Re: 1996 Alfa 164 Super 24V - A/C Gas Type ?!
I think you've probaby got to the point where you need to take it back to the guy who re-gassed it and ask him to sort it out!
Something else you could try would be not to use the aircon in the morning. Wait until the hottest part of the day (when you say it is barely working at all) and then turn it on. If it initially gets cold (even in the higher ambient temperature), it might be that there is moisture in the system which is freezing in the expansion valve and blocking it temporarily. This is unusual but I have heard of it before!
The expansion valve is basically just a very small hole! (it's more complex than that on a car but I don't fully understand exactly how they work)! When you compress a gas and liquefy it, it gets hot because you are doing work on it (a but like a bike pump when you blow a bike tyre up - the end of the pump compresing the air gets warm). When you allow the liquefied gas to expand again, it needs to take heat from its surroundings to expand. It therefore cools the area immediately around it. If you have an air compressor nearby, you can see the same effect. The compressor cylinder will get hot because it's doing work on the air, but if you then get a blower nozzle or an air tool and start using it, you'll notice the end of the air nozzle getting very cold.
The aircon system works the same way. The compressor compreses the gas (which makes it hot). It travels along the pipe from the compressor (which is the one you can feel that's warm) until it gets to the condenser in front of the radiator. Here, the air passing through the vanes of the condenser encourages it to turn into a liquid. It then carries on until it gets to the expansion valve - which is just a small pinhole. As it passes through, it is no longer compressed but is allowed to expand - turning back into a gas again. This expansion causes it to take heat from its surroundings (which, by now, is the evaporator inside the car's heater box - just behind the pollen filter) and in doing so, the air pasing through the fins of the evaporator is cooled. After that, it then passes back to the compressor (along the return pipe which is the one you can feel to be cold) where the cycle begins again.
If it were my car, I think I'd do as Jason suggests and change both the dryer and the expansion valve AND make sure it has the corretc "PAG" oil AND make sure that the system is very well evacuated with a vacuum pump before refilling!