do you hear the compressor clutch click when you switch to auto? check the sight glass next to the drier (under bonnet, right up by windscreen) do you see liquid flowing through this when the aircon is on?
When did the system last give you cold air?
When on econ mode do you get the full range of temps from what you call warm right up to hot when temp set to max?
This is the time of year loads of people start realising they should have used the aircon in the colder months from time to time to ensure the seals in the system do not harden. Come back with info.
Hmmm it almost sounds like one or more of the stepper motors may have failed which is not a pleasant job to do. I havrnt heard of a 24v model being affected by this though but the older 12v models were plagued with it. You usually get a clicking/grinding noise from the stepper gears before the teeth on the cog finally break but it may have been doing that before you got the car.
I suggest you post your peoblem in the technical section here http://www.digest.net/alfa/FAQ/164/ there are many 164 owners with alot more experience with this particular problem than me.
Note: The sight glass is situated next to the dryer unit (small cannister under windscreen inside engine bay) and is a very small glass window built into the pipe. If you do not even get remotely cold air when in Econ mode (yes this turns aircon off) then the flap inside cannot be redirecting air.
If you are not getting a click from the compressor clutch when engaging aircon then yes it may well be low pressure but check first to make sure the wire(s) going to the compressor have not broken or come loose.
If you would like a copy of the 164 Cardisc let me know, it is very good for fault finding and repair stuff. I also have the 2003 version of the Alfa parts CD.
As warm air is comming in with "Econ" mode I'll ignore the aircon side for now, and concentrate on the flap redirecting warm air. Presumably the stepper motors still operate in "Econ", to open flaps etc.?
Can you supply Cardisc manual. Please advise costs etc (can it be downloaded from anywhere?)
Do you know which flap I should be looking at? I have the parts CD which is good for getting exploded diagrams of units.