When considering an HVAC contractor, ask to see documentation that they carry general liability insurance to protect your property as well as workers compensation insurance on their employees. Lack of adequate insurance could be a major problem for you if someone is injured on your property. An air conditioning contractor should always have these types of insurance and this will save you from a claim against your homeowner’s policy in case of an accident.
Another source for finding a competent HVAC contractor is the local permits office for your municipality. The municipal inspectors know the HVAC contractors who do good work from the HVAC contractors who do poor work.
Once you identify and contact several HVAC contractors, set up an appointment with each of them to visit your home. You should not be charged for this initial appointment. During the meeting the contractor should inspect your existing air conditioner and collect a wide range of information about your home: how many windows and type, which directions they face, and R-value of the insulation. The contractor uses all of this information to calculate the heat load to verify that the existing equipment is correctly sized and proposed equipment is also correctly sized. You should receive a written estimate from each contractor. If one contractor submits a bid that is dramatically different from the other bids ask the contractor to explain the difference. Some HVAC contractors represent only one line equipment and using these contractors has advantages and disadvantages. On the plus side the contractor has probably gone through specialized training offered by the manufacturer. Should there be any problems with equipment performance you may have additional leverage because you may be able to involve the manufacturer. If you get estimates from contractors that sell other brands, make sure they are recommending equivalent equipment.