Hi,
theoretically the air-con should be functional if it is agreed so in the purchase contract, and the developer is liable for that by contract law. However, the producer of the air co should also have a guarantee which would cover any defects others than the installation. Finally, if there was an installer (outsourcing), they are liable for the installation as well.
Our suggestion would be to request IN WRITING and THROUGH BUROFAX that the Developer either repairs the air co installation or at least that they give you the details of the installer and the producer's guarantee. If you do not do this, all your calls etc will simply be nearly useless.
Finally, in your case the typical defence from the developer, installer and producer would be saying that the defect has been caused by you, or by misuse, etc. Please try to involve someone skilled in the installation of such systems so that he can attest if necessary at court where the problem lies.