Posted this on "that fan in the roof" but thought it might get more "viewers" here.

 

Here's a few things you might not know:

If you set the air con to Econ (Economy) it switches off the compressor and as has been said just uses the air from outside and heats it if needed. As the compressor is not being driven you get better fuel economy. The only time the compressor is required is when cooling the air to below the outside air temp.

If you floor the throttle the ECU turns off the compressor for a while to give you more power!

If the upper cabin is cold and the footwell is warm, the upper fans will come on fast and hot to quickly heat the upper area to the same overall temp. This is why sometimes the fans blast out fast and sometimes they don't.

In addition to the upper cabin, lower cabin and outside ambient temp sensors there is also a sun-load sensor to compensate for the heating effect of the sun! (don't ask me where this is, i've always wondered)

The system operates differently according to all these different sensors so it basicaly does what it wants - AUTO.

 

There is a diagnostic mode you can use to test out the fans etc:

 

General Info: http://www.300zx.co.uk/cgi-bin/ma nual.cgi?list=ha&dir=&config=&refresh=&direction=forward&scale=0&cycle=off&slide=95&design=default&total=168

 

Console Switch Functions: http://www.300zx.co.uk/cgi-bin/ma nual.cgi?list=ha&dir=&config=&refresh=&direction=forward&scale=0&cycle=off&slide=96&design=default&total=168

 

Trouble Diagnosis: http://www.300zx.co.uk/cgi-bin/m anual.cgi?list=ha&dir=&config=&refresh=&direction=forward&scale=0&cycle=off&slide=118&design=default&total=168

 

Hope this helps to explain why it seems to have a mind of its own - literaly.

It's a very complex system.

 

The sunlight sensor is to the the left of the left window demister (as you look at it while sitting in the car) No need to wonder anymore

 

Rob.

You learn something new every day as they say. I will sleep better at night now I know that useless bit of Z info