i was hot and had to turn the temp all the way down to 64 to even get soemthing other than HOT air to blow. so from only 60-64 did it blow cool air, not even cold air. thi doesnt happen allthe time, only sometimes. and to be honest it seems to only happens if its kinda cold outside. makes me wonder if theres not some kind of auto temp, i know the temp control **** has one but its not set to auto, internally that knows its cold outside and adjusts the temp settings accordingly. is this jsut a stupid idea or what?
basicaly my a/c is acting wierd and sometimes blows almost all warm/hot air and braely any cool and sometiems actsnormal. btw ive searched this topic and not really found any help. just to give an example, the last few mornings on the way to work its been like 30 degrees outside and i have my a/c set to 64 so i dont get hot.

 

Sounds like the computer circuit that contols the AC has gone bad on you. It's located just under the radio and in front of the shifter - a big white plastic box with three connectors plugged into it. It's high lighted in yellow in the picture below. Dis-reguard the termnal 20 markings - that's for the speed pulse.

 

You Are Exactly Right It Is Controlled By What The Outside Temp Reading Is.i Know Because I Had The Exact Same Problem And I Thought There Was Something Wrong And Even Called The Dealership To Set Appointment,thats When The Service Guy Explained It To Me And Said He Has Been Getting Calls About That.i Even Searched On Here And G35 And Seen Where Other People Found Out The Same Thing .any More Questions Please Let Me Know