It probably needs a re-gas. Open the bonnet and start the engine. Locate the larger of the two air conditioning pipes. This will be the low pressure return to the compressor. Switch on the A/C and touch the low pressure pipe with your hand. After a couple of seconds the pipe will become noticeably cold, and even sweating with condensation. If it doesn't your system is low on gas.

Smaller cars with smaller engines tend not to have powerful aircon. Remember, the power has to come from the engine. My Saab's aircon was working hard and probably consuming 10-12hp in doing so. Now that doesn't make a big dent in the 260 available from the engine, but if that aircon was in my wife's C1 with it's 69hp 1 litre motor, then the loss of 10hp would be keenly felt.

It's quite noticeable on warm days that the aircon in the C1 is not particularly effective - good enough to "take the edge off".

Same was true of my son's Polo 1.2.

That's why we were out in the Saab yesterday

I doubt there's anything wrong. It shouldn't have lost any performance at 2yrs old. It was probably giving it everything it had! But if you can get it checked for free, then why not (just watch those warranty conditions).

I think no, mainly manufacturers keepn an eye on every subject and every detail of car. So problem may occur not because of manufacturers