Every air conditioner comes with manufacturer's warranty, that must be honored by the installer. Make sure your installer and contractors are qualified dealers for the brand you choose. If your air conditioner fails or was not installed properly your warranty will not be honored..
Extended warranties are available at additional cost. Make sure you get your warranty in writing when accepting a proposal. Read through your warranty certificate in your installation manual, to make sure you are familiar with all the terms and conditions.
Most installers only do warranty repairs on units they installed themselves. This is why it is important to deal with reputable contractors who will not shut down overnight, leaving you to deal with warranty issues. Remember that to carry warranties contractors have to be licensed and trained on the air conditioners they sell and install.. If the manufacture does not feel the contractor or technichian who does the install was qualifird you lose.
A good installation from a good company eliminates most repairs!